Continuous intravenous lidocaine infusion during isoflurane anaesthesia in horses undergoing surgical procedures

The aim of the present study was to evaluate the adjunction of lidocaine as a continuous intravenous (IV) infusion during general anaesthesia with isoflurane in a clinical setting. For this purpose sixty horses (ASA I-III) undergoing elective surgery were assigned to a prospective, blinded, randomized clinical trial. After induction of anaesthesia, isoflurane end-tidal concentration was set at 1.3% and subsequently adjusted to maintain surgical plane of anaesthesia. Horses assigned to the group ISO-L (n=40) received IV lidocaine (1.5 mg kg-1, followed by 2.4 mg kg-1 hr-1, reduced later to 2 mg kg-1 hr-1) until 15 minutes before the end of the anaesthesia, while the control group ISO (n=20) received physiologic saline solution. All horses were ventilated mechanically. Mean arterial pressure (MAP) was maintained over 70 mmHg by IV infusion of dobutamine when necessary. Recovery quality was scored from one (very good) to five (very poor). The isoflurane concentration required in ISO-L group decreased down to 24% less (1.2% vs. 1.57%, P<0.05) than in the ISO group with time. Physiological parameters were similar in both groups. Recovery phases were scored of slight, but significant poorer quality (P=0.034) in horses receiving lidocaine (2, IQR 1-3) than in the control group (1, IQR 1-2), although the quality was still acceptable. The use of a continuous IV infusion of lidocaine at 2-2.4 mg kg-1 hr-1 during general anaesthesia allowed for 24% reduction of the isoflurane requirement, without relevant difference in clinical cardiovascular parameters. Under the condition of the present study, the administration of lidocaine tended to reduce moderately the quality of recovery from anaesthesia.