EFFECT OF INTRAVENOUS LIDOCAINE ON HALOTHANE MINIMUM ALVEOLAR CONCENTRATION IN PONIES

This study investigated the effect of lidocaine i.v. on halothane mini mum alveolar concentration (MAC) in ponies. Six ponies were anaestheti sed with thiopentone and succinylcholine, intubated and anaesthesia ma intained with halothane. Ventilation was controlled and blood pressure maintained within clinically acceptable limits. Following a 2 h equil ibration period, baseline halothane MAC was determined. The ponies wer e then given a loading dose of lidocaine (2.5 or 5 mg/kg bwt) or salin e over 5 min, followed by a constant infusion of lidocaine (50 or 100 mu g/kg/min, or saline, respectively). The halothane MAC was redetermi ned after a 60 min infusion of lidocaine or saline, The baseline halot hane MAC for the control group was mean +/- s.d. 0.93 +/- 0.03 %, and no significant decrease occurred following saline infusion. Lidocaine decreased halothane MAC in a dose-dependent fashion (r = 0.86; P < 0.0 003). The results indicate that i.v, lidocaine may have a role in equi ne anaesthesia.