Cardiovascular responses caused by the combination of lidocaine and vecuronium in the induction of general anaesthesia

Fentanyl, vecuronium and enflurane may cause bradyarrhythmias during anaesthesia. Lidocaine administered before endotracheal intubation may interact synergistically with these agents. In this randomized and double-blind study, lidocaine 1 mg kg-1 (24 patients) or saline (20 patients) was given, immediately after glycopyrrolate 5 micrograms kg-1, fentanyl 1.5 micrograms ml-1 and thiopentone 3-5 mg kg-1, together with vecuronium 0.1 mg kg-1 as a rapid i.v. injection to healthy (ASA 1) surgical patients. Enflurane 0.8% was included in the inhaled gases 10 min and enflurane 1.6% 25 min after lidocaine administration. The plasma concentrations of lidocaine rose to a mean level of 3.1 micrograms ml-1 (maximum 7.1 micrograms ml-1) which may affect the electrical conduction at various sites in the heart. There were no statistically significant differences in arterial blood pressures or heart rates during anaesthesia between the groups. The incidence of junctional rhythm was 7/24 patients in the lidocaine group and 5/20 patients in the saline group. Three patients in the lidocaine group, and two patients in the control group developed junctional rhythm immediately after intubation. The plasma concentrations of vecuronium were unaffected by lidocaine. The ratio of the unbound lidocaine to plasma protein bound lidocaine was at the expected level and did not differ significantly 2 and 10 min after the injection.