Both propofol and alfaxalone are popular anesthetic induction drugs for cats. This study, possibly the first of its kind, compared the cardiorespiratory effects of alfaxalone to those of propofol for anesthetic induction and maintenance in 20 healthy cats undergoing elective ovariohysterectomy. All patients selected for this randomized, blinded, prospective clinical trial were over 5 months old and were not pregnant or lactating. Prior clinical observations by the researchers suggested that cats receiving alfaxalone for induction and maintenance demonstrated less apnea than those receiving propofol. This study was designed to test the hypothesis that cats receiving a continuous rate infusion (CRI) of alfaxalone for total intravenous anesthesia (TIVA) would experience less apnea, hypercapnia, or hypoxemia, and would need less ventilatory support compared to those receiving a propofol CRI for TIVA.
All patients were premedicated with metdetomidine 0.01 mg/kg intramuscularly and meloxicam 0.3 mg/kg subcutaneously, and then were randomly divided into two groups of 10. No opioids were administered to the patients preoperatively to exclude their potential respiratory depressant effects; methadone was administered after surgery. Group A received alfaxalone 5 mg/kg/minute, followed by 10 mg/kg/hour intravenously, while group P received propofol 6 mg/kg/minute, followed by 12 mg/kg/hour intravenously, respectively, for anesthetic induction and maintenance. These intravenous agents were delivered to the the patients via a syringe pump to avoid human variability associated with manual administration. The cats were connected to a rebreathing system providing 100% oxygen via a cuffed endotracheal tube, and the same surgeon performed all surgeries. The vital signs, arterial hemoglobin oxygen saturation (SpO2), mean arterial pressure (MAP), and end-tidal carbon dioxide (PECO2) were monitored every 5 minutes by the same anesthetist throughout the anesthetic period. The anesthetic maintenance drug rate was adjusted as needed based on physiologic variables and clinical signs. Venous blood gas samples were obtained immediately after intubation and 30 and 60 minutes after induction as well. If a cat demonstrated apnea > 30 seconds, PECO2 > 55 mm Hg, or SPO2 < 90%, then she was ventilated manually.
The researchers found that 80% of the cats on the propofol CRI needed controlled (manual) ventilation, while only 20% of those receiving alfaxalone required controlled ventilation. Based on this information, it appears that in cats alfaxalone has a broader therapeutic range than propofol in terms of less observation of hypoventilation. Group P (propofol) had a higher MAP over time than group A (alfaxalone), suggesting that propofol has less negative inotropic or vasodilatative effects than alfaxalone, but none of the patients in either group demonstrated hypotension, and there was no difference in pulse rate between either group. A PECO2 > 55 mm Hg was observed in 4 of the cats in group P, and in no cats in group A. Low arterial oxygen saturation (SpO2 < 90%) was noted in zero cats in group A and 6 cats in group P. In the 6 group P cats experiencing SpO2 < 90%, the low SpO2 was associated with hypoventilation or apnea rather than changes in cardiovascular parameters. Venous blood gas analysis demonstrated a lower mean pH and higher mean partial pressure of carbon dioxide 30 minutes after induction in group P than in group A.
Based on the results of this study, both propofol and alfaxalone are acceptable agents for anesthetic induction and maintenance in cats, but alfaxalone has fewer adverse effects on respiration than propofol. In situations where either manual or mechanical controlled ventilation is unavailable, alfaxalone may be the preferred anesthetic induction and/or maintenance agent.
