Influence of rehydration on organ blood flow after hypernatremic shock in the unrestrained young minipig.

Hypernatremic shock was produced in the minipig by feeding hyperosmolar solutions, which led to osmotic diuresis and dehydration. Weight loss was 14%, serum values (in mmol/L) were, for Na, 168; urea, 12.1; bicarbonate, 10.5; and pH 7.25 (mean values). Cardiac output was reduced by 51%, arterial pressure was unchanged (-5.1%); organ blood flow, measured with radioactive microspheres, was as follows: heart, -56%; brain, -35%; gastrointestinal tract, -60%; and kidneys, -57%. Intravenous rehydration for 24 h normalized weight, serum electrolytes, and pH; but had little effect on cardiac output and organ blood flow. Even prolongation of fluid therapy to 48 h did not restore the circulatory changes, which showed an arterial pressure of +4.3%; cardiac output, -31%; and flow to heart, -21%; brain, -24%; gastrointestinal tract, -30%; and kidneys, -47%. This pattern of diminished cardiac output, normal arterial pressure, and reduced organ blood flow not only in the splanchnic organs but also in heart and brain is similar to the hemodynamic response to vasopressin. Increased vasopressin release probably plays an important role after rehydration in hypernatremic shock.