Alfaxalone alone or combined with midazolam or ketamine in dogs: intubation dose and select physiologic effects

Objective To determine the intubation dose and select physiologic effects of alfaxalone alone or in combination with midazolam or ketamine in dogs. Study design Prospective, clinical study. ANIMALS: Fifty-three healthy client-owned dogs [mean +/- standard deviation (SD)] 5.1 +/- 1.8 years, 27 +/- 15.4 kg, scheduled for elective orthopedic surgery. Methods After premedication with acepromazine (0.02 mg kg(-1)) and hydromorphone (0.1 mg kg(-1)) intramuscularly, alfaxalone (0.25 mg kg(-1)) was administered intravenously over 15 seconds followed immediately by 0.9% saline (AS), midazolam (0.3 mg kg(-1); AM), ketamine (1 mg kg(-1); AK1), or ketamine (2 mg kg(-1); AK2). Additional alfaxalone (0.25 mg kg(-1) increments) was administered as required to permit endotracheal intubation. The incidence of apnea and the time from intubation until spontaneous movement were recorded. Heart rate (HR) and blood pressure were recorded 15 minutes after premedication, after intubation and 2, 5, 10 and 15 minutes thereafter. Blood was collected for measurement of serum glucose and insulin concentrations before induction, after intubation and at 2, 5, 10 and 50 minutes. Data were analyzed by split-plot anova with Bonferroni adjustment for the number of group comparisons. Results Mean +/- SD alfaxalone mg kg(-1) doses required for endotracheal intubation were AS (1.0 +/- 0.4), AM (0.4 +/- 0.2), AK1 (0.5 +/- 0.3) and AK2 (0.5 +/- 0.4) (p=0.0005). Differences in cardiopulmonary variables among groups were minor; HR decreased in AS, while in other groups, HR increased transiently postintubation. Incidence of apnea in AS was 54% with no significant difference among groups. Midazolam significantly prolonged time from intubation until spontaneous movement (p<0.002). Conclusions and clinical relevance Midazolam and ketamine reduced the alfaxalone dose required for endotracheal intubation. Serum glucose and insulin concentrations were not influenced by administration of alfaxalone alone or when administered with midazolam or ketamine.