Fluids, Electrolytes, and Acid–Base Status

Quick Look Test

Patients with minor fluid shifts may be asymptomatic, but patients who are severely fluid overloaded may present with pulmonary edema causing tachypnea and hypoxia. Patients with hypoxia will be quite agitated and distressed.

Airway and Vital Signs

The first step in evaluating fluid status is to check the vital signs. Tachypnea may be present in settings of pulmonary edema. If you suspect pulmonary edema, check the oxygenation of the patient with pulse oximetry.

Tachycardia also may be present in fluid overload as the heart attempts to unload the fluid accumulation in the lungs.

Selective History and Chart Review

• Check the input and output measurements (I/Os) for the past day or so. Do not forget the output from drains and tubes.

• These measurements are notoriously inaccurate but may supply clues. Another clue is the daily weight.

• Has the patient had aggressive fluid resuscitation?

• Does the patient have a disease that would predispose to fluid sequestration?

• How are the renal function and the liver function?

• Is the patient taking medication or therapy that might alter fluid distribution?

• Is the patient improving?

• After a serious illness or major surgery a patient may sequester several liters of fluid by third spacing. This will return to the vascular space during the recovery phase and may cause transient fluid overload.

• Is the patient worsening, or is there a change in fluid status, indicating MI or systemic infection?

Selective Physical Examination

Evaluation of neck veins is often a reasonable assessment of central venous pressure (CVP). When the patient is evaluated while lying down, note the fullness of the external jugular vein. Then slowly raise the head of the bed until the neck veins lose their fullness and pulsations are noted. Note the distance between the point of pulsation and the approximate position of the right atrium on a vertical axis (measure to the sternal notch and add 5 cm; Fig. 12.2 ). The distance is a gross estimate of the CVP in centimeters of water.

A measurement of 2 to 3 cm above the sternal notch is normal in adults. Patients with fluid overload may have jugular venous distention (JVD) at greater than 3 cm; lesser than 2 cm or consistently flat neck veins despite lying flat indicates fluid depletion.

Additional tests:

• 1.

  UA: Low specific gravity supports fluid overload if the kidneys are functioning normally.

• 2.

  Electrolytes: To assess for metabolic derangement and elevations in blood urea nitrogen (BUN) and creatinine (Cr).

• 3.

  Urine Na ⁺ : Assessment of renal function (see Table 33.2 ).

Initial Management

• 1.

  Support oxygenation as necessary.

• 2.

  Order intravenous (IV) access if not already available.

Definitive Management

• 1.

  Correct the underlying cause if known.

• 2.

  Limit ongoing fluid replacement regimens.

• 3.

  If the patient is in respiratory distress, maintain oxygenation and monitor with pulse oximetry. Consider intubation if necessary. Notify your resident.

• 4.

  Consider diuretic therapy as outlined in Chapter 33 .

• 5.

  Rarely, if diuretic therapy is ineffective, hemodialysis may be required.

Quick Look Test

Patients with minor fluid shifts (<10%) may be asymptomatic. Greater losses are associated with stupor and drowsiness. Major fluid deficit can cause hypotension and shock (see Chapter 17 ).

Airway and Vital Signs

The first step in evaluating fluid status is to check the vital signs. Orthostatic vital signs are the most useful in determining a deficiency in intravascular volume. Orthostatics are heart rate (HR) and BP taken while the patient is lying flat, while the patient is sitting, and while the patient is standing. Allow a minute or two to pass between each change in position so the patient may equilibrate. A rise in HR of 15 beats/minute or a drop in systolic BP (SBP) of 15 mm Hg or any drop in diastolic BP with a change in position is evidence of a significant intravascular deficit and may require fluid replacement. Also be mindful of any symptoms that the patient exhibits during changes in position. Dizziness on standing may also indicate loss of intravascular volume. In a young individual, BP is tightly controlled and may be maintained easily with only an increase in pulse rate despite dangerous hypovolemia. In these patients, tachycardia with a stable BP may be the last step before complete cardiovascular collapse. Also, β-blockade may mask increases in HR and result in profound drops in BP on changes in position.

Tachycardia itself is not sufficient to make the diagnosis of intravascular depletion, as it may also be present in fluid overload states.

Selective History and Chart Review

Check the I/Os for the past day or so. This measurement is notoriously inaccurate but may supply clues. Remember that UO is an indication of renal perfusion. Look carefully at the most recent changes in UO. Check the daily weights.

Has the patient had inadequate maintenance fluid replacement?

Does the patient have a disease that would predispose to fluid loss?

How is the renal function? (See Chapter 33 . )

Is the patient taking medication or therapy that might alter fluid distribution?

Is the patient worsening, or is there a change in fluid status, indicating sepsis or another form of shock?

Selective Physical Examination

Initial Management

• 1.

  Support perfusion and oxygenation as necessary.

• 2.

  Order orthostatics if not already done.

• 3.

  Order IV access if not already available, or better yet, place them yourself.

Definitive Management

• 1.

  Correct the underlying cause if known (see Table 12.2 for a list of common etiologies).

• 2.

  Choose an appropriate fluid to replace the loss. If fluid behind, a bolus of 500 to 1000 cc and readdressing can usually correct the derangement faster than adjusting the maintenance rate.

• 3.

  Replace fluids with the goal of maintaining adequate end-organ perfusion.

• 4.

  Choose a rate of rehydration that the patient can tolerate and reevaluate frequently with examinations of respiratory rate (RR), lung fields for rales, skin for adequate perfusion, and I/Os for consistent UO.

Red Blood Cells

If the fluid deficit is a result of ongoing blood loss, the correct fluid to replace is generally packed red blood cells (RBCs). Whole blood, which replaces plasma volume and RBCs, may not be available at all hospitals but may be reconstructed by the blood bank from packed RBCs and fresh frozen plasma (FFP). Always check with the resident before replacing blood or blood products.

Blood Products

These include FFP, cryoprecipitate, albumin, and platelets. They are used as a colloid source of volume expansion and also may replace or fulfill specific deficiencies such as specific blood coagulation factors or thrombocytopenia. Many now argue that if the patient is bleeding, the volume should be replaced with equal parts RBC, FFP, and platelets to help correct hypovolemia and hypocoagulable states.

Colloid

These include albumin, dextran 40 or 70, and hetastarch. The goal of colloid administration is to replace fluid and osmotic elements to the intravascular space. Theoretically, colloids serve to draw fluid from the interstitium by exerting osmotic pressure. They carry lower risks for infection than blood products and are more rapidly available. Some colloids are used to enhance microcirculation by reducing blood viscosity, which may be desirable after revascularization procedures. Albumin is often used to augment resuscitation, particularly in specific populations such as those who have undergone cardiac bypass or liver failure/hepatic resections. However, many of these colloid products have fallen out of routine clinical practice because of recent high-quality clinical trials and meta-analyses demonstrating lack of superiority of colloids in resuscitation for critically ill patients. In some groups, mortality and other negative endpoints were higher in those receiving colloids. The use of hetastarch now carries a black box warning by the FDA and are no longer used. Dextran resuscitation has fallen out of use.

Crystalloid

Crystalloid is the most widely used option because it is available and inexpensive. Even if another fluid is ultimately desirable, it is often worth beginning the volume expansion with crystalloid until the other product becomes available. Because of its easy passage from the intravascular space into the extravascular space, crystalloid replacement tends to take four times the volume to achieve the same expansion of the intravascular space as does colloid. A list of available crystalloid products and their electrolyte compositions are presented in Table 12.4 .