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Cardiopulmonary effects and anaesthesia recovery quality in horses anaesthetized with isoflurane and low‐dose S‐ketamine or medetomidine infusions

Menzies, M Paula Larenza, Ringer, Simone K, Conrot, Aude, Theurillat, Regula, Kluge, Katharina, Kutter, Annette PN, Jackson, Michelle, Thormann, Wolfgang, Bettschart‐Wolfensberger, Regula
Veterinary anaesthesia and analgesia 2016 v.43 no.6 pp. 623-634
acepromazine, air, anesthesia, blood pressure, flunixin, heart rate, horses, intravenous injection, isoflurane, ketamine, medetomidine, oxygen, prospective studies, surgery, thiopental
To evaluate cardiopulmonary effects and anaesthesia recovery quality in horses anaesthetized with isoflurane receiving medetomidine or S‐ketamine infusions.Randomized, blinded, prospective clinical trial.Fifty horses undergoing elective surgery.After acepromazine and flunixin meglumine premedication, horses received medetomidine (7 μg kg−1) intravenously (IV). Anaesthesia was induced with midazolam and racemic ketamine (Med treatment group; 2.2 mg kg−1; n = 25) or S‐ketamine (S‐ket treatment group; 1.1 mg kg−1; n = 25) IV and maintained with isoflurane in oxygen/air and medetomidine (Med; 3.5 μg kg−1 hour−1) or S‐ketamine (S‐ket; 0.5 mg kg−1 hour−1). All horses were mechanically ventilated. Cardiopulmonary variables were evaluated. Isoflurane end‐tidal concentrations (Fe′Iso), dobutamine requirements and thiopental boli were recorded. Plasma samples were collected in six horses to evaluate S‐ketamine and S‐norketamine concentrations. After surgery, medetomidine 2 μg kg−1 was administered IV. Four independent observers scored recovery using a visual analogue scale and a numerical rating scale.Both groups required similar mean Fe′Iso (1%). However, S‐ket horses needed more thiopental boli. Median intraoperative cardiac index values were higher with S‐ket (4.5 L minute−1 m−2) than Med (3.9 L minute−1 m−2). Overall, there were no differences in heart rate, blood pressure or dobutamine requirements; however, horses in S‐ket showed higher heart rate values at 30 minutes after anaesthesia induction. Compared with Med horses, S‐ket horses showed decreased PaO2 and increased pulmonary venous admixture values estimated with the Fshunt calculation. Recoveries were shorter and of poorer quality with S‐ket. During infusion, S‐ketamine and S‐norketamine plasma concentrations lay in the ranges of 0.209–0.917 μg mL−1 and 0.250–0.723 μg mL−1, respectively.Despite the higher intraoperative cardiac index with S‐ket, both protocols were considered to provide acceptable cardiovascular function. However, recovery quality was significantly better in the Med group.