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

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 less than 0.05). The glomerular filtration rate decreased from 4.4 +/- 0.1 to 3.9 +/- 0.1 ml.kg-1.min-1 (P less than 0.05) during the 2nd h and from 4.4 +/- 0.1 to 4.1 +/- 0.1 ml.kg-1.min-1 (P less than 0.05) during the 3rd h of CMV 20. Fractional sodium excretion decreased from 4.7 +/- 0.3% to 2.9 +/- 0.2% (P less than 0.05) during the 2nd h and from 7.5 +/- 0.3% to 4.6 +/- 0.2% (P less than 0.05) during the 3rd h of CMV 20, compared with values during the control period.(ABSTRACT TRUNCATED AT 250 WORDS)