Fluids Balance: Thirst

Perhaps the simplest mechanism for maintaining fluid balance is the thirst mechanism. Thirst occurs as a result of even small losses of fluid. Losing body fluids or eating highly salty foods leads to an increase in ECF osmolality. This increase leads to the drying of mucous membranes in the mouth, which in turn stimulates the thirst center in the hypothalamus.

Fluid Balance: Quenching that thirst

Usually, when a person is thirsty, he drinks fluid. The ingested fluid is absorbed from the intestine into the bloodstream, where it moves freely between fluid compartments. This movement leads to an increase in the amount of fluid in the body and a decrease in the concentration of solutes, thus balancing fluid levels throughout the body.

Fluid Balance: Fluid and electrolyte imbalances

Fluid and electrolyte balance is essential for health. Many factors, such as illness, injury, surgery, and treatments, can disrupt a patient’s fluid and electrolyte balance. Even a patient with a minor illness is at risk for fluid and electrolyte imbalance. (See Understanding electrolyte imbalances.)

Fluid Balance: Dehydration

The body loses water all the time. A person responds to the thirst reflex by drinking fluids and eating foods that contain water. However, if water isn’t adequately replaced, the body’s cells can lose water. This causes dehydration, or fluid volume deficit. Dehydration refers to a fluid loss of 1% or more of body weight.

Signs and symptoms of dehydration include:

  • dizziness
  • fatigue
  • weakness
  • irritability
  • delirium
  • extreme thirst
  • dry skin and mucous membranes
  • poor skin turgor
  • increased heart rate
  • falling blood pressure
  • decreased urine output
  • seizures and coma (in severe dehydration).

Laboratory values may include a serum sodium level above 150 mEq/L and serum osmolality above 305 mOsm/kg. The patient may also have an increase in his blood urea nitrogen and hemoglobin levels.

Treatment of dehydration involves determining its cause (such as diarrhea or decreased fluid intake) and replacing lost fluids — either orally or I.V. Most patients receive hypotonic, lowsodium fluids such as dextrose 5% in water (D5W).

Fluid Balance: Hypervolemia

Hypervolemia refers to an excess of isotonic fluid (water and sodium) in ECF. The body has compensatory mechanisms to deal with hypervolemia. However, if these fail, signs and symptoms develop.

Hypervolemia can occur if a person consumes more fluid than needed, if fluid output is impaired, or if too much sodium is retained. Conditions that may lead to hypervolemia include kidney failure, cirrhosis, heart failure, and steroid therapy.

Depending on the severity of hypervolemia, signs and symptoms may include:

  • edema
  • weight gain

Understanding electrolyte imbalances

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  • distended neck and hand veins
  • heart failure
  • initially, rising blood pressure and cardiac output; later, falling values.

Laboratory tests may reveal a serum sodium level above 135 mEq/L and serum osmolality below 275 mOsm/kg.

Treatment involves determining the cause and treating the underlying condition. Typically, patients require fluid and sodium restrictions and diuretic therapy.

Fluid Balance: Water intoxication

Water intoxication occurs when excess fluid moves from the ECF to the ICF. Excessive low-sodium fluid in the ECF is hypotonic to cells; cells are hypertonic to the fluid. As a result, fluids shift into the cells, which have comparatively less fluid and more solutes. The fluid shift, in turn, balances the concentrations of fluid between the two spaces.

Fluid Balance: Acting inappropriately

Water intoxication may occur in a patient with syndrome of inappropriate antidiuretic hormone, which can result from central nervous system or pulmonary disorders, head trauma, tumors, or the use of certain drugs. Other causes of water intoxication include:

  • rapid infusion of hypotonic solutions
  • excessive use of tap water as a nasogastric tube irrigant or e nema
  • psychogenic polydipsia, a psychological disturbance in which a person drinks large amounts of fluid even when they aren’t needed.

Fluid Balance: I.V. fluid replacement

To maintain health, the balance of fluids and electrolytes in the intracellular and extracellular spaces must remain relatively constant. Whenever a person experiences an illness or a condition that prevents normal fluid intake or causes excessive fluid loss, I.V. fluid replacement may be necessary.

Fluid Balance: Quick and predictable

I.V. therapy that provides the patient with life-sustaining fluids, electrolytes, and medications offers the advantages of immediate and predictable therapeutic effects. The I.V. route is, therefore, the preferred route — especially for administering fluids, electrolytes, and drugs in an emergency.

This route also allows for fluid intake when a patient has GI malabsorption. I.V. therapy permits accurate dosage titration for analgesics and other medications. Potential disadvantages associated with I.V. therapy include drug and solution incompatibility, adverse reactions, infection, and other complications.

Fluid Balance: Types of solutions

Solutions used for I.V. fluid replacement fall into the broad categories of crystalloids (which may be isotonic, hypotonic, or hypertonic) and colloids (which are always hypertonic).


Crystalloids are solutions with small molecules that flow easily from the bloodstream into cells and tissues. Isotonic crystalloids contain about the same concentration of osmotically active particles as ECF, so fluid doesn’t shift between the extracellular and intracellular areas.

Hypotonic crystalloids are less concentrated than ECF, so they move from the bloodstream into the cell, causing the cell to swell. In contrast, hypertonic crystalloids are more highly concentrated than ECF, so fluid is pulled into the bloodstream from the cell, causing the cell to shrink. (See Comparing fluid tonicity.)

Isotonic solutions

Isotonic solutions, such as D5W, have an osmolality (or concentration) of 275 to 295 mOsm/kg. The dextrose metabolizes quickly, however, acting like a hypotonic solution and leaving water behind. Large amounts of the solution may cause hyperglycemia.

Comparing fluid tonicity

Fluid Balance

Fluid Balance: Did someone ring for more isotonic solutions?

Normal saline solution, another isotonic solution, contains only the electrolytes sodium and chloride. Other isotonic fluids are more similar to ECF. For instance, Ringer’s solution contains sodium, potassium, calcium, and chloride. Lactated Ringer’s solution contains those electrolytes plus lactate, which the liver converts to bicarbonate.


Hypotonic fluids

Hypotonic fluids are those fluids that have an osmolality less than 275 mOsm/kg. Examples of hypotonic fluids include:

  • half-normal saline solution
  • 0.33% sodium chloride solution
  • dextrose 2.5% in water.

Fluid Balance: It makes a cell swell

Hypotonic solutions should be given cautiously because fluid then moves from the extracellular space into cells, causing them to swell. That fluid shift can cause cardiovascular collapse from vascular fluid depletion. It can also cause increased intracranial pressure (ICP) from fluid shifting into brain cells.

Hypotonic solutions shouldn’t be given to a patient at risk for increased ICP — for example, those who have had a stroke, head trauma, or neurosurgery. Signs of increased ICP include a change in the patient’s level of consciousness, motor or sensory deficits, and changes in the size, shape, or response to light in the pupils. Hypotonic solutions also shouldn’t be used for patients who suffer from abnormal fluid shifts into the interstitial space or the body cavities — for example, as a result of liver disease, a burn, or trauma.

Hypertonic solutions

Hypertonic solutions are those that have an osmolality greater than 295 mOsm/kg. Examples include:

  • dextrose 5% in half-normal saline solution
  • dextrose 5% in normal saline solution
  • dextrose 5% in lactated Ringer’s solution
  • dextrose 10% in water.

Fluid Balance: The incredible shrinking cell

A hypertonic solution draws fluids from the intracellular space, causing cells to shrink and the extracellular space to expand. Patients with cardiac or renal disease may be unable to tolerate extra fluid. Watch for fluid overload and pulmonary edema.

Because hypertonic solutions draw fluids from cells, patients at risk for cellular dehydration (patients with diabetic ketoacidosis, for example) shouldn’t receive them.


The practitioner may prescribe a colloid (plasma expander) if your patient’s blood volume doesn’t improve with crystalloids. Examples of colloids that may be given include:

  • albumin (available in 5% solutions, which are osmotically equal to plasma, and 25% solutions, which draw about four times their volume in interstitial fluid into the circulation within 15 minutes of administration)
  • plasma protein fraction
  • dextran
  • hetastarch.

Fluid Balance: Flowing into the stream

Colloids pull fluid into the bloodstream. The effects of colloids last several days if the lining of the capillaries is normal. The patient needs to be closely monitored during a colloid infusion for increased blood pressure, dyspnea, and bounding pulse, which are all signs of hypervolemia.

If neither crystalloids nor colloids are effective in treating the imbalance, the patient may require a blood transfusion or other treatment.

Fluid Balance: Delivery methods

The choice of I.V. therapy delivery is based on the purpose of the therapy and its duration; the patient’s diagnosis, age, and health history; and the condition of the patient’s veins. I.V. solutions can be delivered through a peripheral or a central vein. Catheters are chosen based on the therapy and the site to be used. Here’s a look at how to choose a site — peripheral or central — and which equipment you’ll need for each.

Peripheral lines

Peripheral I.V. therapy is administered for short-term or intermittent therapy through a vein in the arm, hand, leg or, rarely, foot. Potential I.V. sites include the metacarpal, cephalic, basilic, median cubital, and greater saphenous veins. Using veins in the leg or foot is unusual because of the risk of thrombophlebitis. Also keep in mind that dextrose concentrations greater than 10% shouldn’t be administered peripherally because of the risk of vein irritation.

Central lines

Central venous therapy involves administering solutions through a catheter placed in a central vein, typically the subclavian or internal jugular vein, less commonly the femoral vein.

Central venous therapy is used for patients who:

  • have inadequate peripheral veins
  • need access for blood sampling
  • require a large volume of fluid
  • need a hypertonic solution to be diluted by rapid blood flow in a larger vein
  • need to receive vessel-irritating drugs
  • need a high-calorie nutritional supplement.

Types of central venous catheters include the traditional multilumen catheter for short-term therapy and a peripherally inserted central catheter or a vascular access device (such as a Broviac or Hickman catheter) for long-term therapy.

Fluid Balance: Complications of I.V. therapy

Caring for a patient with an I.V. line requires careful monitoring as well as a clear understanding of the possible complications, what to do if they arise, and how to deal with flow issues.


During infiltration, fluid may leak from the vein into surrounding tissue. This occurs when the access device dislodges from the vein. Look for coolness at the site, pain, swelling, leaking, and lack of blood return. Also look for a sluggish flow that continues even if a tourniquet is applied above the site. If you see infiltration, stop the infusion, elevate the extremity, and apply warm soaks.

Fluid Balance: Smaller is better

To prevent infiltration, use the smallest catheter that will accomplish the infusion, avoid placement in joint areas, and secure the catheter in place.


I.V. therapy involves puncturing the skin, one of the body’s barriers to infection. Look for purulent drainage at the site, tenderness, erythema, warmth, or hardness on palpation. Signs and symptoms that the infection has become systemic include fever, chills, and an elevated white blood cell count.

Fluid Balance: This monitoring is vital

Nursing actions for an infected I.V. site include monitoring vital signs and notifying the practitioner. Swab the site for culture and remove the catheter as ordered. Always maintain sterile technique to prevent this complication.

Phlebitis and thrombophlebitis

Phlebitis is inflammation of a vein. Thrombophlebitis is an irritation of the vein along with the formation of a clot; it’s usually more painful than phlebitis. Poor insertion technique or the pH or osmolality of the infusing solution or medication can cause these complications. Look for pain, redness, swelling, or induration at the site; a red line streaking along the vein; fever; or a sluggish flow of the solution.


Fluid Balance: Prevention begins with big veins

When phlebitis or thrombophlebitis occurs, remove the I.V. line, monitor the patient’s vital signs, notify the practitioner, and apply warm soaks to the site. To prevent these complications, choose large veins and change the catheter according to your facility’s policy when infusing a medication or solution with high osmolality.


Extravasation, similar to infiltration, is the leakage of fluid into surrounding tissues. It results when medications, such as dopamine, calcium solutions, and chemotherapeutic agents, seep through veins and can produce blistering and necrosis. Initially, the patient may experience discomfort, burning, or pain at the site. Also, look for skin tightness, blanching, and lack of blood return. Delayed reactions include inflammation and pain within 3 to 5 days and ulcers or tissue necrosis within 2 weeks.

Fluid Balance: Review policy

When administering medications that may extravasate, know your facility’s policy. Nursing actions include stopping the infusion, notifying the practitioner, removing the catheter, applying ice early and warm soaks later, and elevating the extremity. The doctor may inject an antidote into the site. Assess the circulation and nerve function of the limb.

Air embolism

An air embolism occurs when air enters the vein. It can cause a decrease in blood pressure, an increase in the pulse rate, respiratory distress, an increase in ICP, and a loss of consciousness.

Fluid Balance: Problems in the air

If the patient develops an air embolism, notify the practitioner and clamp off the I.V. line. Place the patient on his left side and lower his head to allow the air to enter the right atrium, where it can disperse more safely by way of the pulmonary artery. Monitor the patient and administer oxygen. To avoid this serious complication, prime all tubing completely, tighten all connections securely, and use an air detection device on an I.V. pump.

How you intervene

Nursing care for the patient with an I.V. line includes the following actions:

  • Check the I.V. order for completeness and accuracy. Most I.V. orders expire after 24 hours. A complete order should specify the amount and type of solution, specific additives and their concentrations, and the rate and duration of the infusion. If the order is incomplete or confusing, clarify the order with the prescriber before proceeding.
  • Measure intake and output carefully at scheduled intervals. The kidneys attempt to restore fluid balance during dehydration by reducing urine production. Urine output less than 30 ml/hour signals retention of metabolic wastes. Notify the practitioner if your patient’s urine output falls below 30 ml/hour.
  • Monitor daily weights to document fluid retention or loss. A 2% increase or decrease in body weight is significant. A 2.2-lb (1-kg) change corresponds to 1 qt (1 L) of fluid gained or lost.
  • Always carefully monitor the infusion of solutions that contain medication because rapid infusion and circulation of the drug can be dangerous.
  • Note the pH of the I.V. solution. The pH can alter the effect and stability of drugs mixed in the I.V. bag. Consult medication literature, the pharmacist, or the prescriber if you have questions.
  • Using sterile technique, change the site, dressing, and tubing as often as facility policy requires. Solutions should be changed at least every 24 hours.
  • When changing I.V. tubing, be sure not to move or dislodge the I.V. catheter. If you have trouble disconnecting the used tubing, use a hemostat to hold the I.V. hub while twisting the tubing. Don’t clamp the hemostat shut because doing so may crack the hub.
  • Always report needle-stick injuries immediately so that treatment can be initiated. Exposure to a patient’s blood increases the risk of infection with blood-borne viruses, such as human immunodeficiency virus (HIV), hepatitis B virus, hepatitis C virus, and cyto megalovirus. About 1 out of 300 people with occupational needle-stick injuries become HIV-seropositive.
  • Always follow standard precautions when inserting, caring for, or discontinuing an I.V. line.

Fluid Balance: Focus on the patient

Focus Topic: Fluids and electrolytes

  • Always listen to your patient carefully. Subtle statements such as “I just don’t feel right” may be your clue to the beginning of an allergic reaction.
  • Provide appropriate patient teaching. (See Teaching about I.V. therapy.)
  • Keep in mind that a candidate for home I.V. therapy must have a family member or friend who can safely and competently administer the I.V. fluids as well as a backup helper, a suitable home environment, a telephone, available transportation, adequate reading skills, and the ability to prepare, handle, store, and dispose of equipment properly. Procedures for caring for the I.V. line are the same at home as in a health care facility, except at home the patient uses clean technique instead of sterile technique.

Teaching about I.V. therapy

Fluid Balance