The mechanism of water and sodium retention during positive end-expiratory pressure (PEEP) ventilation

To investigate the mechanism of water and sodium retention during PEEP ventilation, ten dogs were studied at 0, 1.33Kpa, 2.67Kpa PEEP and at spontaneous breathing. Hemodynamics, renal excretory function parameters and plasma hormonal parameters were recorded at the end of each period. Compared with spontaneous breathing, PEEP induced a significant reduction of diuresis (from 31.8 +/- 17.9 to 11.2 +/- 6.4ml/h, P < 0.01) and natriuresis (from 5.21 +/- 4.93 to 1.09 +/- 1.22 mmol/h, P < 0.01), whereas plasma atrial natriuresis factor (ANF) fell from 1219 +/- 446 to 713 +/- 344 pg/ml (P < 0.05) and esophageal pressure increased from 0.13 +/- 0.42 to 1.22 +/- 0.66Kpa (P < 0.01), serum aldosterone (ALD) increased from 295 +/- 281 to 1012 +/- 685 pg/ml (P < 0.05). There was a significant correlation between ANF and ALD (r = -0.647, P < 0.001). We suggest that changes in ANF in response to intrathoracic pressure may contribute to alteration of renal excretory function during PEEP.