Ch. 17 Fluid and electrolyte imbalance

Oncotic pressure

(colloidal osmotic pressure) is osmotic pressure exerted by colloids in solution. The major colloid in the vascular system contributing to the total osmotic pressure is protein.

Define the following process involved in the regulation of movement of water and electrolytes between the body fluid compartments:diffusion, osmosis, filtration, hydrostatic pressue, onctoic pressure, and osmotic pressure.

Diffusion is the movement of molecules from an area of high concentration to one of low concentration. Facilitated diffusion involves the use of a protein carrier in the cell membrane (and requires no energy). Osmosis is the movement of water from areas of low solute concentration to those of higher concentration.

Describe the etiology, lab and diagnostic findings, clinical manifestations, and nursing and collab management of different electrolytes imbalances

Fluid and electrolyte imbalances are classified as either deficits or excesses. Fluid volume deficit can occur with abnormal loss of body fluids (e.g., diarrhea, drainage, hemorrhage, and polyuria), inadequate intake, or a plasma-to-interstitial fluid shift. Fluid volume excess may result from excessive intake of fluids, abnormal retention of fluids (e.g., heart failure, renal failure), or interstitial-to-plasma fluid shift. The goals of treatment in fluid imbalances are to correct the underlying cause and to restore fluid and electrolyte balance.

Describe the composition and indications of common intravenous fluid solutions.

Fluid replacement therapy is used to correct many fluid and electrolyte imbalances. The amount and type of solution used is determined by patient requirements and laboratory results. Hypotonic solutions, such as 5% dextrose in water and 0.45% NaCl, provide more water than electrolytes, diluting the ECF and producing movement of water from the ECF to the ICF. Administration of an isotonic solution, such as lactated Ringer's and 0.9% NaCl, expands only the ECF. There is no net loss or gain from the ICF. A hypertonic solution initially increases the osmolality of the ECF and results in expansion of the ECF. It is used in the treatment of hypovolemia and hyponatremia. KCl, CaCl, MgSO4, and HCO3- are common additives to the basic IV solutions. Plasma expanders stay in the vascular space and increase the osmotic pressure.

Osmotic pressure

Is the strength of the osmotic pull based on the concentration of a solution (the higher the concentration, the greater the solution's pulling). In other words, is the amount of pressure required to stop the osmotic flow of water. Measuring osmolality is important because it indicates the water balance of the body.

Hyper-, and hypomagnesemia

Magnesium plays an important role in many essential cellular processes. Hypermagnesemia is an elevated serum magnesium level. It usually occurs when a patient with renal insufficiency or failure has an increased magnesium intake. Initial clinical manifestations include lethargy, drowsiness, and nausea and vomiting. With rising levels, deep tendon reflexes are lost, followed by somnolence, then respiratory and cardiac arrest. Primary treatment focuses on prevention by avoiding magnesium-containing medications and foods. Severe symptoms require treatment with IV calcium. Hypomagnesemia, a low serum magnesium level, is associated with malnutrition states, such as fasting or starvation. It produces neuromuscular and CNS hyperirritability. Clinical manifestations are related to neuromuscular and CNS irritability and include hyperactive deep tendon reflexes, tremors, seizures, and confusion. Treatment involves replacing magnesium.

Hyper, and hypophasphatemia

Phosphorus is a primary anion in the ICF and is essential to the function of muscle, red blood cells, and the nervous system. Hyperphosphatemia is an elevated serum phosphorus level. It is usually associated with acute or chronic renal failure. Symptoms include neuromuscular irritability, tetany, and calcified deposits in soft tissues. The primary management is treating the underlying cause. Hypophosphatemia is a low serum phosphorus level. It most often occurs in a patient who is malnourished or has a malabsorption syndrome. It is often asymptomatic. If symptoms occur, they are typically severe, requiring treatment with oral or IV phosphorus.

Hyper- and hypokalemia

Potassium is the major ICF cation and is the major factor in the resting membrane potential of nerve and muscle cells. Changes in potassium balance cause a number of clinical problems. Hyperkalemia is an elevated serum potassium level. The most common cause is renal failure. Hyperkalemia is also common with massive cell destruction (e.g., burn or crush injury, tumor lysis); rapid transfusion of stored, hemolyzed blood; and catabolic states (e.g., severe infections). The most clinically significant manifestations of hyperkalemia are disturbances in cardiac conduction. Other manifestations include cramping leg pain, followed by weakness or paralysis of skeletal muscles. Monitor the electrocardiograph of all patients with hyperkalemia to detect potentially fatal dysrhythmias and monitor the effects of therapy. The patient experiencing dangerous cardiac dysrhythmias should receive IV calcium gluconate. Hypokalemia is a low serum potassium level. The most common causes are from abnormal losses from either the kidneys or the gastrointestinal tract. Hypokalemia can cause potentially lethal ventricular dysrhythmias. Skeletal muscle weakness and paralysis, including the respiratory muscles, leading to shallow respirations and respiratory arrest, can occur. Patients taking digoxin experience increased digoxin toxicity if their serum potassium level is low. Treat hypokalemia by giving potassium chloride supplements and increasing dietary intake of potassium.

Hyper-, hyponatremia

Sodium is the major ECF cation and plays a major role in maintaining the concentration and volume of the ECF. Hypernatremia is an elevated serum sodium that may occur with water loss or sodium gain. Symptoms include those of dehydration and any accompanying ECF volume deficit, such as postural hypotension, weakness, and decreased skin turgor. Hypernatremia is treated by cause. With water deficits, volume is replaced. If sodium excess occurs, dilution is accomplished with sodium-free IV fluids. Hyponatremia is a low serum sodium level. Common causes include water excess from inappropriate use of sodium-free or hypotonic IV fluids. Symptoms of hyponatremia are related to cellular swelling and are primarily manifested in the central nervous system. In hyponatremia from water excess, fluid restriction is often the only treatment. If fluid loss is the cause, replacement with sodium-containing solutions is indicated.

Hyper, and hypo-calcemia

The functions of calcium include transmission of nerve impulses, myocardial contractions, blood clotting, formation of teeth and bone, and muscle contractions. Calcium is present in the serum in three forms: free or ionized; bound to protein (primarily albumin); and bound with phosphate, citrate, or carbonate. The ionized form is the biologically active form. Hypercalcemia is an elevated serum calcium level. Hyperparathyroidism causes two thirds of the cases. The remainder are caused by malignancy, especially from myeloma, breast, renal, or lung cancers. Manifestations include decreased memory, confusion, disorientation, fatigue, muscle weakness, constipation, cardiac dysrhythmias, and renal calculi. Treatment consists of promoting the excretion of calcium in urine by administering a loop diuretic and hydrating the patient with isotonic saline infusions. Hypocalcemia is a low serum calcium level. The most common cause is a decrease in the production of parathyroid hormone. Hypocalcemia causes increased muscle excitability resulting in tetany. Observe a patient who has had neck surgery, particularly a thyroidectomy, for signs of hypocalcemia. Treatment of hypocalcemia is usually oral or IV calcium supplementation.

Describe the compositon of the major body fluid compartments.

The two fluid compartments in the body are the intracellular space (inside the cells) and the extracellular space (outside the cells). Approximately two thirds of the body water is located within cells and is termed intracellular fluid (ICF). ICf is about 40% body weight of an adult. ECF consists of interstitial fluid (the fluid in the spaces between cells), plasma (the liquid part of blood), and transcellular fluid (a very small amount of fluid contained within specialized cavities of the body). In ECF the main cation is sodium, with small amounts of potassium, calcium, and magnesium. The primary ECF anion is chloride, with small amounts of bicarbonate, sulfate, and phosphate anions. In ICF the most prevalent cation is potassium, with small amounts of magnesium and sodium. The prevalent ICF anion is phosphate, with some protein and a small amount of bicarbonate.

Regulation of water balance

Water balance is maintained by water intake and excretion. An intact thirst mechanism is important for fluid balance. The patient who cannot recognize or act on the sensation of thirst is at risk for fluid deficit and hyperosmolality. An increase in plasma osmolality or a decrease in circulating blood volume stimulates antidiuretic hormone (ADH) secretion. Glucocorticoids and mineralocorticoids secreted by the adrenal cortex help regulate both water and electrolytes. Aldosterone, a mineralocorticoid, has potent sodium-retaining and potassium-excreting capability. The kidneys are the primary organs for regulating fluid and electrolyte balance. Kidneys regulate water balance through adjustments in urine volume. With severely impaired renal function, the kidneys cannot maintain fluid and electrolyte balance, resulting in edema and electrolyte imbalances. Insensible water loss, which is invisible vaporization from the lungs and skin, assists in regulating body temperature. The older adult experiences normal physiologic changes that increase his or her susceptibility to fluid and electrolyte imbalances. Functional changes may occur that affect the ability to obtain fluids independently.

Hydrostatic pressure

is the force within a fluid compartment and is the major force that pushes water out of the vascular system at the capillary level.