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Objective: To evaluate the effect of a constant rate infusion of ketamine on cardiac index (CI) in sheep, as estimated using noninvasive cardiac output (NICO) monitoring by partial carbon dioxide rebreathing, when anesthetized with sevoflurane at the previously determined minimum alveolar concentration that blunts adrenergic responses (MACBAR)., Animals: 12 healthy Dorset-crossbred adult sheep., Procedures: Sheep were anesthetized 2 times in a balanced placebo-controlled crossover design. Anesthesia was induced with sevoflurane delivered via a tight-fitting face mask and maintained at MACBAR. Following induction, sheep received either ketamine (1.5 mg/kg IV, followed by a constant rate infusion of 1.5 mg/kg/h) or an equivalent volume of saline (0.9% NaCl) solution (placebo). After an 8-day washout period, each sheep received the alternate treatment. NICO measurements were performed in triplicate 20 minutes after treatment administration and were converted to CI. Blood samples were collected prior to the start of NICO measurements for analysis of ketamine plasma concentrations. The paired t test was used to compare CI values between groups and the ketamine plasma concentrations with those achieved during the previous study., Results: Mean ± SD CI of the ketamine and placebo treatments were 2.69 ± 0.65 and 2.57 ± 0.53 L/min/m2, respectively. No significant difference was found between the 2 treatments. Mean ketamine plasma concentration achieved prior to the NICO measurement was 1.37 ± 0.58 µg/mL, with no significant difference observed between the current and prior study., Clinical Relevance: Ketamine, at the dose administered, did not significantly increase the CI in sheep when determined by partial carbon dioxide rebreathing.

Objective: To compare oxygenation and ventilation in white-tailed deer (Odocoileus virginianus) anesthetized with two treatments with and without oxygen supplementation., Study Design: Randomized, blinded, crossover study., Animals: A total of eight healthy adult white-tailed deer weighing 49-62 kg., Methods: Each deer was anesthetized twice intramuscularly: 1) treatment XK, xylazine (2 mg kg -1 ) and ketamine (6 mg kg -1 ) and 2) treatment XTZ, xylazine (2 mg kg -1 ) and tiletamine-zolazepam (4 mg kg -1 ). With the deer in sternal position, arterial and venous blood was collected before and at 30 minutes during administration of oxygen at 1 L minute -1 through a face mask. PaO 2 and heart rate (HR) were compared using two-way repeated measures anova. pH, PaCO 2 and lactate concentration were analyzed using mixed-effects linear models, p < 0.05., Results: When breathing air, PaO 2 was < 80 mmHg (10.7 kPa) in six and seven deer with XK and XTZ, respectively, and of these, PaO 2 was < 60 mmHg (8.0 kPa) in three and five deer, respectively. With oxygen supplementation, PaO 2 increased to 128 ± 4 and 140 ± 5 mmHg (17.1 ± 0.5 and 18.7 ± 0.7 kPa), mean ± standard error, with XK and XTZ, respectively (p < 0.001). PaO 2 was not significantly different between treatments at either time point. HR decreased during oxygen supplementation in both treatments (p < 0.001). Lactate was significantly lower (p = 0.047) with XTZ than with XK (2.2 ± 0.6 versus 3.5 ± 0.6 mmol L -1 ) and decreased (p < 0.001) with oxygen supplementation (4.1 ± 0.6 versus 1.6 ± 0.6 mmol L -1 ). PaCO 2 increased in XTZ during oxygen breathing., Conclusions and Clinical Relevance: Treatments XK and XTZ resulted in hypoxemia, which responded to oxygen supplementation. Both treatments are suitable for immobilization of white-tailed deer under the study circumstances., (Copyright © 2021 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Minimizing sympathetic stimulation under anesthesia prevents activation of the neuroendocrine stress response. The minimum alveolar concentration blunting adrenergic responses in 50% of the population when exposed to a noxious stimulus is defined as MAC-BAR. The purpose of this study was to determine the MAC-BAR of sevoflurane (MAC-BAR sevo ) in sheep and the MAC-BAR sparing effects of ketamine. Thirteen healthy Dorset-cross adult ewes, 4 ± 1 year old and weighing 74 ± 9 kg, were enrolled in a randomized blinded crossover study design. Ewes were anesthetized twice for MAC-BAR sevo determination. After face mask induction with sevoflurane, sheep received intravenous ketamine at 1.5 mg/kg and a constant rate infusion of 1.5 mg/kg/h or an equivalent volume of saline (placebo). After 8 day washout, the other treatment was administered. A bracketing technique was used for MAC-BAR sevo determination and values were collected in duplicate. The mechanical stimulus (sponge forceps) was applied at the coronary band for 1 min and blood was collected for ketamine plasma concentrations. The MAC-BAR sevo values of each treatment were compared using a paired t-test. Mean MAC-BAR sevo of the ketamine and placebo were 2.73 ± 0.23% and 2.77 ± 0.31%, respectively and no significant difference was found (p = .638). Average ketamine plasma concentrations was 1.54 ± 0.18 μg/mL maintained through the study. Ketamine at 1.5 mg/kg, followed by 1.5 mg/kg/h, did not decrease the MAC-BAR sevo in sheep. Further studies to determine the effect of higher doses of ketamine on inhalational anesthetic agents and their potential adverse effects are warranted., (Copyright © 2019 Elsevier Ltd. All rights reserved.)