Cardiovascular function during maintenance of anaesthesia with isoflurane or alfaxalone infusion in greyhounds experiencing blood loss

ObjectiveTo compare adequacy of oxygen delivery and severity of shock during maintenance of anaesthesia with isoflurane or alfaxalone infusion in greyhounds experiencing blood loss. Study designProspective, randomised study. AnimalsTwenty-four greyhounds (ASA I). MethodsAll greyhounds were premedicated with methadone (0.2mg kg(-1)) intramuscularly. Anaesthesia was induced with alfaxalone 2.5mg kg(-1)intravenously. Following endotracheal intubation, the dogs were connected to an anaesthetic circle circuit delivering oxygen. Dogs were allocated to receive inhaled isoflurane or an intravenous infusion of alfaxalone for maintenance of anaesthesia. Isoflurane was initially administered to achieve an end-tidal concentration of 1.4% and alfaxalone was initially administered at 0.13mg kg(-1)minute(-1). The dose of isoflurane or alfaxalone was adjusted during instrumentation to produce a clinically equivalent depth of anaesthesia. All dogs were mechanically ventilated to normocapnia (PaCO2 35-40mmHg; 4.67-5.33 kPa). Passive warming maintained core body temperature between 37 and 38 degrees C. Measured and calculated indices of cardiovascular function, including mean arterial blood pressure (MAP), cardiac index (CI), systemic vascular resistance index (SVRI), oxygen delivery index ((D) over dotO(2)I), oxygen consumption index ((V) over dot O2I) and oxygen extraction ratio (OER), were determined at baseline (60minutes after start of anaesthesia) and after removal of 32mL kg(-1)and 48mL kg(-1)of blood. ResultsIn all dogs, blood loss resulted in a significant decrease in MAP, CI, (D) over dotO(2) , and a significant increase in SVRI, (V) over dotO(2)I , and OER. The changes in each of the indices did not differ significantly between dogs receiving isoflurane and dogs receiving alfaxalone. Conclusion and clinical relevanceNo difference in oxygen delivery or severity of shock was observed when either inhaled isoflurane or intravenous alfaxalone infusion was used for maintenance of anaesthesia in greyhounds experiencing blood loss. There appears to be no clinical advantage to choosing one anaesthetic agent for maintenance of anaesthesia over the other in a dog experiencing blood loss.