Cardiopulmonary effects of alfaxalone-midazolam-hydromorphone or dexmedetomidine-midazolam-hydromorphone before isoflurane anesthesia in healthy rabbits (Oryctolagus cuniculus).

OBJECTIVE

To compare the cardiopulmonary effects of anesthetic premedication with dexmedetomidine, midazolam, and hydromorphone (DMH) versus alfaxalone, midazolam, and hydromorphone (AMH) in healthy adult rabbits under isoflurane anesthesia.

STUDY

DESIGN

Prospective, randomized, masked crossover study.

ANIMALS: Eight healthy adult New Zealand White rabbits.

METHODS

Rabbits were sedated with 0.03 mg kg-1 dexmedetomidine, 1 mg kg-1 midazolam, and 0.1 mg kg-1 hydromorphone (DMH) or 2 mg kg-1 alfaxalone, 1 mg kg-1 midazolam, and 0.1 mg kg-1 hydromorphone (AMH) injected intramuscularly. Anesthesia was induced with 1-5 mg kg-1 ketamine intravenously and maintained with isoflurane. Physiological variables were recorded every 5 minutes during anesthesia. Arterial blood samples for arterial partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) were obtained at baseline, 15 minutes post-premedication, 3 minutes post-preoxygenation, 15, 30, 45, 60 minutes under anesthesia, and 15 minutes post-extubation. Data were compared using generalized estimating equations adjusted with the Benjamini-Hochberg procedure, the Kolomogorov-Smirnov test, paired t-tests, and Wilcoxon signed ranks tests.

RESULTS

Rabbits given DMH had lower heart rates (p < 0.008) and invasive systolic, mean, and diastolic arterial blood pressures (p < 0.016) compared with AMH. Mean arterial pressure was 22 ± 3 mmHg (mean ± standard deviation) higher in the AMH group. The DMH group had higher PaCO2 at 15 minutes post-premedication (p < 0.001) and 15 minutes post-extubation (p < 0.027). There was no significant difference in PaO2 between treatments, but PaO2 increased following 3 minutes of preoxygenation in both groups (p < 0.001). Rabbits given DMH had a higher sedation score (p = 0.011) and a longer time to recover (p < 0.048).

CONCLUSIONS AND CLINICAL RELEVANCE: Rabbits premedicated with DMH were more sedate and, under anesthesia, had significantly more cardiopulmonary depression (heart rate, arterial blood pressure, PaCO2) compared with AMH.