Acute changes in bladder volume produce minimal cardio-respiratory responses in lightly anesthetised humans

Abstract

Purpose: To examine whether changes in bladder volume elicit reflex cardiovascular and respiratory responses in humans under general anesthesia with sevoflurane and nitrous oxide. Methods: Fourteen patients free of autonomic disorders were anesthetized with sevoflurane 0.5% and nitrous oxide 60% in oxygen that were approximately equivalent to 0.9 MAC. Warmed saline (6 ml · kg-1, 37°C) was instilled into the pre-emptied urinary bladder, and then the bladder was kept distended for five minutes. Following the distension, the instilled saline was drained to the pre-instilled volume of the bladder. Arterial blood pressure, respiratory flow, and intra-vesicle pressure were continuously measured, and mean arterial pressure, pulse rate, respiratory rate, tidal volume, and minute ventilation were estimated offline from these signals. Results: Bladder emptying produced small decreases in mean blood pressure (from 83.4 ± 4.3 to 80.0 ± 4.4 mmHg, mean ± SE, P = 0.017) and pulse rate (from 72.2 ± 2.9 to 69.4 ± 2.7 bpm, mean ± SEM, P = 0.004). Only minimal respiratory reflexes were invoked by the bladder volume changes. Conclusion: In lightly anesthetized humans, the acute changes in bladder volume produce only mild cardiovascular and respiratory responses.