Chapter 41: Fluid, Electrolyte, and Acid-Base Balance

A nursing student is teaching a healthy adult client about adequate hydration. Which statement by the client indicates understanding of adequate hydration?

"I should drink 2,500 mL/day of fluid." Explanation: In healthy adults, fluid intake generally averages approximately 2,500 mL/day, but it can range from 1,800 to 3,000 mL/day with a similar volume of fluid loss.

A client admitted to the facility is diagnosed with metabolic alkalosis based on arterial blood gas values. When obtaining the client's history, which statement would the nurse interpret as a possible underlying cause?

"I've been taking antacids almost every 2 hours over the past several days." Explanation: Metabolic alkalosis occurs when there is excessive loss of body acids or with unusual intake of alkaline substances. It can also occur in conjunction with an ECF deficit or potassium deficit (known as contraction alkalosis). Vomiting or vigorous nasogastric suction frequently causes metabolic alkalosis. Endocrine disorders and ingestion of large amounts of antacids are other causes. Hyperventilation, commonly caused by anxiety or pain, would lead to respiratory alkalosis. Fever, which increases carbon dioxide excretion, would also be associated with respiratory alkalosis. Severe diarrhea is associated with metabolic acidosis.

The nurse is caring for a client who will be undergoing surgery in several weeks. The client states, "I would like to give my own blood to be used in case I need it during surgery." What is the appropriate nursing response?

"Let me refer you to the blood bank so they can provide you with information." Explanation: Referring the client to a blood bank is the appropriate response. Most blood given to clients comes from public donors. In some cases, when a person anticipates the potential need for blood in the near future or when procedures are used to reclaim blood from wound drainage, the client's own blood may be reinfused.

A client has been diagnosed with a gastrointestinal bleed and the health care provider has ordered a transfusion. At what rate should the nurse administer the client's packed red blood cells?

1 unit over 2 to 3 hours, no longer than 4 hours Explanation: Packed red blood cells are administered 1 unit over 2 to 3 hours for no longer than 4 hours.

A healthy client eats a regular, balanced diet and drinks 3,000 mL of liquids during a 24-hour period. In evaluating this client's urine output for the same 24-hour period, the nurse realizes that it should total approximately how many mL?

3,000 Explanation: Fluid intake and fluid output should be approximately the same in order to maintain fluid balance. Any other amount could lead to a fluid volume excess or deficit.

A health care provider orders an infusion of 250 mL of NS in 100 minutes. The set is 20 gtt/ml What is the flow rate?

50 gtt/min Explanation: The flow rate (gtt/min) equals the volume (mL) times the drop factor (gtt/mL) divided by the time in minutes.

A health care provider orders a bolus infusion of 250 mL of normal saline to run over 1 hour. The set delivers 20 gtt/mL. What is the flow rate in gtt/min?

83 gtt/min Explanation: The flow rate (gtt/min) equals the volume (mL) times the drop factor (gtt/mL) divided by the time in minutes. 250 mL × 20 gtt/mL ÷ 60 min = 83 gtt/min

The nurse is calculating an infusion rate for the following order: Infuse 1,000 mL of 0.9% NaCl over 12 hours using an electronic infusion device. What is the infusion rate?

83 mL/hr Explanation: When calculating the infusion rate with an electronic device, divide the total volume to be infused (1,000 mL) by the total amount of time in hours (12). This is 83 mL/hr. Other options are incorrect.

A client with a diagnosis of colon cancer has opted for a treatment plan that will include several rounds of chemotherapy. What vascular access device is most likely to meet this client's needs?

An implanted central venous access device (CVAD) Explanation: Implanted CVADs are ideal for long-term uses such as chemotherapy. The short-term nature of peripheral IVs, and the fact that they are sited in small-diameter vessels, makes them inappropriate for the administration of chemotherapy. Because of the caustic nature of most chemotherapy agents, peripheral IV's are not appropriate.

What is the lab test commonly used in the assessment and treatment of acid-base balance?

Arterial blood gas Explanation: ABGs are used to assess acid-base balance. The pH of plasma indicates balance or impending acidosis or alkalosis. The complete blood cell count measures the components of the blood, focusing on the red and white blood cells. The urinalysis assesses the components of the urine. Basic metabolic panel (BMP) assess kidney function (BUN and creatinine), sodium and potassium levels, and blood glucose level.

A nurse is caring for a client who requires intravenous (IV) therapy. The nurse understands that which actions are the nurse's responsibilities related to this therapy? Select all that apply.

Deciding the location of the IV catheter. Deciding the size of the IV catheter. Administering the IV solution. Explanation: The nurse is responsible for deciding the location and size of the IV catheter, as well as for administering the solution. The primary care provider is responsible for prescribing the kind and amount of solution.

The nursing is caring for a client who has a peripheral intravenous (IV) catheter in place. The nurse is flushing the new IV tubing to hang the infusion. After reviewing the actions performed by the nurse in the image, which step should the nurse take next?

Discard the tubing, prime new tubing and administer the infusion at the prescribed rate of flow Explanation: Intravenous site solutions should not become contaminated at any point prior to or during the priming process or when preparing to administer or connect an IV catheter to a client's IV site. The other answers are incorrect and not appropriate.

A nurse inspecting a client's IV site notices redness and swelling at the site. What would be the most appropriate nursing intervention for this situation?

Discontinue the IV and relocate it to another site. Explanation: The nurse should inspect the IV site for the presence of phlebitis (inflammation), infection, or infiltration and discontinue and relocate the IV if any of these signs are noted. Cleansing will not resolve this common complication of therapy.

A nurse is inspecting the IV site of a client and notices that the site is swollen, red, warm to the touch, and painful. Which action by the nurse is appropriate?

Discontinue the IV and relocate it to another spot. Explanation: The nurse should inspect the IV site for presence of phlebitis (inflammation), infection, or infiltration and discontinue and relocate the IV if any of these signs are noted. Cleaning with alcohol or chlorhexidine is not recommended and does not reduce the phlebitis. The nurse does not need to call the health care provider for anti-inflammatory medications.

The nurse is caring for a client with "hyperkalemia related to decreased renal excretion secondary to potassium-conserving diuretic therapy." What is an appropriate expected outcome?

ECG will show no cardiac arrythmias within 48 hours after removing salt substitutes, coffee, tea, and other K+-rich foods from diet. Explanation: If the client is taking a potassium-conserving diuretic, he must be mindful of the amount of potassium he is ingesting because the potassium level is more likely to elevate above normal. Cardiac arrythmias may result if hyperkalemia occurs. Supplemental potassium should not be added to the client's intake. Potassium does not have a direct impact on bowel motility.

A nurse is required to initiate IV therapy for a client. Which should the nurse consider before starting the IV?

Ensure that the prescribed solution the expected color and consistency. Explanation: Before preparing the solution, the nurse should inspect the container and determine that the solution's color and consistency matches that expected based on the prescription, the expiration date has not elapsed, no leaks are apparent, and a separate label is attached. The primary tubing should be approximately 110 inches (2.8 m) long and the secondary tubing should be about 37 inches (94 cm) long. To reduce the potential for infection, IV solutions are replaced every 24 hours even if the total volume has not been completely instilled.

The nurse has inserted a peripheral intravenous catheter. When applying a transparent dressing, what is the nurse's best action?

Explanation: The transparent dressing should be placed in such a manner as to allow full coverage and visibility of the insertion site, without excessively covering the tubing.

A nurse is changing a client's peripheral venous access dressing. The nurse finds that the site is bleeding and oozing. Which type of dressing should the nurse use for this client?

Gauze dressing Explanation: A gauze dressing is recommended if the client is diaphoretic or if the site is bleeding or oozing. However, the gauze dressing should be replaced with a transparent semipermeable membrane once this is resolved. Transparent semipermeable membranes are a type of sealed IV dressing. Occlusive dressings would not be appropriate.

A nurse is obtaining an arterial blood specimen from a client to assess acid-base status. Which value is expected for a client with normal status?

HCO3: 25 mEq/L (25 mmol/L) Explanation: Normal values include: HCO3: 22 to 26 mEq/L; pH: 7.35 to 7.45; PaCO2: 35; and SaO2: oxygen saturation greater than 95%.

A nurse is providing care to a client with hypocalcemia. The nurse would monitor the client's laboratory test results for which imbalance?

Hyperphosphatemia Explanation: Calcium and phosphorus have a reciprocal relationship—if the calcium level is low, the phosphorus level would be high. A magnesium deficiency, not excess, may be accompanied by hypocalcemia. Sodium and potassium deficiencies are not typically associated with low calcium levels.

When providing chemotherapeutic agents, which catheter is accessed with a non-coring needle?

Implanted venous access catheter Explanation: Implanted venous access catheters are accessed with a non-coring needle such as a Huber point needle.

An older adult client with hypokalemia is being discharged to the home of a caregiver. Which information should the nurse include in the family teaching?

Include more bananas in the diet. Explanation: Hypokalemia is a below-normal potassium level. Bananas are high in potassium. Adding bananas to the diet can help increase the serum potassium level. Canned vegetables, cheese, and bread do not have a high potassium content.

A nurse is caring for a client who has recently suffered burns on 30% of his body. Based on his condition, what type of IV solution might be ordered for this client?

Lactated Ringer's Explanation: Lactated Ringer's solution is a roughly isotonic solution that contains multiple electrolytes in about the same concentrations as found in plasma (note that this solution is lacking in Mg2+ and PO43- ). It is used in the treatment of hypovolemia, burns, and fluid lost as bile or diarrhea and in treating mild metabolic acidosis.

A client is admitted to the unit with a diagnosis of intractable vomiting for 3 days. What acid-base imbalance related to the loss of stomach acid does the nurse observe on the arterial blood gas (ABG)?

Metabolic alkalosis Explanation: Metabolic alkalosis is associated with an excess of HCO3, a decrease in H+ ions, or both, in the extracellular fluid (ECF). This may be the result of excessive acid losses or increased base ingestion or retention. Loss of stomach acid may result in this condition. Metabolic acidosis is a proportionate deficit of bicarbonate in ECF. The deficit can occur as the result of an increase in acid components or an excessive loss of bicarbonate such as in diarrhea. Respiratory acidosis is when the carbon dioxide level is high and the ph is low. Respiratory alkalosis is when the carbon dioxide level is low and the ph is high.

As observed the nurse changing a peripheral venous access site dressing is demonstrating inappropriate technique by implementing which action?

Not wearing gloves when performing the intervention Explanation: The changing of a peripheral venous access site dressing requires the use of clean gloves to minimize the transmission of microorganisms during the procedure and to prevent the nurse from coming into contact with blood. The intervention does not require sterile precautions. The manner in which the nurse is applying stabilizing pressure to the catheter and pulling the adhered dressing toward the insertion site demonstrates appropriate technique.

The nurse is administering intravenous (IV) therapy to a client. The nurse notices acute tenderness, redness, warmth, and slight edema of the vein above the insertion site. Which complication related to IV therapy should the nurse most suspect?

Phlebitis Explanation: Phlebitis is an inflammation of a vein caused by mechanical trauma from a needle or catheter. It is characterized by local acute tenderness, redness, warmth, and slight edema of the vein above the insertion site. Infiltration, the escape of fluid into the subcutaneous tissue, is caused by a dislodged needle or penetrated vessel wall. It is characterized by swelling, pallor, coldness, or pain around the infusion site and a significant decrease in the flow rate. Sepsis, or infection, is caused by invasion of microorganisms. It is characterized by erythema, edema, induration, drainage at the insertion site, fever, malaise, chills, and other vital sign changes. Air embolism is air in the circulatory system caused by a break in the IV system above the heart level. It is characterized by respiratory distress, increased heart rate, cyanosis, decreased blood pressure, and a change in level of consciousness.

A 50-year-old client with hypertension is being treated with a diuretic. The client reports muscle weakness and falls easily. The nurse should assess which electrolyte?

Potassium Explanation: Diuretics, commonly given to treat high blood pressure and heart failure, can cause an extracellular deficit or loss of electrolytes including potassium, calcium, and magnesium. Signs of potassium defecit, or hypokalemia, include muscle weakness and leg cramps, fatigue, paresthesias, and arrythmias.

The nurse is responding to a client's call light. The client states, "I was getting out of bed and caught my IV on the side rail. I think I may have pulled it out." The nurse determines that the intravenous (IV) catheter has been almost completely pulled out of the insertion site. Which is the appropriate action for the nurse?

Remove the IV catheter and reinsert another in a different location. Explanation: An IV catheter should not be reinserted. Whether the IV is salvageable depends on how much of the catheter remains in the vein. Because this catheter has been almost completely pulled out of the insertion site, it should be discarded and a new one inserted at a different location. It is not acceptable simply to apply a new dressing and leave the catheter sticking out of the site.

The nurse is caring for a client receiving intravenous fluids through a peripheral intravenous catheter (IV). On rounds, the nurse notes that the client's IV site and arm are swollen and cool to the touch. Based on these assessment findings, what will the nurse do next?

Remove the peripheral intravenous catheter. Explanation: The assessment findings of a swollen IV site with surrounding tissue swelling and cool to touch indicate infiltration. The correct action for an infiltrated IV is to remove the IV. Decreasing the rate of fluids requires the health care provider's prescription and is not indicated for infiltration. Placing a warm compress is not indicated for infiltration. Elevating the swollen extremity is for peripheral edema, not infiltration.

When caring for a client who is on intravenous therapy, the nurse observes that the client has developed redness, warmth, and discomfort along the vein. Which intervention should the nurse perform for this complication?

Restart infusion in another vein and apply a warm compress. Explanation: Prolonged use of the same vein can cause phlebitis; the nurse should apply a warm compress after restarting the IV. The nurse need not elevate the client's head, position the client on the left side, or apply antiseptic and a dressing. The client's head is elevated if the client exhibits symptoms of circulatory overload. The client is positioned on the left side if exhibiting signs of air embolism. The nurse applies antiseptic and a dressing to an IV site in the event of an infection.

A client is diagnosed with hypovolemia after significant blood loss. Which action will the nurse take?

Start an IV of normal saline as prescribed. Explanation: To treat a client with hypovolemia, the nurse should obtain an IV bag with normal saline (0.9% sodium chloride) as prescribed. Fluid intake by mouth will not provide fluid quickly enough for the desired effect but should be attempted if feasible, in addition to an IV. Orange juice with additional sugar may be given to a person with low blood sugar.

A nurse is administering a blood transfusion to a client. After 15 minutes, the client reports difficulty breathing. What is the first action by the nurse?

Stop the transfusion and infuse normal saline using a new administration set. Explanation: A client who reports difficulty breathing during a blood transfusion may be having a transfusion reaction. The first action is to stop the transfusion and infuse normal saline using a new administration set. Changing the administration set prevents the client from receiving more of the blood that is causing the reaction. After stopping the transfusion and infusing normal saline using a new administration set, the nurse should check the client's vital signs and notify the health care provider of the reaction.

During a blood transfusion of a client, the nurse observes the appearance of rash and flushing in the client, although the vital signs are stable. Which intervention should the nurse perform for this client first?

Stop the transfusion immediately. Explanation: The nurse needs to stop the transfusion immediately. The nurse should prepare to give an antihistamine because these signs and symptoms are indicative of an allergic reaction to the transfusion, infuse saline at a rapid rate, and administer oxygen if the client shows signs of incompatibility.

The nurse is preparing a packed red blood cell transfusion for a client. The nurse checks the client's blood type in the electronic medical record (EMR) and notes that it is blood type B. What does this mean?

The client has anti-A antibodies. Explanation: Clients with type B blood have anti-A antibodies. This means they would attack any type A blood they receive, prompting a transfusion reaction. Clients with type O blood are universal donors.

The nurse is assessing a client's intravenous line and notes small air bubbles within the tubing. What is the priority nursing action?

Tighten the roller clamp to stop the infusion. Explanation: The priority nursing action is to tighten the roller clamp on the tubing as this action prevents forward movement of air. All other options are appropriate to remove the air once the tubing has been clamped.

The nurse is preparing to administer fluid replacement to a client. Which action should the nurse take first?

Verify the prescription for type of solution and amount of infusion. Explanation: The nurse should verify the prescription from the health care provider first. The prescription for intravenous therapy should include the type of solution, the volume, possible additives, and the duration of the infusion. After verifying the prescription, the nurse prepares the solution for administration, performs a venipuncture, and regulates the rate of administration.

The oncoming nurse is assigned to the following clients. Which client should the nurse assess first?

a newly admitted 88-year-old with a 2-day history of vomiting and loose stools Explanation: Young children, older adults, and people who are ill are especially at risk for hypovolemia. Fluid volume deficit can rapidly result in a weight loss of 5% in adults and 10% in infants. A 5% weight loss is considered a pronounced fluid deficit; an 8% loss or more is considered severe. A 15% weight loss caused by fluid deficiency usually is life threatening. It is important to ambulate after surgery, but this can be addressed after assessment of the 88-year-old. The stable MI client presents no emergent needs at the present. The pain is important to address and should be addressed next or simultaneously (asking a colleague to give pain med).

An infant is brought to the emergency room with dehydration due to vomiting. After several failed attempts to start an IV, the nurse observes a scalp vein. When accessing the scalp vein, the nurse should use:

a winged infusion needle. Explanation: Winged infusion needles are short, beveled needles with plastic flaps or wings. They may be used for short-term therapy or when therapy is given to a child or infant.

The nurse writes a a problem-based care plan, citing the client's excess fluid volume. What risk factor does the nurse expect to assess in this client?

acute kidney injury Explanation: Excess fluid volume may result from increased fluid intake or from decreased excretion, such as occurs with progressive acute kidney failure. Excessive use of laxatives, diaphoresis, and increased cardiac output may lead to a fluid volume deficit.

Which client is at a greater risk for fluid volume deficit related to the loss of total body fluid and extracellular fluid?

an infant age 4 months Explanation: An infant has considerably more total body fluid and extracellular fluid (ECF) than does an adult. Because ECF is more easily lost from the body than intracellular fluid, infants are more prone to fluid volume deficits. An adolescent at 17 years is considered to have an adultlike body system similar to the 45-and 50-year-old.

A nurse is reviewing the dietary intake of a client prescribed a potassium-sparing diuretic. The client tells the nurse that they had a banana, yogurt, and bran cereal for breakfast and a turkey sandwich with a glass of milk for lunch. The intake of which food would be a cause for concern?

banana Explanation: Bananas are high in potassium and would place the client receiving a potassium-sparing diuretic at risk for increased potassium levels. Milk and yogurt are good sources of calcium and phosphorus and would not be a concern. Turkey provides protein and would not be problematic.

The nurse is caring for a client who had a parathyroidectomy. Upon evaluation of the client's laboratory studies, the nurse would expect to see imbalances in which electrolytes related to the removal of the parathyroid gland?

calcium and phosphorus Explanation: The parathyroid gland secretes parathyroid hormone, which regulates the level of calcium and phosphorus. Removal of the parathyroid gland will cause calcium and phosphorus imbalances. Sodium, chloride, and potassium are regulated by the kidneys and affected by fluid balance.

The nurse is educating a client with hypokalemia on why it is important to maintain potassium balance. Which does the nurse include in the teaching?

cardiac function Explanation: Potassium is essential for normal cardiac function. Optic, auditory, and skeletal function are dependent to other electrolytes.

A client's most recent blood work indicates a K+ level of 7.2 mEq/L (7.2 mmol/L), a finding that constitutes hyperkalemia. For what signs and symptoms should the nurse vigilantly monitor?

cardiac irregularities Explanation: Hyperkalemia compromises the normal functioning of the sodium-potassium pump and action potentials. The most serious consequence of this alteration in homeostasis is the risk for potentially fatal cardiac arrythmias. Muscle weakness is associated with low magnesium or high phosphorus. Increased intracranial pressure is a result of increase of blood or brain swelling. Metabolic acidosis is associated with a low pH, a normal carbon dioxide level and a low bicarbonate level.

Which is a common anion?

chloride Explanation: Chloride is a common anion, which is a negatively charged ion. Magnesium, potassium, and calcium are cations, or positively charged ions.

A client who is NPO prior to surgery reports feeling thirsty. What is the physiologic process that drives the thirst factor?

decreased blood volume and intracellular dehydration Explanation: Located within the hypothalamus, the thirst control center is stimulated by intracellular dehydration and decreased blood volume. When a client does not drink, the body begins intracellular dehydration and the client becomes thirsty. There is no extracellular dehydration.

A nurse who has diagnosed a client as having "fluid volume excess" related to compromised regulatory mechanism (kidneys) may have been alerted by what symptom?

distended neck veins Explanation: Fluid volume excess causes the heart and lungs to work harder, leading to the veins in the neck becoming distended. Muscle twitching, and nausea and vomiting may signify electrolyte imbalances. The sternum is not an area assessed during fluid volume excess.

A nurse is reviewing the client's serum electrolyte levels which are as follows: Sodium: 138 mEq/L (138 mmol/L)Potassium: 3.2 mEq/L (3.2 mmol/L)Calcium: 10.0 mg/dL (2.5 mmol/L)Magnesium: 2.0 mEq/L (1.0 mmol/L)Chloride: 100 mEq/L (100 mmol/L)Phosphate: 4.5 mg/dL (2.6 mEq/L) Based on these levels, the nurse would identify which imbalance?

hypokalemia Explanation: All of the levels listed are within normal ranges except for potassium, which is decreased (normal range is 3.5 to 5.3 mEq/L; 3.5 to 5.3 mmol/L). Therefore, the client has hypokalemia.

A client age 80 years, who takes diuretics for management of hypertension, informs the nurse that she takes laxatives daily to promote bowel movements. The nurse assesses the client for possible symptoms of:

hypokalemia. Explanation: The frequent use of laxatives and diuretics promotes the excretion of potassium and magnesium from the body, increasing the risk for fluid and electrolyte deficits.

During an assessment of an older adult client, the nurse notes an increase in pulse and respiration rates, and notes that the client has warm skin. The nurse also notes a decrease in the client's blood pressure. Which medical diagnosis may be responsible?

hypovolemia Explanation: The nurse should recognize that hypovolemia, also known as dehydration, may be responsible. Additional indicators of dehydration in older adults include mental status changes; increases in pulse and respiration rates; decrease in blood pressure; dark, concentrated urine with a high specific gravity; dry mucous membranes; warm skin; furrowed tongue; low urine output; hardened stools; and elevated hematocrit, hemoglobin, serum sodium, and blood urea nitrogen (BUN). Hypervolemia means a higher-than-normal volume of water in the intravascular fluid compartment and is another example of a fluid imbalance that would manifest itself with different signs and symptoms. Edema develops when excess fluid is distributed to the interstitial space.

Which solution is a crystalloid solution that has the same osmotic pressure as that found within the cells of the body and is used to expand the intravascular volume?

isotonic Explanation: Isotonic fluids have an osmolarity of 250-375 mOsm/L, which is the same osmotic pressure as that found within the cell.

Mr. Jones is admitted to the nurse's unit from the emergency department with a diagnosis of hypocalcemia. His laboratory results show a serum calcium level of 8.2 mg/dL (2.05 mmol/L). For what assessment findings will the nurse be looking?

muscle cramping and tetany Explanation: Manifestations of hypocalcemia include numbness and tingling of fingers, mouth, or feet; tetany; muscle cramps; and seizures. Manifestations of hypercalcemia include nausea, vomiting, constipation, bone pain, excessive urination, thirst, confusion, lethargy, and slurred speech. Diminished cognitive ability and hypertension may result from hyperchloremia. Constipation is a sign of hypercalcemia.

A client is admitted to the nursing unit from the emergency department with a diagnosis of hypokalemia. Laboratory results show a serum potassium of 3.2 mEq/l (3.2 mmol/l). For what set of manifestations should the nurse be alert?

muscle weakness, fatigue, and arrythmias Explanation: Typical signs of hypokalemia include muscle weakness and leg cramps, fatigue, paresthesias, and arrythmias. Manifestations of hypercalcemia include nausea, vomiting, constipation, bone pain, excessive urination, thirst, confusion, lethargy, and slurred speech. Diminished cognitive ability and hypertension may result from hyperchloremia. Constipation is a sign of hypercalcemia.

A student nurse is selecting a venipuncture site for an adult client. Which action by the student would cause the nurse to intervene?

placing the tourniquet on the upper arm for 2 minutes Explanation: The tourniquet should not be applied for longer than 1 minute, as this allows for stasis of blood that can lead to clotting and also creates prolonged discomfort for the client. Other options are correct techniques when preparing for venipuncture.

A decrease in arterial blood pressure will result in the release of:

renin. Explanation: Decreased arterial blood pressure, decreased renal blood flow, increased sympathetic nerve activity, and/or low-salt diet can stimulate renin release.

An intravenous hypertonic solution containing dextrose, proteins, vitamins, and minerals is known as:

total parenteral nutrition. Explanation: Total parenteral nutrition is a hypertonic solution containing 20% to 50% dextrose, proteins, vitamins, and minerals that is administered into the venous system.