Positive end-expiratory pressure reduces renal excretion without hormonal activation after volume expansion in dogs

Abstract

Controlled mechanical ventilation (CMV) with positive end-expiratory airway pressure decreases urine output and renal sodium excretion. This study investigates-independent of surgical stress, general anesthesia, and sedation-the influences of antidiuretic hormone, atrial natriuretic peptide, plasma renin activity, and aldosterone on decreased urine output and renal sodium excretion during CMV with positive end-expiratory airway pressure. Hemodynamic, renal, and hormonal parameters were measured over a 4-h period in six trained, nonanesthetized, chronically tracheotomized dogs under two conditions: 1) control: hours 1-4, spontaneous breathing at continuous positive airway pressure of 4 cmH2O; and 2) CMV 20: hour 1, continuous positive airway pressure of 4 cmH2O; hours 2 and 3, CMV with a mean airway pressure of 20 cmH2O; and hour 4, continuous positive airway pressure of 4 cmH2O. Throughout the experiments, 0.5 ml · kg body weight-1 · min-1 balanced electrolyte solution was administered intravenously. During the 2nd and 3rd h of CMV 20, urine volume decreased by 43% and sodium excretion decreased by 44% when compared with control values (P < 0.05). The glomerular filtration rate decreased from 4.4 ± 0.1 to 3.9 ± 0.1 ml · kg-1 · min-1 (P < 0.05) during the 2nd h and from 4.4 ± 0.1 to 4.1 ± 0.1 ml · kg-1 · min-1 (P < 0.05) during the 3rd h of CMV 20. Fractional sodium excretion decreased from 4.7 ± 0.3% to 2.9 ± 0.2% (P < 0.05) during the 2nd h and from 7.5 ± 0.3% to 4.6 ± 0.2% (P < 0.05) during the 3rd h of CMV 20, compared with values during the control period. CMV 20 did not alter the mean arterial pressure and heart rate. Compared with control values, CMV 20 caused central venous pressure to increase during the 2nd h from 5 ± 0.2 to 8 ± 0.4 mmHg (P < 0.05) and during the 3rd h from 6 ± 0.2 to 9 ± 0.2 mmHg (P < 0.05). Release of antidiuretic hormone, atrial natriuretic peptide, and aldosterone was not affected by CMV 20. Plasma renin activity decreased during the course of the study from 0.9 ± 0.2 to 0.3 ± 0.1 ng angiotensin I · ml-1 · h-1 (P < 0.05) in both protocols, although plasma renin activity was higher in the 2nd h during CMV 20 than during the control period (1.3 ± 0.2 vs. 0.8 ± 0.1 ng angiotensin I · ml-1 · h-1; P < 0.05). This demonstrates that, in awake dogs in whom extracellular volume is expanded, antidiuretic hormone, atrial natriuretic peptide, and aldosterone do not participate in the urine- and sodium-retaining effect of short-term mechanical ventilation with positive end-expiratory airway pressure. However, plasma renin activity may well contribute to the water and sodium retention during CMV with positive end-expiratory airway pressure.