NMS. Surgery

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Part I ♦ Foundations B. Hypernatremia (Na + > 150 mEq/L) 1. Categories a. Hypovolemia: Hypernatremia represents a free water deficit; total body sodium may be low. b. Hypervolemia: Iatrogenic infusion of too much sodium can lead to hypervolemic hypernatremia, but this is rare. 2. Signs and symptoms: Similar to volume depletion (e.g., tachycardia, hypotension, dry mucous membranes, decreased skin turgor); water shifts from the intracellular compartment can produce neurological signs and symptoms (lethargy, confusion, and coma). 3. Diagnosis/etiology (usually simple): High serum sodium with obvious free water losses. a. Extrarenal losses: Insensible losses due to fever, mechanical ventilation, burns, diarrhea, or measured losses from the GI tract. b. Renal losses: Excessive free water excretion. (1) Osmotic diuresis from hyperglycemia or mannitol administration. (2) High-output dilute urine from acute tubular necrosis (ATN). 4. Treatment a. Hypovolemia: Need to replace volume; calculate free water deficit first: (1) Water deficit = 0.6 × body weight (kg) × (serum Na+/140−1). (2) Replace half the deficit in the first 8 hours; the rest in the next 16 hours. (3) If the hypovolemic state is severe (i.e., shock), then initial resuscitation can be isotonic fluids. If the deficit is less severe, use dextrose 5% in water (D5W) to complete the free water replacement. b. Hypervolemia (1) If total body water is increased, then decrease the amount of sodium administered. (2) If sodium intake (e.g., antibiotics, total parenteral nutrition [TPN]) cannot be decreased, free water can be infused to lower the serum sodium level. (3) Diuretics can be used, but sodium can rise. (4) Consider natriuresis. III. Potassium A. Hypokalemia (K + <3.5 mEq/L): Severe hypokalemia is a serum potassium level of 3.0 mEq/L or less; in some patients (e.g., cardiac), a K + higher than 4.0 is desirable. 1. Signs and symptoms: Ileus, weakness, and cardiac dysrhythmias.

Electrocardiogram (ECG) changes may occur below a K + of 3.0 mEq/L and include, in increasing order of severity, T-wave flattening or inversion, depressed ST segments, development of U waves, prolonged QT interval, and ventricular tachycardia.