Inappropriate response to increased plasma ADH during mechanical ventilation in acute respiratory failure

Abstract

The effect of mechanical prolonged ventilation (IPPV) and positive end expiratory pressure (PEEP) on plasma ADH was studied in eight patients with acute respiratory failure. The study was divided into two 60 min periods, PEEP of 10 cm H2O being added to IPPV during first or second hour in random order. Mean decreases in urinary flow from 1.11 to 0.78 ml/min (P<0.05) and cardiac index (determined in six patients) from 4.3 to 3.4 l/min/m2 (P<0.01) were observed with PEEP. Although a twofold increase in plasma ADH (mean 8.1 to 18.8 μU/ml, P<0.05) following PEEP was associated with a decrease in urinary flow, inconsistent changes in free water and osmolal clearance and urinary osmolality point to an inappropriate response to increased ADH. The decrease in urinary flow and concurrent reduction in urinary sodium excretion suggest an overriding influence of the decrease in cardiac index on renal function.