Positive end expiratory pressure ventilation, renal function and renin.

Positive end expiratory pressure (PEEP) during respirator therapy can impair renal function by altering renal haemodynamics or by increasing the secretion of the antidiuretic hormone. In the present study, the effect of the commonly used 10 cm H2O PEEP for two hours on renal function and on plasma renin activity was studied in eleven intensive care patients. During the examination period, the patients received analgesic, sedative, and muscle relaxant drugs, but no diuretics. PEEP decreased the mean urinary output by 21%. Urinary specific gravity and osmolality increased. Urinary sodium excretion decreased along with urinary volume. The creatinine clearance decreased slightly, but free water clearance became less negative suggesting reduced ability of tubules to concentrate urine during PEEP. The plasma renin activity was not altered significnalty by PEEP, nor did the urinary sodium/potassium ratio change. This may indicate that the water retention induced by PEEP is not caused by the increased secretion of aldosterone. The results suggest that 10 cm H2O PEEP impairs renal function in critically ill patients and causes mainly water retention.