One hour and 15 minutes into the procedure, the patient’s serum Na+ level is 102 mEq/L. How would one correct the Na+ level to 135 mEq/L?
The sodium deficit must first be calculated using the following equation:
Na+deficit mEq = total body water (TBW) × (Na+desired − Na+observed)
TBW comprises 60% of lean body weight in the average male and 50% of lean body weight in the average female. In this example, the patient’s sodium deficit is:
1,425.6 mEq = (72 kg × 0.6) × (135 − 102)
Hypertonic saline (3% NaCl) contains 513 mEq/L of Na+. Therefore, the volume of hypertonic saline required to replace a Na+ deficit of 1,425.6 mEq is 2.78 liters. The maximum safe rate of rise in a patient’s serum sodium is 0.5 mEq/L/hr. In this case, the serum Na+ should be corrected over 66 hours. Therefore, the hypertonic saline should run at a rate of 1,425.6/66 = 21.6 cc/hr.
In situations of significant hyponatremia associated with seizures and/or progressive neurologic deterioration, it may be necessary to correct the Na+ deficit more rapidly (up to 3 mEq/L/hr). This rapid correction should not exceed 2 hours and should be stopped if the neurologic symptoms resolve sooner.