Page 436 - Clinical Application of Mechanical Ventilation

402 Chapter 12

Treatment of Extracellular Fluid Abnormalities

Treatment of ECF deficit is by fluid replacement with Ringer’s lactate solution since
it is similar to ECF in composition. Physiologic (0.9%) saline solution is an ac-
ceptable alternative. Success of fluid replacement therapy can be determined by
reversal of those signs of ECF deficit in Table 12-13. For example, decrease in heart
Decrease in heart rate, rate, increase in blood pressure and urine output are signs of improvement in ECF
increase in blood pressure
and urine output are signs of deficit after fluid replacement.
improvement in ECF deficit Excessive fluid in the extracellular space is uncommon in a clinical setting. When
after fluid replacement.
it occurs, pulmonary edema is a common manifestation. The treatment for excessive
ECF is to withhold fluid or to give a diuretic such as furosemide (Lasix). Mannitol
should not be given for diuresis as it can increase plasma volume before inducing
diuresis (Eggleston, 1985).
Use of diuretics will further increase the urine output. For this reason, reversal
of the cardiovascular signs of ECF excess in Table 12-13 should be used to deter-
Disappearance of mine the success of treatment. For example, disappearance of the pulmonic P heart
pulmonic P 2 heart sound, 2
reduction in pulse intensity, sound, reduction in pulse intensity, and clearing of pulmonary edema are signs of
and clearing of pulmonary improvement in ECF excess due to fluid restriction or diuresis. Since diuresis can af-
edema are signs of improve-
ment in ECF excess. fect the electrolyte composition, monitoring of electrolyte balance is essential when
diuretics are used to manage ECF excess.

ELECTROLYTE BALANCE

Electrolyte balance is the difference between the cations (positively charged ions)
and the anions (negatively charged ions) in the plasma. Serum cations and anions
are used to calculate the anion gap and assess a patient’s electrolyte balance.

Normal Electrolyte Balance

Table 12-14 shows the normal values for serum electrolytes. Sodium is the major
cation in the extracellular fluid compartment and it is directly related to the fluid
level in the body. Potassium is the major cation in the intracellular fluid compart-
ment and it is not related to the amount of fluid in the body.
Sodium and potassium are the two major electrolytes that must be monitored. In
general, once the sodium and potassium concentrations are properly managed and
returned to normal, the chloride concentration will be corrected as well without fur-
ther intervention. The following sections cover sodium and potassium abnormalities.

Anion Gap. Anion gap is the difference between the cations [sodium (Na ) and po-
1
anion gap: The difference 1 2 -
between cations (positive ions) tassium (K )] and the anions [chloride (Cl ) and bicarbonate (HCO )]. The normal
3
and anions (negative ions) in range is 15–20 mEq/L when K is included in the calculation (10–14 mEq/L when
1
the plasma. The normal range is
1
1
15–20 mEq/L when K is included K is excluded). When the anion gap is outside this range, electrolyte replacement
in the cal culation (10–14 mEq/L may be necessary. See Chapter 9 for a discussion on the interpretation of anion gap
1
when K is excluded).
in metabolic acidosis.

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