Effect of positive pressure breathing on plasma antidiuretic hormone and renal function in dogs

The effect of intermittent mechanical ventilation and positive end-expiratory pressure on plasma antidiuretic hormone concentration was determined in 14 pentobarbital anesthetized dogs. The study was divided into a control period (spontaneous respiration), and two consecutive 30 and 60 min periods after the start of controlled respiration: Group I - intermittent positive breathing (IPPB); Group II - positive end-expiratory pressure (PEEP) with 5 cm H2O. A decrease in urinary flow (36.9%) was observed during end-expiratory pressure breathing. An increase in plasma antidiuretic hormone in group II from 4.5 +/- 2.4 to 24.6 +/- 16.0 pg/ml (P less than 0.01) was associated with a significant reduction of free water clearance from 1.2 +/- 0.6 to 0.3 +/- 0.4 ml/min and an increase of the urine/plasma osmolality ratio (143%, P less than 0.05). The decrease in urinary output and concurrent reduction of urinary sodium excretion also suggest an influence of the fall in glomerular filtration rate and renal plasma flow on renal function. IPPB only reduced total Na+ and K+ excretion. These results indicate that the mechanisms underlying the renal response to positive end-expiratory pressure breathing may be due to an increase in antidiuretic hormone plasma levels leading to a fall in urinary flow and in part to a decrease in sodium excretion.