Clinical comparison of two regimens of lidocaine infusion in horses undergoing laparotomy for colic

Objective: To compare, in horses undergoing laparotomy for colic, the effects of administering or not administering a loading intravenous (IV) bolus of lidocaine prior to its constant rate infusion (CRI). Effects investigated during isoflurane anaesthesia were end-tidal isoflurane concentration (Fe′ISO), cardiovascular function, anaesthetic stability and the quality of recovery. Study design: Prospective, randomized clinical study. Animals: Thirty-six client-owned horses. Methods: Horses were assigned randomly to receive lidocaine as a CRI (50 μg kg^-1 minute^-1) either preceded (LB) or not preceded (L) by a loading dose (1.5 mg kg^-1 IV over 15 minutes). Lidocaine infusion (LInf) was started (T0) within 20 minutes after induction of general anaesthesia and discontinued approximately 30 minutes before the end of surgery. Anaesthetic depth, Fe′ISO, intra-operative physiological parameters and quality of recovery were assessed or measured. Data were analysed using one-way anova, t-test, Fisher test, Wilcoxon and Kruskal-Wallis tests as appropriate (p < 0.05). Results: Mean ± SD Fe′ISO was 1.21 ± 0.08% in group LB and 1.23 ± 0.06% in group L. Heart rate was significantly higher in group L than in group LB at times T5-T15, T25, T35 and T95. No difference was found between groups in other measured physiological values, nor in any measure taken to improve these parameters. Recovery phase was comparable and satisfactory in all but one full term pregnant horse in group L which fractured a femur during recovery. Conclusion: Preloading with a lidocaine bolus prior to a CRI of lidocaine did not influence isoflurane requirements, cardiopulmonary effects (other than a reduction in heart rate at some time points) or recovery compared to no preloading bolus. Clinical relevance: A loading dose of lidocaine prior to CRI does not confer any advantage in horses undergoing laparotomy for colic.