A comparison of respiratory function in pigs anaesthetised by propofol or alfaxalone in combination with dexmedetomidine and ketamine

BACKGROUND: General anaesthesia in pigs maintained with intravenous drugs such as propofol may cause respiratory depression. Alfaxalone gives less respiratory depression than propofol in some species. The aim of the investigation was to compare respiratory effects of propofol–ketamine–dexmedetomidine and alfaxalone–ketamine–dexmedetomidine in pigs. Sixteen pigs premedicated with ketamine 15 mg/kg and midazolam 1 mg/kg intramuscularly were anaesthetised with propofol or alfaxalone to allow endotracheal intubation, followed by propofol 8 mg/kg/h or alfaxalone 5 mg/kg/h in combination with ketamine 5 mg/kg/h and dexmedetomidine 4 µg/kg/h given as a continuous infusion for 60 min. The pigs breathed spontaneously with an FIO(2) of 0.21. Oxygen saturation (SpO(2)), end-tidal CO(2) concentration (PE′CO(2)), respiratory rate (f(R)) and inspired tidal volume (V(T)) were measured, and statistically compared between treatments. If the SpO(2) dropped below 80% or if PE′CO(2) increased above 10.0 kPa, the pigs were recorded as failing to complete the study, and time to failure was statistically compared between treatments. RESULTS: Alfaxalone treated pigs had significantly higher respiratory rates and lower PE′CO(2) than propofol treated pigs, with a f(R) being 7.3 /min higher (P = 0.01) and PE′CO(2) 0.8 kPa lower (P = 0.05). SpO(2) decreased by 0.6% and f(R) by 1.0 /min per kg increase in body weight in both treatment groups. Three of eight propofol treated and two of eight alfaxalone treated pigs failed to complete the study, and times to failure were not significantly different between treatments (P = 0.75). CONCLUSIONS: No major differences in respiratory variables were found when comparing treatments. Respiratory supportive measures must be available when using both protocols.