Muscle relaxation with no effect on oxygen uptake during isoflurane anesthesia?

Abstract

To determine the effects of vecuronium neuromuscular blockade on O2 consumption (VO2) during isoflurane anaesthesia 12 patients were studied. 12 patients (ASA-PS I-II, 37.1 +/- 12.1 yr, 173 +/- 8 cm, 70.1 +/- 8.6 kg), scheduled for urological lower abdominal surgery, received isoflurane-N2O-O2-anaesthesia under steady-state conditions (1.3 MAC). Duration of anaesthesia was 169 +/- 32 min and 0.057 +/- 0.016 mg/kg/h vecuronium were needed. The desired level of neuromuscular transmission was set to 10% of control. This level of neuromuscular blockade was kept constant for 60 min by a negative feedback controlled infusion of vecuronium. VO2 was measured by an indirect calorimetry device (MMC Horizon, STPD). During and after recovery of neuromuscular function anaesthesia was maintained and oxygen measurements were continued. Preanaesthetic values of VO2 were in the predicted range for basal metabolism. Steady-state general anaesthesia lead to an 26-28% reduction of VO2 (Range: 144-232 ml/min) compared to the preanaesthetic values (202-288 ml/min, p < 0.01). Neuromuscular blockade showed no significant effect on O2 uptake. We conclude that in patients with adequate depth of anaesthesia vecuronium-induced neuromuscular blockade does not lead to a further reduction of oxygen consumption, since muscular tone is already reduced by general anaesthesia.