Profound natriuresis, extracellular fluid volume contraction, and hypernatremia with hypertonic losses following...

A young male sustained very serious head and soft tissue injuries in a motor vehicle accident (MVA). Three interesting problems developed in the sodium (Na) and water area in the second week in hospital. First, on day 11 after the MVA, his urine output increased to 3 liters per day; the urine osmolality was 1000 mOsm/kg H2O and Na and Cl were the principal urine osmoles. There appeared to be a salt wasting syndrome because he had a very large natriuresis (close to 900 mmol/24 hr) at a time when his central venous pressure was low. To help identify the nephron site responsible for a natriuresis with a high urine osmolality, additional studies were carried out in normal volunteers who took a loop or a thiazide diuretic on different occasions while ADH was acting. The pattern of natriuresis in the patient was similar to that after the thiazide but not the loop diuretic. The second problem concerned his hypernatremia (153 mM) because his urine was hypertonic and his intravenous therapy was isotonic saline. To explain hypernatremia while receiving more electrolyte-free water, we speculated that there was a water shift into cells resulting from particles generated and retained in his intracellular fluid. Given the large shift of water required, a lesion in muscle was suspected, a form of rhabdomyolysis. The third problem concerned the rate of catabolism of lean body mass. The metabolic consequences of generating these intracellular particles and the large amount of urea that was excreted could reflect a large degree of protein catabolism.