Comparative Cardiopulmonary and Anesthetic Effects of Ketamine-Medetomidine and Ketamine-Xylazine in Cougars (Felis concolor)
Ten (five female, five male) captive-born cougars (Felis concolor) weighing 45±11 kg (x±SD) were immobilized to determine the cardiopulmonary effects of an i.m. ketamine- (Ketaset, Ft. Dodge Animal Health, Ft. Dodge, Iowa, USA) (2.2±0.2 mg/kg) medetomidine (Domitor, Pfizer Animal Health, Exton, Pennsylvania, USA) (43.4±5.4 µg/kg) combination. In a second trial, 6 mo after completion of the first trial, eight (four female, four male) of the same animals were immobilized with i.m. ketamine- (8.4±2.9 mg/kg) xylazine (Butler Co., Columbus, Ohio, USA) (1.8±0.4 mg/kg). Immediately following immobilization cougars were placed in lateral recumbency and respiratory rates, heart rates, functional oxygen hemoglobin saturation (SpO2) and end-tidal CO2 concentrations were determined every minute for the first 5 min and every 5 min thereafter for 30 min. Arterial blood pressures were determined every 5 min throughout the period of immobilization. Arterial blood samples were collected at 1, 15 and 30 min of immobilization.
Induction time with ketamine-xylazine was significantly longer (19±8 min) than with ketamine-medetomidine (9±3 min). No significant changes in heart rate were seen during the period of immobilization and between groups. A significant decrease in respiratory rates when compared to values obtained at 1 min of immobilization was seen in both groups after 5 min of immobilization and thereafter. Arterial blood pressures were well maintained and no significant changes were seen over time and between groups. Pulse oximeter readings indicated functional oxygen hemoglobin saturation (SpO2) to be <90% during the first 2 min of immobilization in the ketamine-medetomidine group, indicating hypoxemia. For the remainder of the event SpO2 readings were >90%. No periods of hypoxemia were seen in the ketamine-xylazine group with pulse oximeter readings >90% throughout the period of immobilization. End-tidal CO2 concentrations were <35% throughout the anesthetic event in both groups. Arterial blood gas variables indicated no periods of hypoxemia (PO2<60 mm Hg) in both groups during the immobilization period. Reversal with atipamezole (Antisedan, Pfizer Animal Health, Exton, Pennsylvania, USA) given half i.v. and half s.c. (five times medetomidine dose) or 248±0.1 µg/kg in the ketamine-xylazine group, administered 30 min after immobilization was significantly more rapid (4±2 min) and smoother in the ketamine-medetomidine group than in the ketamine-xylazine group (15±9 min).
It is concluded that the cardiopulmonary effects of ketamine-medetomidine and ketamine-xylazine at the dosages used in this study are similar, although ketamine-medetomidine may cause more pronounced respiratory depression. Quality and time to induction and recovery, as well as muscle relaxation were better in the ketamine-medetomidine group.