Effects of Ketamine HCl-Xylazine HCl Combination on Cardiovascular and Pulmonary Values of the Rhesus Macaque (Macaca mulatta)

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Abstract
SUMMARY: Rhesus monkeys (Macaca mulatta) were anesthetized with 4% thiamylal sodium and then surgically prepared (instrumented) to record mean arterial blood pressure, heart rate, arterial Po2 and Pco2, venous Po2 and Pco2 and rectal temperature. Arterial blood pH and respiratory rate were manually recorded. Monkeys were placed in a restraint chair and allowed to regain full consciousness. A 30-minute base-line period was recorded and this was followed by an im injection of ketamine (7 mg/kg), xylazine (0.6 mg/kg), or ketamine-xylazine combination; the physiologic values were recorded for 255 minutes. Similar experiments conducted substituting saline solution for the drugs served as controls (saline control), with values recorded for 180 minutes. When compared with one another, there was no significant difference of the 3 anesthetic regimens and saline control values with regard to (1) mean respiratory rate, (2) mean arterial pH, (3) mean arterial Po2, (4) mean arterial Pco2, or (5) mean venous Pco2. Statistically significant effects were expressed by the ketamine-xylazine combination and xylazine alone with regard to mean arterial blood pressure and heart rate. Both regimens exhibited an approximate 46% decrease (P < 0.05) in mean blood pressure and a 32% decrease (P < 0.01) in mean heart rate when compared with saline control and ketamine alone. These effects occurred within 30 minutes of injections being made and gradually returned toward but did not reach base-line values during the experimental period. When compared with control or ketamine values, ketamine-xylazine combination and xylazine significantly decreased mean rectal temperature. Statistically significant effects of the anesthetic agents on blood gases included a 28% maximum increase in venous Po2 at 30 minutes with ketamine, which gradually returned to normal over the 225-minute experimental period (P < 0.05 compared with saline control), and a 26% maximum decrease in venous Po2 at 30 minutes following ketamine-xylazine injection, which value remained depressed throughout the 225-minute experimental period (P < 0.05 compared with saline control). The results indicate that although, clinically, the ketamine-xylazine combination appears to have offsetting pharmacologic effects, vital physiologic factors are being compromised for a long time.