Comparison of two doses of lidocaine constant rate infusion on cardiopulmonary function and recovery in isoflurane-anesthetized horses

Objective To compare cardiopulmonary variables and recovery scores in isoflurane-anesthetized horses undergoing arthroscopy using two different intravenous (IV) lidocaine constant rate infusions (CRI; 50 or 100 μg kg -1 minute -1 ) under intermittent positive pressure ventilation (IPPV) or spontaneous ventilation (SV). Study Design Prospective, randomized, clinical study. Animals Thirty-six client-owned horses, 8–156 months old (range), with body masses of 280–550 kg. Methods Anesthesia protocol consisted of xylazine, ketamine and diazepam, and maintenance with isoflurane and a CRI of dexmedetomidine. All groups were given an IV bolus of lidocaine (2 mg kg -1 ) 15 minutes after induction and were randomized to CRI 50 or 100 μg kg -1 minute -1 under IPPV or SV (groups IPPV50, IPPV100, SV50 and SV100). Lidocaine was stopped before recovery. Cardiopulmonary variables, plasma lidocaine concentrations during anesthesia and recovery, and a numerical and descriptive score for quality of recovery were compared between groups. Data were analyzed using one- or two-way ANOVA or Kruskal-Wallis tests when appropriate. Results SV groups had significantly higher arterial and end-tidal CO 2 tensions and lower pH ( p < 0.0001). Mean arterial blood pressure differed by ≤ 7 mmHg between groups, was significantly higher in SV100 ( p < 0.0001) and IPPV100 ( p = 0.0001) than SV50, and higher in SV100 than IPPV50 ( p = 0.044). Intraoperative lidocaine concentrations were significantly higher ( p = 0.0005–0.049) with the higher CRI, and in all groups decreased significantly by 20 minutes in recovery ( p < 0.0001–0.002). All groups had similar numerical ( p = 0.529), and similar descriptive recovery scores [ p = 0.413; IPPV50; 2 (1,2), IPPV100; 1 (1,3), SV50; 2 (1,2), SV100; 2 (2,3), median (range)], and of good quality. Conclusion and Clinical Relevance Low and high CRI lidocaine resulted in similar cardiopulmonary function and quality of recovery in healthy horses undergoing arthroscopy. Spontaneous ventilation resulted in hypercapnia.