Fluid and electrolytes

assessment and diagnostic findings

Assessment and Diagnostic Findings It is important that you assess the patient who might be at risk for fluid volume deficit as well as the patient who has already been diagnosed with the problem. Box 29-3 provides a list of signs and symptoms that may be indicative of fluid volume deficit. Diagnostic test results supporting fluid volume deficit may include the following: • Urine specific gravity is high or concentrated. • Hemoglobin and hematocrit, due to the increased concentration, may appear to be elevated or, in the case of hemorrhage, may actually be decreased. Note: It may take a while for the test values to drop in response to hemorrhage. • Blood urea nitrogen (BUN) may appear to be elevated due to the increased concentration. • Electrolytes may be within normal ranges if losses have been equal. If electrolyte losses are less than water losses, then the electrolyte laboratory values will appear elevated. This is due to the decreased ratio of water to solutes. Knowledge Connection List at least six signs and symptoms of fluid volume depletion. Explain how volume depletion affects urine specific gravity and hemoglobin results. Box 29-3 Signs and Symptoms of Fluid Volume Deficit Be alert for signs and symptoms that may indicate the presence of or risk for developing fluid volume deficit. Be especially vigilant when monitoring infants, children, and older adults, who are at increased risk for fluid imbalances. • Patient reports of little or no fluid intake or urine output • Patient reports of significant number of occurrences of vomiting or diarrhea • Flushed, pale, hot, dry skin with nonelastic turgor (nonelastic turgor is a very late sign) • Complaints of thirst or nausea • Dry, cracked tongue and lips • Elevated heart rate • Weak pulse • Fever • Low blood pressure • In young children, soft feel of eye globe when gently palpated through the eyelid or eye globe sunken into the face • In newborns, sunken or depressed fontanels • Decreased level of consciousness (severe fluid volume deficit) • Confusion (severe fluid volume deficit) Treatment and Nursing Care Cautious fluid and electrolyte replacement is a priority. Infusion of IV fluids with appropriate electrolytes is the primary treatment. However, rapid infusion of IV fluids can result in electrolyte imbalance and place stress on the heart and kidneys. Oral fluids, including electrolyte fluids, also may be ordered if the patient is able to keep them down without vomiting or diarrhea. However, a patient with extreme fluid volume deficit may not be able to absorb fluid through the GI tract. In this case, only IV fluids will be administered. Monitor electrolyte levels closely. If the GI tract is the source of loss, antiemetic medications may be ordered for nausea or vomiting, or antidiarrheal medication for loose stools. Once the patient is able to tolerate oral fluids, a clear liquid diet advanced as tolerated is generally ordered. Monitor vital signs for low blood pressure, elevated pulse rate, and elevated temperature. Measure and monitor intake and output for balance. Normally, the output total should be equal to or within 300 to 500 mL of the total intake. So in a patient with fluid volume deficit, the urinary output initially will be absent or less than the intake but should gradually increase as the patient becomes more hydrated. Persistent urinary output below 30 mL/hr may be indicative of renal failure if the deficit was severe and prolonged. Make certain each patient voids at least every 8 hours, and notify the physician if a patient fails to void. Continue to assess for further losses by observing for profuse diaphoresis, measuring volume of emesis and liquid stools. Safety: Even though a patient who has fluid volume deficit needs fluids, rapid infusion of IV fluids may cause fluid volume excess, or overload. Monitor all patients who receive IV fluids for signs and symptoms of fluid volume excess, including auscultation of breath sounds, noting adventitious sounds, to ensure that the patient is not developing signs of fluid overload. Also monitor for rapid increase of blood pressure, increased pulse volume, and tachypnea. Observe for dyspnea and cough. Assess the patient's oral mucous membranes for dryness and provide mouth care as needed. If oral fluids are not allowed, the physician may order ice chips as long as the patient is not vomiting. Knowledge Connection

baroreceptors

Baroreceptors A baroreceptor is a sensory nerve ending that detects, or is stimulated by, changes in pressure due to the blood volume. Another term for baroreceptor is pressoreceptor. These receptors are located in the atrial walls of the heart and in the inferior and superior venae cavae, as well as in the aorta and the carotid sinus located at the base of the internal carotid artery. When pressure changes are detected, the baroreceptors send a message to the central nervous system to either increase or decrease arterial diameter and increase or decrease heart rate. Knowledge Connection Which electrolyte is key to fluid moving in and out of cells and capillaries? What are the effects of ADH on the body's fluid level? What effect does aldosterone have on the body's fluid level? How does ANF affect production of urine? What will this do to the body's fluid level? How much daily water intake does the U.S. Department of Agriculture recommend for women? For men? Figure 29-3 Renin-angiotensin-aldosterone system. Fluid Volume Disturbances Determining the type of fluid volume disturbance is not a simple measurement of just the fluid lost or gained. It must be determined if the patient has lost both water and electrolytes; has lost more fluid than electrolytes; or has experienced an increase in both fluids and electrolytes or in body fluid only. Fluid Volume Deficit A true fluid volume deficit, also known as hypovolemia, only results when there is an equal loss of both fluid and the electrolytes contained in that fluid. The water-to-solute ratio in the body must remain balanced even though there is a loss, as would be the case when an individual hemorrhages. With blood loss, there is equal loss of water as well as solid components of the blood, such as electrolytes, protein, red blood cells, white blood cells, and thrombocytes. If there is loss of fluid only, resulting in an increase of electrolyte concentrations in the remaining body fluid, it is called dehydration. It is pertinent that you are able to detect the differences because they require different treatments. We will cover dehydration later with the electrolyte disturbances. Table 29-1 Estimates of Adult Fluid Loss and Gain per 24 Hours Loss or Gain Fluid Source Volume Loss Urine 1200-2100 mL Diuretics can cause loss up to: 6000 mL Loss Insensible respirations 200-300 mL Loss Gastrointestinal tract 100-200 mL Vomiting can cause loss up to: 6000 mL Loss Insensible perspiration 400-600 mL If environmental temperatures are high enough, can cause loss up to: 1000 mL/hr Gain Water production through metabolism of ingested food 100-300 mL Gain Oral liquids 1000-2000 mL Gain Water in food 800-900 mL Causes of fluid volume deficit can be related to prolonged insufficient fluid intake or loss of fluid. Some patients experience a lack of thirst, called adipsia. This is a common problem for elderly individuals who lose their sense of thirst over time. This can also occur for patients with brain injuries. Safety: Young children, who are dependent on others to provide them with fluids, can develop a fluid volume deficit if they go without fluids for a prolonged time. Extreme nausea, even though there is no vomiting, may prevent someone from drinking fluids for several days. Another source of fluid deficit might be abnormal fluid losses. Losses can be due to bleeding, prolonged tachypnea, excessive sweating, fever, diarrhea, vomiting, or excessive urination due to diuresis. Severe depletion of fluid volume can also occur in hot climates or with extreme amounts of exertion or exercise. It is important to understand that fluid volume deficit can occur in varying degrees of seriousness based on the degree of loss, ranging from mild to life threatening. Knowledge Connection What is the difference between fluid volume depletion and dehydration? What causes fluid volume depletion? People and Places Connection: Fluid Intake in Elders Seniors, whether they live independently or with caregivers at home or live in a long-term care facility, are at high risk for dehydration. Many seniors experience a declining sense of thirst due to changes in the brain. When this occurs, either the senior or the caregiver will need to ensure that the senior is drinking water, even when he or she does not feel thirsty. The recommended amount of fluid intake per day is about 1800 mL, or 2 quarts. Alcohol and dietary supplements are less hydrating than water. Some liquids such as coffee and tea can also have a diuretic effect. Elderly patients with cardiac or kidney disease, however, may be placed on a fluid restriction. These seniors will need to monitor how much fluid their physician or nurse practitioner has prescribed for them to take daily, monitor their daily weight, and watch for increased or decreased amounts of urine production.

calcium

Calcium (Ca2+) is the most common mineral in our bodies; 99% of it is combined with phosphorus and located in the bones and teeth, with the remaining 1% located outside the skeletal system in the blood. This 1%, known as the total serum calcium level, easily and rapidly exchanges back and forth between the blood and bone. The serum calcium level is controlled by calcitonin, excreted by the thyroid gland, and parathyroid hormone (PTH), excreted by the parathyroid glands. When the serum calcium level becomes low, PTH is excreted, which causes release of calcium from the skeletal system into the blood to maintain adequate serum level. When the serum level of calcium elevates above normal, the thyroid excretes calcitonin, which increases resorption of calcium from the blood into bone, lowering the serum level. Approximately half of the total serum calcium is ionized, meaning that it is physiologically active for use in various body functions. Ionized calcium helps control the permeability of cellular membranes and assists with blood coagulation. Ionized calcium stimulates transmission of electrical impulses along nerve pathways, including the electrical conduction pathways of the heart that control contraction and relaxation of the heart. This control of electrical impulse conduction regulates contraction and relaxation of muscles throughout the body as well. Initiation of various essential chemical processes depends on ionized calcium to activate the appropriate enzymes. The remaining half of the serum ionized calcium is bound with protein, mostly with albumin. Use care to differentiate between the total serum calcium and the ionized calcium values when you review laboratory results in the medical record. Normal ranges for total serum calcium should be twice as high as those for ionized calcium (see Table 29-2). It is estimated that we need 1200 mg of calcium each day. Children require higher levels because of the rapid metabolism of calcium by their growing bones. Because vitamin D is required for absorption of calcium from the GI tract, individuals who consume enough calcium but are not getting adequate vitamin D may not be absorbing their dietary calcium. Individuals who do not normally expose their skin to the sun are at high risk for vitamin D deficiency. Less calcium is absorbed from the GI tract and an increased level of calcium is excreted by the kidneys as we continue to age. Calcium Imbalances: Deficiency and Excess Hypocalcemia is defined as having lower-than-normal serum calcium. It is common with diseases that cause poor digestive absorption, such as anorexia or inflammatory bowel disease. Because calcium is necessary for adequate blood clotting and control of excitable tissues, hypocalcemia may increase bleeding and result in cardiac arrhythmias. Chronic low calcium levels can cause loss of bone and high blood pressure. You may recall that weight-bearing exercise increases bone strength by stimulating serum calcium to be deposited into the skeletal system. The opposite occurs when a patient remains on bedrest for extended periods of time. The lack of weight-bearing exercise increases the rate of resorption, removing more calcium from the bones and absorbing it back into the bloodstream. This can result in an excessive serum calcium level known as hypercalcemia, which can affect the electrical rhythm of the heart. Chronic high levels of calcium can contribute to kidney stones, which often are undetected until the patient complains of severe flank pain (see Table 29-3). A disease known as osteoporosis causes a higher level of calcium resorption than the level being deposited in the bones. Resorption is the process of removing calcium from the bones and absorbing it back into the bloodstream. The higher level of resorption leaves the bone structure weakened, with tiny holes or gaps within the bone, giving it a honeycomb appearance. Because of their weakened structure, the affected bones are easily fractured, sometimes without a stimulus such as a fall. For example, a patient may present for treatment reporting that he or she fell. Upon examination, a femur fracture is identified. Your first thought may be that the fall caused the fracture, which is normally the case. However, a patient with severe osteoporosis may experience a fracture without trauma, which then causes the individual to fall because the broken bone is no longer able to bear the person's weight. This is known as a pathological fracture. It is important to remember that even though a patient has a healthy serum calcium level, he or she may have a severe deficit of total body calcium. Treatment and Nursing Care Hypocalcemia is treated with oral tablets or IV calcium along with vitamin D to increase gastrointestinal absorption of calcium. Certain forms of IV calcium are extremely irritating to veins and can cause serious problems if allowed to extravasate into the subcutaneous tissues. Safety: Intravenous infusion of calcium also can cause bradycardia and death if administered too rapidly, thus making it a necessity to use a volumetric infusion pump and assess the IV site and rate of infusion every 30 to 60 minutes. You should keep the patient receiving IV calcium on bedrest during infusion and monitor the blood pressure for hypotension, a side effect of IV calcium. You will need to monitor the patient with hypocalcemia for muscle twitching and tetany as well as for cardiac irregularity. You will need to assess for spasms of the facial muscles and the arms and legs, and tingling around the mouth or tips of the fingers. The patient may become disoriented and confused. Some have even been known to have hallucinations. It is common to find the patient with hypocalcemia experiencing depression. There may also be electrocardiogram changes: the lengthening of the interval between the onset of the QRS complex and the beginning of the T wave. Patients suffering from hypocalcemia may also present with Trousseau's sign (Fig. 29-4) and Chvostek's sign (Fig. 29-5). If hypocalcemia is due to a problem with the kidneys or the parathyroid gland, then the treatment is focused on those organs. Extreme hypocalcemia requires immediate treatment to stave off death and may need IV administration of calcium to raise the serum level and of bisphosphonates to prevent further bone breakdown. Figure 29-4 To check for Trousseau's sign, inflate a sphygmomanometer above systolic pressure. Flexion of the wrist and hand constitutes a positive sign. (From Wilkinson JM, Treas LS. Fundamentals of Nursing: Theory, Concepts & Applications. Vol. 2, 2nd ed. Philadelphia: FA Davis; 2011.) Figure 29-5 To check for Chvostek's sign, tap the face in front of the ear and below the zygomatic bone. Facial twitching constitutes a positive sign. (From Wilkinson JM, Treas LS. Fundamentals of Nursing: Theory, Concepts & Applications. Vol. 2, 2nd ed. Philadelphia: FA Davis; 2011.) Treatment of severe hypercalcemia is focused on reducing the excessive calcium in the blood because of the 50% mortality rate if not resolved promptly. Encourage fluids and monitor IV infusions, if ordered, to help dilute the blood level of calcium. If IV normal saline solution is administered, it may be in conjunction with furosemide, a diuretic that increases urinary excretion of sodium and calcium. Calcitonin also may be ordered to increase calcium exchange from blood to bone, thus lowering the blood level. If the patient takes digitalis, a drug that increases the strength of cardiac contractions and slows the pulse, it will be important for you to assess for signs of digitalis toxicity as hypercalcemia potentiates (or magnifies) the digitalis effects. Monitor the patient for bradycardia, digestive complaints, and visual disturbances.

chloride

Chloride Chloride (Cl-) accounts for approximately two-thirds of the body's anions and is commonly bound with sodium or potassium ions. It shares a direct relationship with sodium and an inverse relationship with bicarbonate. The majority of chloride is bound to sodium in dietary sources as well as in the body, and usually is consumed in the form of table salt. Much of the remaining chloride is bound to potassium in the form of potassium chloride. Chloride is found in interstitial fluid, lymph fluid, sweat, and gastric and pancreatic digestive juices, with lesser amounts in the blood. Chloride combines with hydrogen to form hydrochloric acid in the gastric juices of the stomach, which is used to break down foods. Other functions of chloride include regulating the osmolality of the ECF and assisting in maintaining the body's acid-base balance. The daily dietary requirement of chloride for adults is 2300 mg/day. The primary route of excretion is through the kidneys, with a small amount lost in the feces (see Table 29-2). Chloride Imbalance: Deficiency and Excess Chloride is nearly always chemically bonded to another electrolyte in the body. As a result, chloride imbalances are most commonly seen in combination with other electrolyte imbalances, such as hyponatremia or hypernatremia, with similar signs and symptoms, and is caused by the same factors. A below-normal serum level of chloride is known as hypochloremia. When the chloride level continues to drop, the kidneys attempt to balance the loss by conserving sodium and bicarbonate, which may result in an increased bicarbonate level in the ECF. This raises the pH and leads to metabolic alkalosis, which you will read more about later in this chapter. Hyperchloremia describes a serum chloride level above normal. Its occurrence is rare except when it accompanies metabolic acidosis. Because it is so directly related to the sodium level, it may be associated with hypernatremia as well as with bicarbonate loss due to the inverse relationship. Its association with metabolic acidosis is usually due to renal or gastric loss of bicarbonate, which increases reabsorption of chloride that forms acidifying salts. As the level of acidified salts increases and bicarbonate continues to decrease, metabolic acidosis results (see Table 29-3). Treatment and Nursing Care Depending on the severity of hypochloremia, treatment to restore the chloride level to normal may range from an increase in dietary sodium chloride to infusion of IV fluids, such as 0.9% or 0.45% sodium chloride. (See Table 29-2 for a list of foods high in sodium chloride.) If the patient has been receiving a diuretic, the physician will determine whether to change it to a different diuretic or to discontinue it. It will be important that you monitor intake and output. If the patient routinely drinks water without electrolytes or bottled water, the physician may restrict the patient from drinking it. Fluid loss through vomiting or diarrhea must also be measured to monitor appropriate replacement. High and low levels of chloride can change the acid-base balance of the body and cause serious neurological and respiratory changes, so these conditions must be managed carefully. When hyperchloremia is associated with metabolic acidosis, the primary treatment is to correct the acidosis by administering diuretics to lower blood levels of chloride. It may be necessary to administer IV sodium bicarbonate to help raise the serum (blood) level of bicarbonate and decrease the acidity. For mild hyperchloremia, lactated Ringer's solution is administered because it converts to bicarbonate in the liver. This serves to increase the base bicarbonate level, which helps to correct acidosis. It is important to monitor the patient's intake and output and laboratory results.

electrolytes

Electrolytes Electrolytes are chemical substances that, when dissolved in water, release either their positive or their negative electrically charged particles, called ions, which are capable of conducting electrical current. An anion is a negatively charged ion such as chloride (Cl-). A cation is a positively charged ion such as sodium (Na+) or potassium (K+). Electrolytes play various roles, including helping to transmit electrical impulses through nerve and muscle fibers and assisting to maintain balance between the ICF and ECF compartments. Table 29-2 presents the normal ranges, functions, and sources of the various electrolytes. Sodium Sodium (Na+) is the most abundant cation in the ECF compartments, including the blood, with serum levels ranging from 135 to 145 mEq/L. It is also the primary electrolyte involved in determining ECF volumes and controlling the osmolality of the fluids, which in turn controls fluid distribution throughout the body. Sodium stimulates conduction of electrical impulses, thereby helping to maintain the neuromuscular irritability that is required for skeletal and heart muscles to function. Certain medications work to increase either fluid excretion or fluid retention by causing sodium to move across cellular membranes and capillary walls (see Table 29-2). Table 29-2 Electrolyte Ranges, Functions, Regulation, and Nutritional Sources Electrolyte, Cation, or Action Location in Body Normal Blood Range Regulation of Blood Level Functions Sources for Intake Sodium (Na+) Cation Extracellular fluid (ECF)* 135-145 mEq/L Changes in direct proportion to Cl- Regulated by antidiuretic hormone (ADH) and aldosterone Reabsorbed and excreted by kidneys Requires active transport to cross cell membranes Controls fluid osmolality and volume of blood Stimulates conduction of electrical impulses along nerves Works with calcium to regulate muscle contraction Salt: Most individuals obtain 90%-94% from packaged, processed foods, including bacon, ham, canned vegetables, soy sauce, steak sauces, other sauces, salad dressings, processed cheeses, sandwich meats, salty snacks such as chips, jerky, pretzels, canned soups, broths Adding table salt to prepared foods Chloride (Cl-) Anion ECF* (mostly interstitial compartment) Part of HCl in gastric juices 97-107 mEq/L Changes in direct proportion to sodium Has inverse relationship with bicarbonate Reabsorbed and excreted by kidneys Regulated by ADH and aldosterone Low level of potassium will lower Cl- level Assists sodium in regulating fluid osmolality and volume Important for acid-base balance Production of gastric HCl High-sodium-content foods listed above Lettuce, tomatoes, celery, olives, seaweed Potassium (K+) Cation 98% intracellular fluid (ICF)* 2% ECF 3.5-5.3 mEq/L Diuretics cause loss Gastrointestinal (GI) disturbances cause loss Reabsorbed and excreted by kidneys Regulated by aldosterone 98% in ICF helps regulate fluid balance 2% in ECF is important for neuromuscular functions, especially for the heart's contractility and rhythm Dried fruits, tomatoes, potatoes, spinach and other leafy greens, oranges, bananas, cantaloupe, red meat, chicken, fish, nuts, soy products Magnesium (Mg2+) Cation 99% bones and ICF (second most abundant ICF cation) 1% ECF 1.6 -2.6 mEq/L Amount present in diet Malabsorptive conditions Small bowel resection Excreted by kidneys Low albumin level decreases Mg2+ Assists neuromuscular function; dilation of arteries and arterioles; enzyme function; carbohydrate and protein metabolism Leafy green vegetables, whole grains, beans, fish (halibut), almonds, soybeans Bicarbonate (HCO3-) Anion ICF and ECF Kidneys excrete and reabsorb it 22-26 mEq/L Has inverse relationship with Cl- Reabsorbed and excreted by kidneys Diuretics cause loss Renal disease causes loss GI disturbances cause loss Primary buffer for acid-base balance Primary dietary source: baking soda Produced by body Calcium (Ca2+) Cation 99% bones and teeth (ICF) 1% ECF Half of this 1% is ionized Ca2+ and half is protein bound Total Ca2+: 8.2-10.2 mg/dL Ionized Ca2+: 4.6-5.2 mg/dL Combines with phosphorus in bones and teeth Inversely proportional with phosphorus Vitamin D Calcitonin lowers blood level Parathyroid hormone raises blood level Strengthen skeletal bones and teeth Ionized Ca2+: stimulates conduction of electrical impulses via nerves, which controls muscle contraction and relaxation, includes heart muscle Initiates enzyme action Cellular membrane permeability Dairy products, green vegetables, shellfish, salmon, dried beans Phosphorus (PO43-) Anion Located in every cell of the body 2.5-4.5 mg/dL May be higher in children Combines with phosphorus in bones and teeth Inversely proportional to calcium Parathyroid hormone Vital for all tissues; muscle and red blood cell functions; metabolism of fat, protein, carbohydrates; manufacturing ATP energy source Meats, fish, egg yolks, dairy products, nuts, beans, legumes, whole grains, soft drinks *The most abundant cation and anion found in the intracellular and extracellular compartments. In the blood, sodium in measured in milliequivalents (mEq); in food, it is measured in milligrams (mg). Safety: The American Heart Association recommends that healthy adults consume no more than 2300 mg/day. This is about 1 teaspoon of table salt, or sodium chloride. Safety: For individuals who fall within the following population groups, it is recommended that they consume no more than 1500 mg/day: • Individuals with hypertension • Individuals who are 40 years of age or older • African Americans Sodium Imbalances: Deficiency and Excess Hyponatremia occurs when the serum level of sodium falls below normal. This can be caused by decreased sodium intake, a loss of body fluids containing sodium, or an excessive intake of water that does not contain sodium, which is known to result in dilutional hyponatremia. As sodium levels in the extracellular compartments decrease to a lower level than that which is inside the cell, an imbalance develops. In an attempt to equalize the sodium concentration on both sides of the semipermeable membrane, water is pulled into the cells to dilute the sodium concentration to the same concentration as that on the outside of the cells. This results in swelling of the cells and causes potassium to be shifted out of the cells. Safety: Dilutional hyponatremia can be inadvertently caused by medical health-care providers by administration of multiple tap-water enemas, repeated irrigation of nasogastric tubes with tap or distilled water, and infusion of excessive sodium-free IV fluids. A patient can also develop dilutional hyponatremia by compulsive drinking of abnormally high volumes of tap water, usually attributed to mental illness. Hypernatremia is the condition of a higher-than-normal concentration of sodium in the blood, which can lead to death if not corrected. Most sodium excesses are caused by eating too much sodium chloride, or salt. Most individuals think of sodium intake as "only that salt they have sprinkled on their food." However, that is not the case because a significant amount of sodium can be found in canned and processed foods. Even some prescription and over-the-counter medications contain sodium in the form of sodium bicarbonate. Sometimes hypernatremia is caused by severe dehydration that decreases the solvent (water) level without decreasing the sodium level. Thus, the same number of sodium ions in a smaller volume of water simply increases the concentration of the sodium, disrupting the normal fluid and electrolyte balance. As discussed earlier in the chapter, the various imbalances impair the normal functions of the specific electrolyte that is out of balance. Hypernatremia causes fluid to shift from the cells to the interstitial spaces, which causes the cells to dehydrate. The dehydrated cells then are unable to function optimally, ultimately affecting the function of every body system. Signs and symptoms of sodium imbalances are listed in Table 29-3. Table 29-3 Electrolyte Imbalances Electrolyte Imbalance and Name Signs and Symptoms Causative Factors Sodium Deficit: hyponatremia Anorexia, nausea, vomiting, headache, lethargy, muscle weakness or twitching, nonelastic skin turgor, tremors, seizures, swelling of optic nerve Gastrointestinal (GI) suctioning, vomiting, diarrhea, ↑ blood sugar, congestive heart failure, renal disease, adrenal insufficiency, oxytocin, excessive infusion of D5W IV fluid, disease known as SIADH (syndrome of inappropriate antidiuretic hormone), administration of more than one tap-water enema, excessive diaphoresis Excess: hypernatremia Thirst, ↑ T, sticky mucous membranes, dry mouth, flushed skin, lethargy, restlessness, oliguria, ↑ irritability, hallucinations, seizures; pulmonary edema Diabetes insipidus; heat stroke; watery diarrhea; ingestion of excessive corticosteroids, sodium chloride, or bicarbonate Chloride Deficit: hypochloremia Signs of hypokalemia and metabolic alkalosis: ↑ muscle excitability, tetany, ↓ R, shallow R, agitation, irritability, seizures, coma ↓ intake of Cl- or Na+ such as sodium-restricted diet; potassium deficiency, excessive diaphoresis, diarrhea, vomiting, diuretics, gastric suctioning, congestive heart failure, IV fluids without Cl-, Addison's disease, metabolic alkalosis Excess: hyperchloremia Signs of metabolic acidosis, hyperkalemia, and hypernatremia: ↑ R rate and depth, dyspnea, ↑ P, ↓ cardiac output, arrhythmias, weakness, severe edema, ↓ LOC and coma ↑ Na+ serum level, respiratory alkalosis, hyperparathyroidism, severe diarrhea, sodium retention caused by head trauma and ↑ intracranial pressure, renal failure, salicylate overdose, corticosteroid use, diuretic use, dehydration, metabolic acidosis, administration of Kayexalate Potassium Deficit: hypokalemia Weak, rapid, or irregular P, ↓ BP, anorexia, nausea, vomiting, ↓ deep tendon reflexes, fatigue, muscular weakness and cramps, numbness, abdominal distention, ↓ peristalsis, ileus; may complain of seeing yellow haloes around objects if hypokalemia is caused by digoxin toxicity Diarrhea; gastric suctioning; vomiting; bulimia; starvation; diuresis due to osmotic diuretics; digoxin toxicity; administration of carbenicillin, corticosteroids, and amphotericin B Excess: hyperkalemia Bradycardia and other arrhythmias, nausea, intestinal cramping, diarrhea, anxiety, muscle weakness, numbness or prickly sensations, flaccid paralysis Renal failure, ketoacidosis, large burns, excessive use of K+-sparing diuretics, too-rapid IV administration of K+, severe dehydration Safety: Both severe deficit or excess can result in life-threatening arrhythmias. Magnesium Deficit: hypomagnesemia Vomiting, anorexia, insomnia, arrhythmias, mood swings and hyperirritability, dizziness, ↑ neuromuscular irritability, muscle weakness and tremors, positive Chvostek's and Trousseau's signs Starvation, malabsorption disorders, ketoacidosis, alcoholism and alcohol withdrawal, administration of gentamicin, hyperparathyroidism, vomiting Excess: hypermagnesemia ↓ BP, ↑ P, ↓ R, hypoactive reflexes, muscle weakness and paralysis, drowsiness, lethargy, flushing, diaphoresis, cardiac arrest, death Late renal failure, adrenal insufficiency, excessive administration of IV Mg2+ or oral antacids Calcium Deficit: hypocalcemia Muscle cramps and tremors; tetany; ↓ BP; tingling or numbness of fingers, toes, around the mouth; bronchospasm; carpopedal spasms; ↑ deep tendon reflexes; prolonged QT interval on EKG; positive Chvostek's and Trousseau's signs Inadequate vitamin D consumption, malabsorption disorders, pancreatitis, peritonitis, alkalosis, hypothyroidism or hypoparathyroidism Excess: hypercalcemia Severe constipation, anorexia, nausea, vomiting, polydipsia, lethargy, fatigue, headache, polyuria, ↓ deep tendon reflexes, muscular weakness, bone fractures without trauma, confusion, slurred speech, psychosis, ileus development Prolonged bedrest, excessive ingestion of calcium or vitamin D supplements, excessive serum level of digitalis, cancer, metabolic acidosis Phosphorus Deficit: hypophosphatemia Muscle weakness, bone pain, paresthesia of extremities and around the mouth, stuttering, chest pain, confusion, irregular P, ↑ susceptibility to infection, respiratory failure ↓ K+ or ↓ Mg2+ serum level, vomiting, diarrhea, hyperventilation, burns, hyperparathyroidism, bone disease, diabetic ketoacidosis, alcoholism and alcohol withdrawal, bowel disorders, poor dietary intake Excess: hyperphosphatemia ↑ P, tetany, anorexia, nausea, tingling of fingers and toes, irritability, carpopedal spasms, ↑ deep tendon reflexes, muscle twitching, tetany, seizures, ↓ cardiac output, coma Renal failure, excessive intake of vitamin D or phosphorus, fluid volume depletion, conditions causing breakdown of large amounts of tissue Treatment and Nursing Care Correction of a patient's sodium imbalance must be done slowly and carefully to prevent further damage. Trying to correct sodium levels too rapidly can lead to further swelling or shrinking of cells, especially brain cells. Treatment of hyponatremia involves the administration of additional sodium, either orally, via nasogastric tube, or intravenously. Mild hyponatremia is often remedied with consumption of foods with high sodium content. If the patient is unable to absorb fluids via the digestive tract, the physician probably will order an isotonic IV fluid such as 0.9% sodium chloride or lactated Ringer's solution. You will need to assess vital signs, noting hypotension and increased pulse rate or weakening pulse volume. Monitor intake and output, evaluating balance. If the patient has orthostatic hypotension, assist with ambulation to prevent injury or falls. Always use normal saline 0.9% for nasogastric tube irrigations. If a physician orders tap-water enemas, restrict the number of enemas to one. If more than one is required, such as bowel preparation for a procedure or surgery, consult with the physician regarding use of normal saline to prevent electrolyte problems. If hyponatremia is severe, assess the patient for signs and symptoms of increased intracranial pressure (Box 29-5). An extreme case of hyponatremia may require infusion of a hypertonic IV solution, such as 3% or 5% sodium chloride, to pull the excess water from the brain. These hypertonic IV fluids are rarely used in general medical-surgical settings because they require constant, stringent observation throughout infusion. Safety: Infusion of hypertonic IV solutions requires extremely close monitoring and generally is carried out in an intensive care unit. For information regarding tonicity of IV fluids, see Chapter 38. These patients may also require supplemental oxygen and antiseizure medications. For the patient with hypernatremia, monitor intake and output to be certain the excess fluid begins to be eliminated. Monitor vital signs for elevated blood pressure and bounding pulse. It is important to teach patients to monitor their dietary sodium intake in an effort to prevent future problems. They should be encouraged to read labels carefully, limit salty snacks, eat fresh foods that have not been cured by salts, and ask about low-salt alternatives when dining out. Box 29-5 Signs and Symptoms of Increased Intracranial Pressure The earlier the signs and symptoms are detected, the better the patient's chance of escaping brain damage and permanent neurological deficits. Observe for even subtle changes in level of consciousness (LOC). Early Sign • Changes in LOC* Late Signs • Rising systolic blood pressure to hypertensive levels† • Widening pulse pressure† • Decreasing pulse rate to bradycardia† • Pupillary changes • Impaired body temperature control by the hypothalamus

filtration

Filtration Filtration is the passage of fluid through a partial barrier separating the fluid from certain particles that are too large to pass through the semipermeable membrane. One place where filtration occurs is between the intravascular and interstitial spaces, where fluid movement is affected by hydrostatic pressure, the force the volume of fluid exerts against the capillary walls. When the fluid volume within the intravascular space increases, so does the hydrostatic pressure. Each time the heart beats, more blood is pumped out of the left ventricle into the systemic circulation, which increases the pressure the blood physically exerts against the walls of the vessels. This pumping action of the heart forces the increased hydrostatic pressure through the arteries, through the arterioles, and into the capillaries, forcing fluid and electrolytes through the capillary walls into the interstitial space but not allowing larger molecules such as albumin to leave the intravascular space. The end result is the filtration of fluid from the intravascular space into the interstitial space, which, if excessive, results in edema. Movement of Absorbed Water From the Gastrointestinal Tract When you drink a glass of water, the water you swallow passes through the esophagus and into the stomach. The bloodstream absorbs some of the water from the stomach and small intestine, but most of the water is not absorbed until it reaches the large intestine. Approximately 80% of the volume of water entering the first section of the large intestine, the cecum, is absorbed there. The water molecules must cross through the intestinal wall and capillary wall to enter the bloodstream. Once the water has entered the bloodstream, it becomes part of the plasma and is circulated throughout the vasculature until it reaches the capillary beds, where semipermeable capillary walls allow passage of necessary fluid, required nutrients, and oxygen from the intravascular to the interstitial spaces. This is the same place where carbon dioxide and other waste products are diffused from the interstitial fluid across the capillary wall into the bloodstream to be carried away and removed from the body. Hydrostatic pressure pushes plasma out of the vascular space and across the capillary wall, into the interstitial space where the fluid is now known as interstitial fluid or tissue fluid, which differs from plasma because it does not contain blood cells as does the plasma. This fluid normally moves in and out of the vascular space to maintain a balance. Waste products from the cells travel via the interstitial fluid into the bloodstream to the kidneys, where the waste products can be filtered out into the urine. Depending on the concentration of solute and the degree of osmosis, the fluid in the interstitial space may or may not be moved across another membrane, the cell membrane, into the cell's intracellular space. If the concentration of solute is higher inside the cell than outside, osmosis will cause fluid to move from the interstitial spaces across cell membranes into the cells to dilute the higher concentration of solutes and maintain a balance of fluids and electrolytes. This can result in swelling of cells if too much water is moved inside the cells. If the concentration of solute is higher outside the cells in the interstitial spaces, osmosis will cause water to move from the intracellular space across the cell membrane into the interstitial spaces in an attempt to dilute the solute concentration, resulting in edema. The movement of fluid also occurs in the opposite direction as intracellular fluid is drawn from the cell through the cell membrane into the interstitial space, and then once again into the intravascular space inside the capillaries. These movements of fluid are effected by various pressure processes, including the hydrostatic pressure from blood pressure and osmotic pressures from solute dissolved in fluid. The goal of all the fluid movement back and forth between water compartments is to maintain constant relative proportions of fluid and solutes. This means that if the water is balanced on both sides of a semipermeable membrane, then the electrolytes also are balanced, known as fluid and electrolyte homeostasis. Abnormal Movement of Fluids When, for some reason, the body is unable to maintain fluid and electrolyte balance, normal fluid-moving processes are impaired. One of the possible results of this imbalance is third-spacing of fluids, meaning the fluids are shifted to areas where they can no longer contribute to fluid and electrolyte balance between ICF and ECF. The fluids are still within the body, but they are unavailable for normal use. For example, when excessive fluid has moved into the interstitial space, which often occurs with severe congestive heart failure, edema results. Another example includes liver diseases that result in increased blood pressure in the portal circulation, or the circulation that supplies the liver with blood. The fluid is forced out of the circulation and into the peritoneal cavity, where it is no longer available for use by the body. The diseased liver fails to produce adequate levels of protein to maintain oncotic pressure within the blood plasma, allowing excessive volumes of fluid to leave the intravascular space and move to the interstitial space. This third-spacing of fluid results in edema and ascites, a large collection of fluid within the peritoneal cavity. The effects of third-spacing include the following: • Lowering the volume of the blood, thereby lowering the blood pressure • Increasing the volume of fluid in the interstitial spaces, thereby possibly causing excessive edema, which can result in compression of nerve endings, capillaries, and cells • Lowering the solute concentration of the interstitial fluid, thereby causing excessive amounts of water to move into the cells, resulting in overhydration and possible rupture of the cells, better known as cellular death Knowledge Connection

functions of water in the body

Functions of Water in the Body Water is required by the body for various functions, including the following: • Maintaining temperature: Water helps to maintain body temperature, whether warm or cold. Because it takes longer for the temperature of liquid to change than it does for solid matter, the body's water protects from extreme changes. For example, when you step out of a warm house into a blizzard, your body fluids help to preserve heat. When the body is overheating, evaporation of fluid from sweat and from breathing will keep the body cool. Of course, there are limitations to this ability. Water can only help the body to preserve heat for a certain length of time, depending on factors such as the clothing a person is wearing. Also, water's ability to cool the body can deteriorate when the body becomes dehydrated after large amounts of sweat are lost and not replenished. Safety: When patients are dehydrated, they can lose the ability to regulate their own temperature. • Transporting electrolytes, minerals, vitamins, and waste products: Water transports electrolytes such as sodium and potassium, minerals such as zinc and copper, and vitamins such as vitamin C and the B-complex vitamins to all the individual cells throughout the body. Water also transports waste products from the cells to the blood so that they can be eliminated in the urine. • Protecting the brain and spinal cord: Water, as a component of spinal fluid, acts as a cushion for organs such as the brain and spinal cord, protecting these organs from damage from outside forces. • Lubricating the joints and digestive tract: As one component of synovial fluid, water helps to lubricate joints such as the knees and elbows, reducing friction and allowing for smoother movement. It also provides for the smooth passage of food through the digestive tract, from the mouth through the large intestine. Knowledge Connection Explain four functions of water in the body. Regulation of Body Fluids The most important factor determining water intake is thirst. The hypothalamus in the brain receives information from osmoreceptors, which are receptors that are able to detect when there is an elevated concentration of solutes in the blood, increasing the blood's osmolality, or plasma concentration. Increased osmolality results in low fluid levels. When the hypothalamus detects these conditions, it stimulates thirst. However, if there is too much fluid or if there is a problem with the osmoreceptors, the body will not stimulate thirst. Water Intake As you learned in Chapter 23, the average adult needs to consume somewhere between 1440 and 1920 mL of water per day. Depending on lifestyle and activity, some individuals may need larger water intakes, such as pregnant or nursing women, those individuals who work or exert in extremely hot environments, and athletes. The body can also make 100 to 300 mL of water per day from hydrogen (H+) and oxygen (O2). Body Composition Fatty tissue contains less water than muscular tissue, thus allowing body composition and size to influence the volume of water carried by the body. Men, who typically are more muscular than women, tend to have a higher percentage of body weight due to water. Obese individuals and elders, who commonly have lost much of their muscle mass, have a lower percentage of body fluid than do younger and leaner individuals. Hormonal Regulation Several hormones work to keep fluid in the body and to produce an appropriate volume of urine output. Antidiuretic hormone (ADH) and aldosterone both work on the kidneys to decrease urine production and increase body fluid level. Atrial natriuretic factor (ANF) causes the kidneys to excrete more urine to decrease the body fluid level. Antidiuretic Hormone The hypothalamus produces antidiuretic hormone, also known as vasopressin, which is stored in the posterior pituitary gland to be released as needed. When the osmoreceptors that are located within the hypothalamus are able to detect increased osmolality of the blood, the hypothalamus stimulates the posterior pituitary to release more antidiuretic hormone (ADH). Antidiuretic hormone directs the kidney tubules to increase water reabsorption independently of solids, which helps to dilute the concentration of the blood. This suppression of volume of urine production results in a more concentrated urine. Therefore, ADH probably plays the most significant role in determining whether the urine that is excreted is dilute or concentrated. Aldosterone When kidney baroreceptors (Box 29-2) sense a low blood volume flowing through the kidneys, the kidneys release an enzyme known as renin. Renin begins a cascade of enzyme-induced conversions, the end product of which stimulates the adrenal cortex to produce its primary mineralocorticoid called aldosterone. Aldosterone regulates fluid and electrolyte balance by stimulating the kidneys to retain more sodium and excrete potassium. By increasing the amount of sodium that is reabsorbed, the water reabsorption naturally increases. Remember: Where sodium goes, water follows. This retention of water increases the blood volume and raises blood pressure. Figure 29-3 presents a more detailed description of this cascade of conversions. Atrial Natriuretic Factor When baroreceptors in the vena cava and atrial chambers of the heart detect too much pressure, meaning there is excessive blood volume, the atrium produces atrial natriuretic factor (ANF). This hormone inhibits renal secretion of renin, which interferes with the cascade of hormones that increases sodium and water retention by the kidneys. The kidneys proceed to excrete more sodium, and this increase in sodium causes more fluid to be lost. The end result is increased urinary production and a decrease in the level of body fluids, which also lowers the blood pressure. Normal Fluid Losses The most obvious ways in which the body loses fluid is through elimination of urine and feces. Fluid losses through excretion of urine are controlled by ADH, aldosterone, and the extent of insensible fluid loss. Insensible fluid loss is that which cannot be directly measured, such as fluid lost during respiration and perspiration. Normal fluid loss for healthy patients varies from about 1 to 3 L/day, depending on fluid intake (Table 29-1). Box 29-2 Baroreceptors A baroreceptor is a sensory nerve ending that detects, or is stimulated by, changes in pressure due to the blood volume. Another term for baroreceptor is pressoreceptor. These receptors are located in the atrial walls of the heart and in the inferior and superior venae cavae, as well as in the aorta and the carotid sinus located at the base of the internal carotid artery. When pressure changes are detected, the baroreceptors send a message to the central nervous system to either increase or decrease arterial diameter and increase or decrease heart rate.

role of kidneys

In relation to acid-base balance, the kidneys have the ability to perform four basic functions as needed to assist in maintaining the proper blood pH: 1. Retain hydrogen (H+) 2. Excrete H+ 3. Retain sodium bicarbonate (NaHCO3) 4. Excrete NaHCO3 When the body fluids become too acidic, the job of the kidneys is to remove H+ from the blood and excrete it into the urine to be carried out of the body, and to reabsorb more NaHCO3 back into the blood. Each of these two actions will make the blood less acidic and increase its alkalinity, helping to return the pH back to normal. When the kidneys sense that the blood is too alkaline, they will retain more H+ in the blood to increase the acidity and excrete more NaHCO3 into the urine to further decrease the alkalinity of the blood, once again helping to return the pH back to normal. The kidneys work more slowly than the lungs, changing the pH balance over a period of days rather than hours. However, although they take longer to make pH adjustments, the kidneys are capable of making much more significant changes in the pH than are the lungs, making the kidneys the most effective of the three systems for balancing blood pH. Knowledge Connection Which two body organs are involved in managing acid-base balance? What are the specific functions of each system that affect acid-base balance? Which system works most effectively to make pH adjustments? Acid-Base Imbalance An uncorrected acid-base imbalance will lead to either acidosis or alkalosis. Acidosis means an increase of acids in the blood, which increases the acidity, while alkalosis means an increase in blood alkalinity due to an increase of bases/alkaline substances or a decrease of acids. Normally, there are subtle shifts back and forth in the blood pH between slightly acidotic and slightly alkalotic as situations and conditions change minute amounts; however, the buffer, respiratory, and renal systems are able to accommodate these shifts and, through compensation, bring the blood back to a normal pH. When patients are ill from chronic or acute diseases, sometimes their bodies are unable to respond quickly enough or strongly enough to prevent extreme changes in pH, resulting in additional and possibly more serious health problems. The illness may involve either the pulmonary or the renal system and, by impairing its normal functions, may make the system the actual source of the acid-base imbalance. However, other metabolic problems can cause metabolic imbalances. Some of these problems will be discussed a little later in this chapter. Anatomy and Physiology Connection: The Brain and Acid-Base Balance Chemoreceptors located in the aorta, carotid arteries, and medulla have the capability to sense or detect changes in blood levels of O2 and CO2, as well as disturbances in pH. Upon sensing a lowering pH, meaning increasing acidity, the receptors send a message to the brain indicating that the blood's pH is too acidic. The medulla then signals the lungs to increase the rate of respiration, which will blow off more CO2, helping to reduce the acidity of the blood. Upon sensing a higher pH, meaning increasing alkalinity, the receptors send a message to the brain indicating the blood's pH is too alkaline. The brain then signals the lungs to decrease the rate of respirations, which will allow retention of more CO2 so that it can bond with H2O and make more H2CO3, which can release more H+ ions. This raises the acidity of the blood toward a more normal pH.

magnesium

Like calcium, magnesium (Mg2+) is also part of the bone structure. About 50% to 60% of the body's magnesium is located within bone cells; the rest works to actively assist with the metabolic work of other cells and metabolizing ATP for energy. These include cells of the heart, vascular system, skeletal muscles, nerves, and immune system. Magnesium has a role in activating enzymes and metabolizing protein and carbohydrates. It also helps to lower blood pressure by dilating the peripheral blood vessels and reducing peripheral vascular resistance. New research shows that magnesium can help protect the heart and support the immune system. Magnesium is important for neuromuscular function and is sometimes used by patients who experience twitching and uncontrolled movements of their legs while trying to sleep. The magnesium works at the neuromuscular junctions, producing somewhat of a sedative effect, reducing the excitability and twitching of the muscles. It also serves to depress the central nervous system. To maintain an appropriate blood level and prevent deficiency, the Food and Drug Administration (FDA) recommends a daily intake of 400 mg magnesium (see Table 29-2). Magnesium Imbalances: Deficiency and Excess Hypomagnesemia refers to a blood level of magnesium that is below the normal range. It is believed that most Western diets do not contain enough magnesium. Although hypomagnesemia may not cause severe symptoms, over time it can have a negative effect on the individual's overall health. In general, low levels of magnesium will increase nervous system irritability and muscular contractility. Patients with alcoholism frequently develop hypomagnesemia along with other nutritional deficiencies. When an individual with alcoholism experiences alcohol withdrawal, treatment commonly requires IV infusion of glucose as well as other nutrients in which the patient is deficient. Administration of glucose will cause magnesium to shift back into the cells, further worsening of the low magnesium blood level. This makes it necessary to provide either oral or IV magnesium supplementation along with the glucose and other nutrients. A high level of magnesium, known as hypermagnesemia, will slow the nervous system responses, including the respiratory rate, and generally depress neuromuscular junctions. Hypermagnesemia may be caused by adrenal or thyroid gland disease, excessive use of magnesium-containing antacids or laxatives, or hypothermia. However, the two most common sources of excess magnesium are diabetic ketoacidosis and kidney failure. During ketoacidosis, when fat and protein, rather than glucose, are broken down for energy, intracellular magnesium is moved outside the cells into the intravascular spaces, raising the blood levels. When kidney functions are impaired, they do not remove adequate levels of magnesium from the blood, leaving a higher than normal blood level (see Table 29-3). Treatment and Nursing Care Both deficient and excessive levels of magnesium are closely linked to potassium and calcium imbalance. Therefore, when one imbalance is present, you will want to assess for the same imbalance in the other two electrolytes, because returning magnesium levels to normal will require treatment of the imbalance of these other electrolytes. Hypomagnesemia can be treated with oral magnesium tablets if the deficiency is not too severe. With critically high levels of magnesium, IV calcium may be given, and diuretic medications or dialysis may be ordered to promote excretion of magnesium. Patients with hypermagnesemia should be assessed for use of over-the-counter antacids and laxatives containing magnesium, as well as their knowledge of other methods of maintaining bowel regularity.

fluid volume excess

Most fluid volume excess, also known as hypervolemia, is caused by retention of sodium and water in the ECF spaces. This may be due to intake of dietary sodium, administration of IV fluids containing sodium, or retention of sodium or fluid as a result of medication or kidney, heart, or liver disease. However, the result is the same for all these causes: decreased urinary output and expansion of fluid volume within the intravascular and interstitial spaces. In rare cases, a patient may develop excessive thirst, or polydipsia, related to various medical conditions such as diabetes mellitus, diabetes insipidus, or mental illness. This can result in ingestion of tremendous volumes of fluid, even several thousand milliliters. Retention of fluids may occur due to the poor pumping mechanism of congestive heart failure, which reduces cardiac output and kidney perfusion. Renal failure with decreased glomerular filtration rate can result in inadequate excretion of urine. Infants, small children, frail elders, and patients with congestive heart failure or renal failure are more susceptible to fluid overload than average adult patients. Fluids administered orally or intravenously may place the patient in fluid overload and cause serious problems if the health-care provider is not alert to the signs and symptoms of fluid overload. Knowledge Connection What is generally the etiology of a fluid volume excess? What type of patients are considered more susceptible to fluid overload problems? Assessment and Diagnostic Findings For patients at risk for or with a known diagnosis of fluid volume excess, assess the renal and digestive systems as well as the respiratory and cardiovascular systems (Box 29-4). Diagnostic test results supporting fluid volume excess may include: • Low hemoglobin or hematocrit due to hemodilution • Low urine specific gravity due to dilution • Fluid or pleural effusion noted on chest x-ray • Low partial pressure of oxygen in arterial blood (PaO2) in arterial blood gases (ABGs) • Decreased BUN due to hemodilution • Decreased sodium or other electrolytes due to hemodilution Box 29-4 Possible Assessment Findings Related to Fluid Volume Excess Signs and symptoms of fluid volume excess may appear suddenly. Assess the potential of each patient receiving IV fluids for medical history or current conditions to identify if the patient might be at risk for fluid volume excess. Monitor intake and output, auscultate breath sounds, and evaluate vital signs of all patients receiving IV fluids. • Increased respiratory rate, shortness of breath with exertion, or labored respirations • Sudden onset of coughing • Jugular vein distention • Increased blood pressure, pulse pressure, or central venous pressure • Full, bounding pulse • Edema of extremities or dependent areas, such as sacrum • Auscultation of rales or wheezes, and muffled or distant heart sounds • Weight gain • Increased urine production in an attempt to rid body of excess fluid • Pink or frothy sputum • Decreased oxygen saturation level • Anxiety or fear that is unexplainable by the patient • Ascites (distention of the abdomen due to fluid collection in the peritoneal cavity) Knowledge Connection Name at least eight signs and symptoms of fluid volume excess. What diagnostic test results might support this diagnosis? Treatment and Nursing Care You should carefully monitor intake and output in both acutely and chronically ill patients who have been diagnosed with fluid volume excess or who are at risk for the disorder, including those receiving tube feedings and those who have IV fluids infusing. Administer ordered diuretics and monitor for effectiveness. Assess daily weights at the same time of the day, preferably before breakfast, using the same scales and with the patient wearing the same type of garment. A low-sodium diet may be ordered to restrict dietary intake of sodium, or the patient may be instructed to avoid adding salt to food. Monitor meal trays to ensure there are no extra salt packets or high-sodium foods. If the physician has ordered fluid restriction, determine the volume of fluid allowed on each shift and monitor it closely. Post the volume of fluids allowed for each shift above the patient's bed or on a marker board to serve as a reminder for patient, family, and staff. Collaborate with the dietary service to limit fluids sent on meal trays. Provide patient and family teaching to ensure understanding and cooperation with intake and output, documentation, and ingestion of sodium and fluids. Assess vital signs, including oxygen saturation by pulse oximetry (SpO2), every 4 hours unless severity requires more frequent assessment. Monitor for elevated blood pressure, increased pulse rate and volume (especially bounding pulse), and elevated temperature. Auscultate breath sounds and heart sounds at least every 4 hours, noting adventitious, decreased, or absent breath sounds and muffling of S1 and S2. Assess the abdomen for ascites and the extremities and dependent body sites (such as the sacrum) for edema. Monitor urine output every 2 to 3 hours, or evenly hourly if inadequate urine excretion is suspected. A continuous indwelling Foley catheter must be in place if you need to monitor hourly output. Monitor laboratory and x-ray results as previously mentioned. It usually is necessary for the physician to order one or more diuretics. Safety: Some diuretics such as furosemide, a loop diuretic, are known to deplete the serum level of potassium, making it necessary that you monitor the laboratory results for changes in potassium level. If the potassium level drops below normal, supplemental potassium will have to be administered. If the patient has respiratory difficulties, supplemental oxygen can be ordered. Severely impaired renal function that does not respond to diuretics and standard treatment may require dialysis to remove the waste products along with the excess sodium and fluid. Knowledge Connection Describe the basic assessments you should make when fluid volume excess is suspected or diagnosed. What nursing interventions would be appropriate for fluid volume excess? Patient Teaching Connection: Furosemide Many patients are prescribed diuretics to assist with elimination of excess fluids. Patients often call these drugs their "water pills." Some types of diuretics, such as osmotic diuretics, cause the patient to lose potassium and sodium. Furosemide (Lasix), a common osmotic diuretic, can also cause magnesium and calcium losses. Because hypokalemia is common when patients take daily furosemide, the physician may also prescribe extra dietary potassium or potassium supplements. According to the Institute of Medicine (IOM), adequate intake of potassium for adults is 4700 mg/day. Most patients will take 20 milliequivalents (mEq), equal to about 1500 mg/day (10 mEq is equal to 750 mg), and will receive the rest of their potassium intake through their diet. Teach your patients taking furosemide to follow up for their blood work as ordered. It is very important that electrolyte levels be checked regularly. Encourage patients to eat foods high in potassium, such as bananas, which provide about 500 mg of potassium each. Other foods high in potassium include yellow and orange fruits such as oranges and apricots, avocados, baked potatoes, sweet potatoes, yogurt, white beans, and halibut

osmosis

Osmosis The membranes that form the various fluid compartments include the vessel walls that hold the blood within the vasculature and the cellular membranes that contain the cell's contents. These membranes are described as semipermeable, which means they allow passage of certain substances, but not all. Body fluids consist of a water-based solvent and various particles of solute, substances that will dissolve in the solvent. The number of solutes present in the solvent determines the fluid's osmolality or concentration. When a difference in osmolality exists in the fluid on two sides of a semipermeable membrane, the body's homeostatic mechanisms kick into action in an attempt to balance those differences. Osmosis is the process in which water moves through a semipermeable membrane from the side where the fluid is lowest in solute concentration to the side where the fluid is highest in solute concentration (Fig. 29-1). The goal of osmosis is to balance out the two fluid concentrations until they are equal on both sides of the membrane. This could be the difference between the concentration of the blood within a capillary and the concentration of the interstitial fluid outside of the capillary in the interstitial space, or it could be the difference between the concentration of the cellular fluid and the concentration of the interstitial fluid on the other side of the cell membrane. Figure 29-1 Osmosis is the movement of water across a semipermeable membrane from the less concentrated solution to the more concentrated solution. The purpose is to dilute the more concentrated solution to equal that of the lesser concentrated solution. (From Wilkinson JM, Treas LS. Fundamentals of Nursing: Theory, Concepts & Applications, Vol. 1, 2nd ed. Philadelphia: FA Davis; 2011.) Knowledge Connection Which does osmosis move: water or solute? To envision this process, picture a clear container that is divided down the middle by a semipermeable membrane that will allow water to pass through but not solute. On each side of the membrane, there are 8 ounces of water. You pour 4 ounces of table salt into the water in the right side, but only add 1 ounce of salt to the water in the left side. Now the fluid on the right side has a great deal more solute, making it much more concentrated than the water on the left side. The difference in the solute content would cause the less dense water on the left side to permeate through the membrane into the right side until the two concentrations were equalized on both sides. Osmotic pressure is the amount of power that is exerted by the concentration of solutes, such as sodium chloride, which works to prevent water from moving out of the specific compartment. Because the osmotic pressure of the fluid on the right side is greater due to the higher concentration of solutes, it prevents the water from flowing out from the right to the left side. This same increased concentration of solutes draws or pulls the water through the semipermeable membrane (osmosis) in an attempt to effect dilution of the right side. Blood plasma is the liquid portion of the blood that remains after removing the blood cells. It is approximately 90% water and normally contains plasma proteins that are too large to pass through the semipermeable capillary walls. An important function of the primary plasma protein albumin is to assist in the maintenance of fluid balance within the intravascular spaces. Albumin works similarly to solutes, such as electrolytes, in that the higher the concentration of albumin, the greater the osmotic pressure in that particular compartment. When we refer to the osmotic pressure exerted by and related to the albumin level of the blood plasma, it is termed the oncotic pressure. When an increased concentration of waste components, such as glucose or contrast dye, is excreted into a patient's urine, the increased osmotic pressure will draw an extra volume of water with it to be eliminated. This is known as osmotic diuresis. Box 29-1 presents an example of an osmotic diuretic.

oxygen

Oxygen is your body's number one requirement to sustain life, with food, water, and physical safety following in close order. In this chapter, you will learn why water is the second most critical substance for sustaining life. You will learn that, wherever you find water within the body, you will also find substances called electrolytes. You also will learn about the forces and processes that regulate the movement of water and electrolytes, as well as the role they play in maintenance of the body's acid-base balance. Then you will learn how to apply this information to care for patients who have disturbances of acid-base or fluid and electrolyte balance. Water Water normally accounts for 50% to 70% of the body's total weight and serves as the liquid in which the body's solid components are dissolved. Age affects the percentage of water that comprises total body weight. For example: • Adult males: 60% to 65% • Adult females: 55% to 60% • Older adults: 50% to 55% • Children: 50% to 55% • Full-term infants: 65% to 70% • Premature infants: 65% to 80% Within the body, the lungs are composed of approximately 90% water while the brain is 70% water. Each individual's blood is 80% to 83% water. Safety: The body has such a high requirement for water that fluid losses can interfere with homeostasis and impair certain bodily functions to such an extent that an individual can only survive a few days without water intake. Knowledge Connection What percentage of body weight is made by water in the following age groups: Newborns? Adult males? Older adult females? Teenagers? Adult females? What is the most important to survival: water or food? Distribution and Movement of Body Fluids Body fluids reside in one of two water compartments: intracellular space or extracellular space. In healthy patients, approximately two-thirds of body fluids reside inside of the individual cells, which are individual living units that require their own water, nutrients, and oxygen. Cells comprise the water compartment, which holds intracellular fluid (ICF). The other one-third of the body's fluid is located in the compartments outside the cells; this fluid is known as extracellular fluid (ECF). The extracellular compartment is further divided into two main spaces: the interstitial space and the intravascular space. The interstitial space is that space surrounding and between cells, which holds fluid known as either tissue fluid or interstitial fluid. Lymph fluid is also considered to be part of the interstitial fluid. The intravascular space includes the blood vessels and the heart and holds the plasma. ECF also includes the cerebrospinal fluid surrounding and cushioning the brain and spinal cord, specialized fluids such as aqueous humor within the eye chambers, and synovial fluid that lubricates joints. However, because these fluids constitute such a small percentage of the ECF, we do not include them when we are discussing fluid and electrolyte balance. Even though fluids are distributed within the interstitial space and the intravascular space, they are never static. Fluids are continually moving across membranes to other compartments in an effort to maintain equilibrium between the compartments. This movement of fluid is controlled by several processes, including osmosis, diffusion, and filtration, all of which are partially related to fluid volume. The volume of fluid is directly affected by the amount of water ingested and absorbed from the gastrointestinal (GI) tract. Fluid volumes are very closely related to the concentration of the molecule sodium chloride, also know as table salt. If individuals take in or retain too much sodium chloride, they will also retain excess water. Water will travel back and forth between ICF spaces and ECF spaces depending on where there is more sodium chloride. One way to think of it is where sodium goes, water follows. That is why, after eating a large bag of buttered, salted popcorn, you find yourself thirsty and drinking lots of liquids. The fluid inside cells is called the cytoplasmic matrix and contains about 70% water. The concentration of certain elements inside of cells is much higher than that outside of cells. The electrolyte potassium and protein molecules are found in much higher concentrations inside of cells than outside of cells, whereas sodium, chloride, and bicarbonate normally occur in higher concentrations outside.

potassium

Potassium (K+) is represented by the letter "K" because of its ancient name, Kalium. It is the most abundant cation in the ICF. Potassium functions in transmission of nerve impulses and muscle contraction. It assists in building proteins and muscles as well as in the breakdown of carbohydrates. It contributes to the osmolarity of body fluids, therefore playing a major role in keeping fluids inside of cells. Although 3.5 to 5.3 mEq/L is considered to be the normal serum range for potassium, some physicians prefer to keep the serum potassium above 4.0 mEq/L in patients with heart problems to reduce risk of arrhythmias. The IOM reports that most people who follow a typical Western diet take in the minimum amount of potassium but do not eat enough to stay in optimum health. The IOM now supports the idea that dietary intake of 4.7 g/day may decrease long-term health problems (see Table 29-2). Potassium Imbalances: Deficiency and Excess Hypokalemia is defined as a potassium level that is below the normal range, and hyperkalemia is an elevated level. Hypokalemia can cause muscle weakness and tetany, or severe muscle spasms. Safety: More importantly, because potassium is a key electrolyte in controlling nerve transmission of the electrical impulses that cause the heart to contract, both low and high levels of potassium can affect the heart rhythm and cause life-threatening arrhythmias. In patients with renal failure, kidney functions become impaired and the kidneys do a poor job of filtering out excess potassium, which raises the serum potassium level. (See Table 29-3 for further information regarding potassium imbalances.) Treatment and Nursing Care In patients with hypokalemia, low levels of serum potassium can be increased with supplemental potassium chloride (KCl) as oral tablets, liquids, powders, or IV formulations. A patient who routinely takes medications such as furosemide, a diuretic that increases excretion of sodium, potassium, and water volume in the form of increased urination, is likely to take a daily oral dose of potassium in order to prevent hypokalemia from occurring. Hyperkalemia must be treated to prevent problems. In some cases, a patient may require emergency treatment for a dangerously elevated level of potassium. This may include administration of medications such as sodium polystyrene sulfonate (Kayexalate), which binds with potassium and stimulates potassium elimination through stools. For treatment of hyperkalemia in patients with impaired renal function, it is common to restrict the dietary intake of potassium-rich foods such as potatoes. It is your responsibility to monitor the serum potassium levels of all your patients, but be especially mindful of the serum potassium levels in a patient who: • Is vomiting or having diarrhea • Has a nasogastric tube to suction • Is suffering from malnutrition or dehydration • Is taking osmotic diuretics • Has renal disease In severe hyperkalemia, it may also be necessary to administer IV glucose and insulin to help drive potassium back into the cells. Safety: KCl is never administered by IV push or intramuscularly. Because of a high potential for death associated with IV potassium, most institutions require that it be mixed into a diluted IV solution by the pharmacy and then be double-checked by the nurse before it is administered to the patient. It should be administered over several hours at the preferred rate of 10 to 20 mEq/hr. The infusion rate should never exceed 40 to 60 mEq/hr. Safety: When KCl is added to a 1000-mL bag of solution, the KCl will concentrate at the bottom of the bag of IV solution. Agitate the solution well before infusing. Real-World Connection: The Dangers of Potassium Chloride Potassium chloride is a dangerous drug—so dangerous, in fact, that in some states it is used for death-by-injection death penalties—which is why it is so very important to be careful when administrating it to a patient. The following story illustrates just how careful you should be: A student nurse on a medical-surgical clinical was administering medications. One of the patients was scheduled to receive a daily dose of potassium chloride (KCl) via the IV route. After the student read the order, she interpreted the order to mean IV push, which means to inject the drug directly into the IV line over a couple of minutes, rather than to dilute the KCl in a 1000-mL bag of IV solution and infuse it over several hours. The student administered the KCl via direct IV push. The concentrated dose of KCl interrupted the electrical conduction in the patient's heart. The patient arrested and died. This tragic but true event could have been prevented by using basic safety measures. Always make certain you are familiar with any medication you are going to administer, no matter what it is: over-the-counter or prescription, narcotic or vitamin supplement, or electrolyte. If you are not familiar with the specific medication, look it up in your drug reference book, always. Safety: When administering an electrolyte in less than 1000 mL of fluid via the IV route, a second nurse should be asked to double-check and confirm the prepared medication, route, and rate of administration before administration.

imbalances

Respiratory Imbalances Respiratory conditions and disease can create either alkalosis or acidosis. If an illness causes a patient to breath too rapidly or too deeply, the effect will be excessive loss of CO2, thereby decreasing the acidity of the blood. If the condition continues, it results in excessive alkalinity, which raises the blood pH above 7.45 and is known as respiratory alkalosis. If disease processes make a patient unable to take deep breaths, decrease the rate of respirations, or somehow interfere with the exchange of CO2 and O2 gases, excessive CO2 will be retained, causing the blood's pH to become increasingly acidic. If allowed to continue until the blood pH is sufficiently acidic and the pH drops below 7.35, a condition known as respiratory acidosis results. When the lungs are the source of either acidosis or alkalosis, the kidneys do what they can to compensate for the impaired lungs (Box 29-7). Metabolic Imbalances Metabolic diseases that cause excessive loss of H+ or excessive gain of bicarbonate can result in an elevated pH above 7.45, known as metabolic alkalosis. Severe vomiting and nasogastric suctioning are two of the most common causes of metabolic alkalosis, both due to loss of potassium (K+) and hydrochloric acid (HCl) in the gastric juices. HCl contains hydrogen and chloride, so the loss of this acid contributes to development of alkalosis. Box 29-7 Compensation for Respiratory and Metabolic Acid-Base Imbalances The renal system (kidneys) and the respiratory system (lungs) work together, along with the buffer system, to compensate for each other's impaired functioning during illness or injury. If one system's impairment causes acidosis, the other system will perform its part to "get rid" of components that it can control that would contribute to further acidosis. If one system is impaired in such a manner that it results in alkalosis, the other system will do whatever it can to get rid of the components that it controls that would further contribute to the alkalosis. These compensatory actions are as follows. • If the lungs cause respiratory alkalosis: The kidneys retain H+ and excrete NaHCO3 into the urine to decrease alkalinity and increase acidity of the blood. • If the lungs cause respiratory acidosis: The kidneys retain NaHCO3 and excrete H into the urine to decrease acidity and increase alkalinity of the blood. • If any metabolic condition causes metabolic alkalosis: The lungs retain CO2 to decrease alkalinity and increase acidity of the blood. If the kidneys are NOT the source of the imbalance, they will conserve H and excrete NaHCO3 into the urine to increase acidity of the blood. • If any metabolic condition causes metabolic acidosis: The lungs increase respiratory rate/depth to blow off more CO2 to decrease acidity and increase alkalinity of the blood. If the kidneys are NOT the source of the metabolic imbalance, they will conserve NaHCO3 and retain H+ to decrease acidity and increase alkalinity of the blood. The loss of gastric K+ contributes to alkalosis in two ways. Loss of gastric K+ due to vomiting or suction causes decreased absorption of K+ from diet, which results in hypokalemia. When the blood level gets low, it causes intracellular K+ to move out of the cells and into the blood in an attempt to maintain adequate blood levels. When a cation leaves the cells, it must be replaced by another cation to maintain neutrality of electrical charges, so H+ is moved into the cells. Hypokalemia also stimulates the kidneys to conserve K+ and excrete H+, causing further loss of acid. Other situations that can give rise to metabolic alkalosis include long-term use of a diuretic such as furosemide, which causes K+ loss in the urine; a gastrostomy tube draining gastric contents; or administration of excessive amounts of sodium bicarbonate during resuscitative efforts. Diseases that can cause metabolic alkalosis include Cushing's syndrome and hyperaldosteronism because they cause abnormal electrolyte metabolism. Metabolic acidosis is the condition of excessive H+ concentration or an excessively low level of bicarbonate that is caused by a metabolic disease or condition that results in a pH below 7.35. Diseases and conditions that affect the lower intestinal tract and result in excessive losses of bicarbonate, such as diarrhea, ulcerative colitis, and surgical colectomy, all serve as common causes of metabolic acidosis. Renal failure reduces the kidney's ability to adequately filter wastes and excess electrolytes from the blood. This can cause hyperkalemia, elevated blood levels of creatinine, and excessive H+ retention and can result in metabolic acidosis. Any cardiovascular diseases that impair blood flow to the kidneys can lead to varying degrees of renal failure and metabolic acidosis as a result. Critical levels of metabolic acidosis can occur rapidly due to changes in the cell's metabolism related to a diabetic crisis, alcohol or medicine poisoning, crushing bone injuries, or burns. Compensation by the Lungs The respiratory system responds quickly to minute changes in pH and works very rapidly, continuously adjusting as needed to help balance the pH, but it is only capable of making small adjustments in the pH. When a larger pH adjustment is required, especially for a longer period of time, the lungs' ability to compensate will be limited, and they will require the assistance of the kidneys to return the pH to normal ranges (see Box 29-7). Treatment and Nursing Care for Acid-Base Imbalances Because various respiratory illnesses can cause pH imbalance, it is key that you understand the pathophysiology of the disease process causing the problem. If you do not understand how the disease changes either the structure of the respiratory system or the way that the system functions, you will not understand what you must do to intervene and correct the problem. Monitor vital signs for tachypnea and bradypnea, tachycardia, and fever. Assess characteristics of the patient's respirations, including depth and pattern, dyspnea, length of inspiration versus expiration, use of accessory respiratory muscles, and level of difficulty. Are there substernal or costal retractions? Assess skin, mucous membranes, and nailbeds for cyanosis. Assess O2 saturation and need for supplemental O2. Monitor laboratory results of arterial blood gases (ABGs). Seriously ill patients may require endotracheal intubation and mechanical ventilation. In Chapter 28, you were introduced to the laboratory diagnostic test called arterial blood gases (ABGs). See Table 28-2 to review the normal ranges for ABGs and the significance of abnormal levels. Box 29-8 provides steps to follow while interpreting ABG results, with examples. Knowledge Connection Which two body systems are key in managing acid-base changes? What functions can each of these organs perform in efforts to maintain acid-base balance? Explain at least two causes of metabolic acidosis and two causes of metabolic alkalosis.

abg interpretation steps

Arterial Blood Gases Interpretation Steps Arterial blood gas (ABG) results are useless you understand what they mean. Interpretation of arterial blood gas results must be done systematically, following the steps below closely and in the order they are presented. It is important to understand each step and be able to apply the information, not just regurgitate the normal ranges of the various components. Begin by evaluating the pH, followed by the PCO2 (referred to as CO2 in the rest of this box), and then the HCO3-. After having evaluated all three components, you should be able to determine whether there is an imbalance and, if so, which system caused the problem and whether there is compensation or not. Normal ranges: pH = 7.35-7.45 CO2 = 35-45 mm Hg HCO3- = 22-26 mEq/L CO2 is considered an acid. HCO3- is considered a base, or alkaline. If the pH is below 7.35, it is acidic. If the pH is above 7.45, it is alkaline. If the CO2 is elevated, it will increase acidity, and if it is below normal, it will increase alkalinity. If the HCO3- is elevated, it will increase alkalinity, and if it is below normal, it will increase acidity. Both systems will attempt to compensate for any deviations from normal that the other system might have made. 1. View the pH result and determine whether it is within normal limits, acidotic, or alkalotic. 2. Analyze the CO2: Is it within normal limits; elevated, meaning acidosis; or low, meaning alkalosis? 3. Analyze the HCO3-: Is it within normal limits; low, meaning acidosis; or elevated, meaning alkalosis? 4. If all three are within normal range, you have normal ABGs. 5. If the pH shows acidosis: Determining which of the CO2 (lungs) or HCO3- (kidneys or other metabolic process) values also indicates acidosis should identify the source of the imbalance. Examples: a. pH=7.30, CO2=48, HCO3- =26: The lungs have retained excessive CO2 (acid); now pH is acidic (= respiratory acidosis). b. pH=7.30, CO2=44, HCO3- =20: The kidneys excreted extra HCO3- (base) and retained too much H+ (acid); now pH is acidic (= metabolic acidosis). c. pH=7.49, CO2=31, HCO3- =23: The lungs have blown off excess CO2 (base); now pH is alkalotic (= respiratory alkalosis). d. pH=7.49, CO2= 41, HCO3- = 30: The kidneys have retained extra HCO3- (base) and excreted extra H+; now pH is alkalotic (= metabolic alkalosis). 6. If both lungs and kidneys indicate they are the source of alkalosis (or acidosis): Both respiratory and metabolic alkalosis (and acidosis) are present. Example: pH=7.30, CO2= 49, HCO3- =19 The lungs retained too much CO2 (acid); the kidneys retained too much H+ (acid) and excreted too much HCO3- (base). Therefore, pH= acidic, CO2=acidic, and HCO3- =acidic, giving you respiratory acidosis and metabolic acidosis. 7. If one system is the cause of the imbalance: If the lungs, for example, have caused acidosis by retaining too much CO2 (acid), but the kidneys have really worked at compensating by getting rid of as much H+ (acid) and retaining as much HCO3- (base) as possible, the end result is that the kidneys may successfully bring the pH back to normal range, even if it is only barely within the range. This is known as compensation. Example: pH = 7.45 (close to alkaline end), CO2 = 32 (alkaline), HCO3- = 20 (acidic) The pH is just barely within normal range (close to the alkalotic end). The lungs show evidence of causing the alkalosis by blowing off too much CO2 (acid). This produces CO2 = 32 (decreasing acidity and increasing alkalinity). This indicates that there was respiratory alkalosis; but the kidneys excreted extra HCO3- (base) and retained extra H+ (acid), which increased acidity and decreased alkalinity, bringing the pH back into normal range (just barely). This is known as respiratory alkalosis with compensation.

bicarbonate

Bicarbonate Bicarbonate (HCO3-) is a main anion of the ECF that is controlled by the kidneys. It is also present in lesser amounts in the ICF. Its normal range is 22 to 26 mEq/L. Its primary function is to serve as a buffer in regulating the acid-base balance of the blood. Because bicarbonate is an alkaline buffer, it helps to decrease acidity of the blood. Bicarbonate is not generally consumed in the diet except in minute amounts in the form of sodium bicarbonate, commonly known as baking soda. Therefore, it must be produced by the body. Bicarbonate Imbalances: Deficiency and Excess Because bicarbonate and chloride work together to keep an overall electrical equilibrium, a chloride imbalance can affect the bicarbonate level. Bicarbonate acts as an acid buffer; therefore, deficiencies or excesses can result in acid-base imbalance. Medical treatment and nursing care for bicarbonate imbalances are focused more on resolving the underlying problem that caused the imbalance rather than just correcting the imbalance.

Diffusion

Diffusion is another process that occurs when there is a difference in solute concentration on two sides of a semipermeable membrane. Diffusion can apply to either solute or solvent but is most commonly applied to the solute particles. Diffusion allows a substance to flow over naturally from an area of higher concentration into an area of lower concentration (Fig. 29-2). To envision this process, think about what happens when you pour a colored powdered substance, such as a flavored drink mix colored red, into a clear pitcher of water. The colored particles initially group in a small, bright red, dense pile on top of the water before sinking into the water, making an area of intense bright red just below the water's surface. Then as the particles continue to seep toward the bottom of the pitcher, they begin to spread out to the areas where there are no red particles, coloring the water as they go. Eventually, as the drink mix particles spread evenly throughout the water, the water becomes a lighter, evenly colored red liquid. Box 29-1 Mannitol: An Osmotic Diuretic A highly concentrated sugar alcohol called mannitol is sometimes administered intravenously to patients suffering with increased intracranial pressure, which, if poorly controlled, can result in brain damage. The purpose of the mannitol is to cause osmotic diuresis, which means to increase the osmolality of the blood so that water will be pulled from the interstitial spaces into the intravascular space, where it can then be eliminated by the kidneys. This will lower the fluid content within the brain and thereby reduce the intracranial pressure. Figure 29-2 Diffusion is the movement of solute across a semipermeable membrane from an area of higher solute concentration to the area of lower solute concentration. (From Wilkinson JM, Treas LS. Fundamentals of Nursing: Theory, Concepts & Applications, Vol. 1, 2nd ed. Philadelphia: FA Davis; 2011.) An example of how diffusion is utilized in the body is the exchange of oxygen and carbon dioxide. When you inhale room air into your lungs, it fills the alveoli with air concentrated with oxygen. The capillary that surrounds each alveolus carries venous blood, from which most of the oxygen has been depleted as it was used by the cells in the body, as well as a high concentration of carbon dioxide, the waste product that is left over after oxidation within the tissues. That makes a higher concentration of oxygen molecules on the alveolar side of the alveolar-capillary membrane than on the capillary side. Plus, it makes the concentration of carbon dioxide higher on the capillary side of the alveolar-capillary membrane than on the alveolar side. The more highly concentrated oxygen molecules within the alveoli diffuse across the alveolar-capillary membrane into the capillary blood, where they can bind with hemoglobin and be transported to the cells all over the body. The more highly concentrated carbon dioxide molecules within the capillaries diffuse across the alveolar-capillary membrane into the lungs, where they can be exhaled from the body.

phosphorus

Phosphates are ions of the element phosphorus, but the two names are generally used interchangeably. Phosphate (PO43-) is the primary intracellular anion and is essential to all body tissues, especially red blood cells and muscle cells. Phosphorus is used in the formation of adenosine triphosphate (ATP) and energy exchange by cells, and it serves as part of the acid-base buffering system. Similar to magnesium, 70% to 80% of phosphorus is stored in the bones and teeth. Approximately 10% is located in nerve tissue and another 10% in muscle cells. The phosphorus level is inversely proportional to the calcium level, which means that dropping phosphorus levels in the blood will cause calcium blood levels to rise proportionately and vice versa. A high phosphorus level causes calcium to leave the bloodstream and can cause calcium to be deposited in organs rather than the bones (see Table 29-2). Phosphate Imbalances: Deficiency and Excess When there is a low magnesium level or a high calcium level, you will want to assess for a low phosphorus level, known as hypophosphatemia. Dietary hypophosphatemia is rare because phosphorus is abundant in the Western diet, although a diet that is deficient in vitamin D can decrease blood levels of phosphorus. A severely low level of phosphorus is dangerous for the patient and must be treated as soon as possible. Hyperphosphatemia is the name for excessively high blood levels of phosphorus; few signs or symptoms accompany the elevation. Children generally have slightly higher levels of phosphorus than adults (see Table 29-3). Treatment and Nursing Care Nurses should assess for a history of malnutrition and laxative use, then educate the patient on phosphorus requirements. If phosphorus is chronically high, as in patients with chronic kidney disease, oral medications that will bind phosphorus can be prescribed over a long period. Patients also may be prescribed a low-phosphorus diet. If phosphorus is low, dietary changes or supplements may be ordered; for more severe cases, use of the IV route for replacement is common. However, when administered via the IV route, phosphorus should not be infused any faster than 10 mEq/hr.

role of the respiratory system

Role of the Respiratory System In relation to acid-base balance, the lungs are responsible for one of two functions: either retaining more carbon dioxide (CO2) to increase the acidity of the blood or removing excess CO2 from the blood to decrease the acidity of the blood. To retain CO2, the lungs slow the rate of respiration, allowing more CO2 to remain in the blood where it can work to increase acidity. To remove excess CO2, the lungs increase the rate of respiration so that they can exhale the excess CO2 from the body into the atmosphere. The decrease in the blood level of CO2 serves to also decrease the acidity. This relatively simple respiratory mechanism helps to maintain the balance between acids and bases, keeping the pH within the normal range between 7.35 and 7.45. These chemical changes occur very quickly but can correct a limited variance in pH, plus the correction is somewhat short lived. To further explain the relationship of CO2 to the level of acidity of the blood, let's see how CO2 becomes an acid. When the lungs are unable to exhale all of the CO2 that body cells create during metabolism, excess CO2 molecules remaining in the blood form ionic bonds with molecules of water (H2O). Each ionic bond of CO2 and H2O results in formation of carbonic acid (H2CO3). Carbonic acid is a weak acid that can only increase the acidity of the blood by releasing free hydrogen (H+) ions. As you have already learned, excess H+ ions increase the acidity of the blood and drop the pH so that the acids and bases are no longer balanced. The above chemical reaction is demonstrated here: CO2 + H2O → H2CO3 → H+ + HCO3- (carbon dioxide + water → carbonic acid → hydrogen bicarbonate)

acid base balance

cid-Base Balance All components of the human body function together with the intent of maintaining homeostasis, a state of balance essential to maintain basic cellular functions and sustain life. One area of homeostasis that must be maintained is the acid-base balance of body fluids. An acid is a substance that can donate a hydrogen ion (H+), and by doing so helps to increase the hydrogen concentration of a solution, making it more acidic. A base or alkaline substance is one that can accept an H+ ion or donate a hydroxyl ion (OH-), both of which help to decrease the concentration of hydrogen ions and increase alkalinity. Acid-base balance refers to the balance of the acids and alkaline bases of body fluids. A prolonged or extreme imbalance between the two will lead to death. pH Scale The status of acid-base balance is determined by comparing the number of acidic free hydrogen ions (H+) to the number of alkaline hydroxyl ions (OH-) present in body fluids. The OH- is simply one oxygen and one hydrogen that have bonded together. Because the H+ is no longer a free ion of hydrogen but is bonded with the oxygen ion, it is no longer an acid. A solution that is acidic contains a higher concentration of hydrogen ions than hydroxyl ions. If a solution has an equal concentration of the two ions, the solution is neutral. When the hydrogen ion concentration is less than that of the hydroxyl ions, the solution is alkaline. The scale that is used to determine this acid-base balance is known as the pH scale; pH stands for parts hydrogen. The scale ranges from 0 to 14, with a pH between 0 and 6.9 being acidic, and 0 being the most acidic; 7 is neutral; and 7.1 to 14 is alkaline or base, with 14 being the most alkaline. If you look at Figure 29-6, it is easy to see that a pH below the neutral 7 has more hydrogen ions than hydroxyl ions, making it acidic. On the other end of the scale, you can discern that a pH above neutral 7 contains more hydroxyl ions than hydrogen ions, making the solution alkaline. Safety: An individual's blood pH must stay within a very narrow range that is slightly alkaline to ensure survival: between 7.35 and 7.45. Other body fluids each have a different pH (see Fig. 29-6). Knowledge Connection What do the "p" and the "H" in pH stand for? What is the normal range of pH of human blood? Explain how the pH scale works, including what happens to both components involved in pH measurement. Figure 29-6 The pH scale. Compare the H+ ion concentration to the OH- ion concentration between 0 and 1 for the most acidic pH. Then compare the H+ ion and OH- ion concentrations between 13 and 14 for the most alkaline pH. The neutral pH of 7 shows an equal concentration of H+ ions and OH- ions. Note the pH of various common household items indicated along the bottom edge. Then compare their pH to the pH of different body fluids indicated across the top edge. (From Scanlon V, Sanders T. Essentials of Anatomy and Physiology. 7th ed. Philadelphia: FA Davis; 2015.) Regulation of Acid-Base Balance Three basic systems work together in the body to regulate and maintain acid-base balance. Each system does its part to compensate for alterations in pH caused when one of the three systems becomes impaired and is unable to perform its normal functions to maintain acid-base balance. The three systems are the: 1. Bicarbonate buffer system 2. Respiratory system—the lungs control retention and elimination of carbon dioxide (CO2), an acid 3. Renal system—the kidneys control retention and elimination of hydrogen (H), an acid, and sodium bicarbonate (NaHCO3), a base Note: Sodium bicarbonate (NaHCO3) is commonly used interchangeably with bicarbonate (HCO3-) when discussing blood gases, as you will notice in this chapter. It is important to note that other metabolic processes and diseases, besides diseases of the kidneys, also can impair acid-base balance. Bicarbonate Buffer System A buffer is a substance that can bind, or form an ionic bond, with a strong acid or base to prevent large changes in the pH of body fluids. Another way to look at it is that a buffer binds with a strong acid to decrease acidity, or the buffer binds with a strong base to decrease alkalinity of the body. The bicarbonate buffer system consists of the following two chemicals that help to prevent the extreme changes in pH that cause increased acidity and increased alkalinity: 1. Sodium bicarbonate (NaHCO3): a weak base 2. Carbonic acid (H2CO3): a weak acid To maintain acid-base balance, the following ratio must be met: 1 part H2CO3 to 20 parts NaHCO3. (Box 29-6 presents an explanation of the chemical symbols for sodium bicarbonate and carbonic acid.) Both sodium bicarbonate and carbonic acid have the ability to react with another substance to create either a weaker acid or a base. Box 29-6 Symbol Similarity As you may have already noticed, there is some similarity between the chemical symbol for the weak base sodium bicarbonate (NaHCO3) and the symbol for the weak acid carbonic acid (H2CO3). Let's look at the sodium bicarbonate symbol and break it down: Na and HCO3. You probably already know that the Na represents sodium. The remaining HCO3 represents bicarbonate. Here is where you may have noticed the similarity. The symbol for carbonic acid, H2CO3, is the same as the symbol for bicarbonate, HCO3, except that it has a "2" after the hydrogen symbol. This means that the carbonic acid has two hydrogen atoms, noted as H2, while bicarbonate has only one hydrogen atom, noted as H. Otherwise, both symbols have the same one carbon atom, noted as C, and three oxygen atoms, noted as O3. Buffer and Strong Acid Produce Weaker Acid When sodium bicarbonate, a weak base, combines with a strong acid (such as hydrochloric acid, HCl) in an attempt to reduce the acidity caused by the strong acid, it yields two chemicals that cannot maintain the previous higher level of acidity. These two chemicals are sodium chloride and a much weaker acid you are familiar with: carbonic acid. In other words, the weak base combines with a strong acid to make a weaker acid. NaHCO3 + HCl → NaCl + H2CO3 (Sodium bicarbonate, a weak base + hydrochloric acid, a strong acid → harmless sodium chloride + carbonic acid, a weak acid) Buffer and Strong Base Produce Weaker Base When carbonic acid, a weak acid, combines with a strong base (such as sodium hydroxide, NaOH) in an attempt to reduce the alkalinity caused by the strong base, it yields two chemicals that cannot maintain the previous higher level of alkalinity. These two chemicals are water and a weaker base you are familiar with: sodium bicarbonate. H2CO3 + NaOH → H2O + NaHCO3 (carbonic acid, a weak acid + sodium hydroxide, a strong base → water + sodium bicarbonate, a weaker base) Knowledge Connection What is the chemical symbol for sodium bicarbonate? For hydrogen? For hydrochloric acid? What is the ratio of carbonic acid to sodium bicarbonate that must be maintained to keep acid-base balance?