Evaluation of anesthesia recovery quality after low-dose racemic or S-ketamine infusions during anesthesia with isoflurane in horses

M. Paula Larenza Equine Department, Vetsuisse-Faculty, University of Zürich, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.

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Simone K. Ringer Equine Department, Vetsuisse-Faculty, University of Zürich, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.

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Annette P. N. Kutter Equine Department, Vetsuisse-Faculty, University of Zürich, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.

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Aude Conrot Dr. E. Gräub Laboratories, Rehhagstrasse 83, CH-3018 Bern, Switzerland.

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Regula Theurillat Department of Clinical Pharmacology, University of Bern, Murtenstrasse 35, CH-3010 Bern, Switzerland.

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Martin Kummer Equine Department, Vetsuisse-Faculty, University of Zürich, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.

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Wolfgang Thormann Department of Clinical Pharmacology, University of Bern, Murtenstrasse 35, CH-3010 Bern, Switzerland.

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Regula Bettschart-Wolfensberger Equine Department, Vetsuisse-Faculty, University of Zürich, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.

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Abstract

Objective—To compare anesthesia recovery quality after racemic (R-/S-) or S-ketamine infusions during isoflurane anesthesia in horses.

Animals—10 horses undergoing arthroscopy.

Procedures—After administration of xylazine for sedation, horses (n = 5/group) received R-/S-ketamine (2.2 mg/kg) or S-ketamine (1.1 mg/kg), IV, for anesthesia induction. Anesthesia was maintained with isoflurane in oxygen and R-/S-ketamine (1 mg/kg/h) or S-ketamine (0.5 mg/kg/h). Heart rate, invasive mean arterial pressure, and end-tidal isoflurane concentration were recorded before and during surgical stimulation. Arterial blood gases were evaluated every 30 minutes. Arterial ketamine and norketamine enantiomer plasma concentrations were quantified at 60 and 120 minutes. After surgery, horses were kept in a padded recovery box, sedated with xylazine, and video-recorded for evaluation of recovery quality by use of a visual analogue scale (VAS) and a numeric rating scale.

Results—Horses in the S-ketamine group had better numeric rating scale and VAS values than those in the R-/S-ketamine group. In the R-/S-ketamine group, duration of infusion was positively correlated with VAS value. Both groups had significant increases in heart rate and mean arterial pressure during surgical stimulation; values in the R-/S-ketamine group were significantly higher than those of the S-ketamine group. Horses in the R-/S-ketamine group required slightly higher end-tidal isoflurane concentration to maintain a surgical plane of anesthesia. Moderate respiratory acidosis and reduced oxygenation were evident. The R-norketamine concentrations were significantly lower than S-norketamine concentrations in the R-/S-ketamine group.

Conclusions and Clinical Relevance—Compared with R-/S-ketamine, anesthesia recovery was better with S-ketamine infusions in horses.

Abstract

Objective—To compare anesthesia recovery quality after racemic (R-/S-) or S-ketamine infusions during isoflurane anesthesia in horses.

Animals—10 horses undergoing arthroscopy.

Procedures—After administration of xylazine for sedation, horses (n = 5/group) received R-/S-ketamine (2.2 mg/kg) or S-ketamine (1.1 mg/kg), IV, for anesthesia induction. Anesthesia was maintained with isoflurane in oxygen and R-/S-ketamine (1 mg/kg/h) or S-ketamine (0.5 mg/kg/h). Heart rate, invasive mean arterial pressure, and end-tidal isoflurane concentration were recorded before and during surgical stimulation. Arterial blood gases were evaluated every 30 minutes. Arterial ketamine and norketamine enantiomer plasma concentrations were quantified at 60 and 120 minutes. After surgery, horses were kept in a padded recovery box, sedated with xylazine, and video-recorded for evaluation of recovery quality by use of a visual analogue scale (VAS) and a numeric rating scale.

Results—Horses in the S-ketamine group had better numeric rating scale and VAS values than those in the R-/S-ketamine group. In the R-/S-ketamine group, duration of infusion was positively correlated with VAS value. Both groups had significant increases in heart rate and mean arterial pressure during surgical stimulation; values in the R-/S-ketamine group were significantly higher than those of the S-ketamine group. Horses in the R-/S-ketamine group required slightly higher end-tidal isoflurane concentration to maintain a surgical plane of anesthesia. Moderate respiratory acidosis and reduced oxygenation were evident. The R-norketamine concentrations were significantly lower than S-norketamine concentrations in the R-/S-ketamine group.

Conclusions and Clinical Relevance—Compared with R-/S-ketamine, anesthesia recovery was better with S-ketamine infusions in horses.

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