Atrial natriuretic factor may mediate the renal effects of PEEP ventilation.

Mechanical ventilation with PEEP decreases urine output and urinary sodium excretion. Observed changes in cardiac output, renal blood flow, renin release, and antidiuretic hormone (ADH) secretion do not adequately explain the renal effects of PEEP. Altered release of atrial natriuretic factor (ANF), which is natriuretic and diuretic, may complete this explanation. The following hypothesis was tested: a PEEP-induced decrease in transmural right atrial pressure decreases ANF release, and this mechanism mediates subsequent alterations in renal function. Seven female mongrel dogs were anesthetized with halothane and their lungs ventilated mechanically for three consecutive 40 min periods of 0 PEEP, 10 cmH2O PEEP, and 0 PEEP. Addition of 10 cmH2O PEEP during mechanical ventilation decreased right atrial dimension and transmural right atrial pressure while intracavitary right atrial pressure was increased. Urine output was significantly decreased during PEEP, as were absolute and fractional excretion of sodium and osmolar clearance. PEEP ventilation resulted in a consistent and significant decline in plasma ANF concentration (82 +/- 11 to 62 +/- 11 pg/ml, P less than 0.05). Hemodynamic parameters, renal function, and ANF concentration returned to control values after cessation of PEEP. A second series of experiments in five dogs demonstrated a close temporal relationship between changes in atrial dimension or atrial transmural pressure, plasma ANF concentration, and urine output or sodium excretion. The results of this study demonstrate that PEEP-induced decreases in atrial distension resulted in decreased ANF release, which may mediate, in part, the antinatriuretic and antidiuretic effects of PEEP.