The effects of propofol, isoflurane and sevoflurane on vecuronium infusion rates for surgical muscle relaxation in dogs

Abstract

ObjectiveTo compare the constant rate infusion (CRI) of vecuronium required to maintain a level of neuromuscular blockade adequate for major surgeries, e.g. thoracotomy or laparotomy, in dogs anaesthetized with a CRI of fentanyl and either propofol, isoflurane or sevoflurane. Study designProspective, randomized, cross-over study. Animals Thirteen male beagles (age, 9–22 months; body mass 6.3–11.3 kg). Materials and methodsDogs were anaesthetized with propofol (24 mg kg−1 hour−1 IV CRI; group P), isoflurane (1.3% end-tidal concentration; group I) or sevoflurane (2.3% end-tidal concentration; group S) with fentanyl (5 μg kg−1 hour−1 IV, CRI). Sixty to seventy minutes after induction of anaesthesia, vecuronium was administered at a rate of 0.4, 0.3 and 0.2 mg kg−1 hour−1 in groups P, I and S respectively. To determine the degree of neuromuscular block, a peripheral nerve was stimulated electrically using the train-of-four (TO4) stimulus pattern. Evoked muscle contractions were evaluated using a neuromuscular monitoring device. Once the TO4 ratio reached 0, the continuous infusion rate was decreased and adjusted to maintain a TO4 count of 1. Continuous infusion was continued for 2 hours. The infusion rate of vecuronium was recorded 20, 40, 60, 80, 100 and 120 minutes after the start of infusion. ResultsThe mean continuous infusion rates of vecuronium during stable infusion were 0.22 ± 0.04 (mean ± SD), 0.10 ± 0.02 and 0.09 ± 0.02 mg kg−1 hour−1 in groups P, I and S respectively. There were statistically significant differences between the rates in groups P and I and between the rates in groups P and S. Conclusions and Clinical relevanceIn healthy dogs, the recommended maintenance infusion rate of vecuronium is 0.2 mg kg−1 hour−1 under CRI propofol–fentanyl anaesthesia and 0.1 mg kg−1 hour−1 during CRI fentanyl–isoflurane or sevoflurane anaesthesia