The effects of prolonged ketamine-xylazine intravenous infusion on arterial blood pH, blood gases, mean arterial blood pressure, heart and respiratory rates, rectal temperature and reflexes in the rabbit
Wyatt, J.D.; Scott, R.A.; Richardson, M.E.
Laboratory Animal Science 39(5): 411-416
1989
ISSN/ISBN: 0023-6764 PMID: 2530398 Document Number: 346657
The prolonged and safe maintenance of general anesthesia in rabbits with commonly used injectable agents is difficult. Protracted, stable anesthesia with short recovery time has been described in humans using continuous intravenous infusion of ketamine with or without sedatives, muscle relaxants and paralytics. This study evaluated the anesthetic plane achieved and respiratory and cardiovascular effects produced with a ketamine-xylazine intravenous infusion in New Zealand White rabbits. Ten female rabbits were anesthetized with intramuscularly administered ketamine hydrochloride (35 mg/kg) and xylazine hydrochloride (5 mg/kg) after the preanesthetic, baseline measurements of arterial blood pO2, pCO2 and pH and heart and respiratory rates were recorded. The above parameters as well as mean arterial blood pressure, righting, palpebral, pedal, and jaw reflexes were monitored ten minutes after the intramuscularly administered dosage and throughout 4 hours of infusion. Results showed moderate hypotension (21.2% deviation from normal, p < 0.008) and profound hypoxemia (45% deviation from baseline, p < 0.001) 10 minutes after the intramuscularly administered induction dosage. Then, the 4 hour infusion of ketamine (1 mg/minute) and xylazine (0.1 mg/minute) was started. Hypotension progressed (49.1% deviation from normal, p < 0.008), but hypoxemia and hypercarbemia gradually improved with no resultant change (p > 0.1) in arterial pH. There was no significant change (p > 0.1) in respiratory rate but varying qualities of respiration were observed. Both mean arterial pO2 and pCO2 values returned to baseline within 20 minutes after completion of infusion. Heart rate and rectal temperature remained stable during the trial. The righting reflex was abolished in all rabbits throughout the study. The other reflexes that were lost initially slowly returned to most rabbits by the end of infusion. It was concluded that ketamine-xylazine continuously intravenous infusion is an effective means of maintaining a light, nonsurgical plane of anesthesia for up to 4 hours. Although rapid and full recovery occurs, the profound hypoxemia and hypotension associated with both the intramuscular induction and intravenous infusion dosages of ketamine and xylazine may be physiologically detrimental and influence experimental data adversely.