NMS. Surgery

7

Chapter 1 ♦ Principles of Surgical Physiology

Hyponatremia

Hypo-osmotic

Normo-osmotic

Hyperosmotic

Hypovolemic

Euvolemic

Hypervolemic

Figure 1-2: Hyponatremia.

2. Signs and Symptoms a. Acute hyponatremia: Acute cerebral edema, seizures, and coma. b. Chronic hyponatremia: Tolerated to Na + concentrations of 110 mEq/L; signs and symptoms include confusion, irritability, and decreased deep tendon reflexes. 3. Diagnosis and categorization: Clinical exam and lab determination of osmolar state are often enough for diagnosis; when in doubt, check urine osmolarity and sodium. a. Hypovolemic, hypo-osmolar hyponatremia: Urine Na + greater than 20 mEq/L = renal losses; urine Na + less than 10 mEq/L = extrarenal losses. b. Hypervolemic, hypo-osmolar hyponatremia: Urine Na + greater than 20 mEq/L = renal failure; Na + less than 10 mEq/L = cirrhosis, heart failure. c. Euvolemic, hypo-osmolar hyponatremia: Urine osmolarity usually high; urine Na + usually greater than 20 mEq/L except in water intoxication. 4. Treatment (if minimally symptomatic) a. Hyperosmolar: Correct hyperglycemia or other active osmotic particles. b. Normo-osmolar: Treat the underlying disease process. c. Hypo-osmolar (1) Hypovolemic: Treat with isotonic fluid infusion to restore deficits. (2) Hypervolemic: Treat underlying medical cause first, and then initiate salt and free water restrictions. (3) Euvolemic: If SIADH, free water restriction usually is sufficient.