How a dog's weight affects propofol anesthesia dose

Abstract

OBJECTIVE: To determine if body condition score (BCS) influences the sedative effect of intramuscular (IM) premedication or the dose of intravenous (IV) propofol required to achieve endotracheal intubation in dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: Forty-six client-owned dogs undergoing general anaesthesia. METHODS: Dogs were allocated to groups according to their BCS (BCS, 1 [emaciated] to 9 [obese]): Normal-weight Group (NG, n = 25) if BCS 4-5 or Over-weight Group (OG, n = 21) if BCS over 6. Dogs were scored for sedation prior to IM injection of medetomidine (5 μg kg(-1) ) and butorphanol (0.2 mg kg(-1) ) and twenty minutes later anaesthesia was induced by a slow infusion of propofol at 1.5 mg kg(-1)  minute(-1) until endotracheal intubation could be achieved. The total dose of propofol administered was recorded. Data were tested for normality then analyzed using Student t-tests, Mann-Whitney U tests, chi-square tests or linear regression as appropriate. RESULTS: Mean ( ± SD) propofol requirement in NG was 2.24 ± 0.53 mg kg(-1) and in OG was 1.83 ± 0.36 mg kg(-1) . The difference between the groups was statistically significant (p = 0.005). The degree of sedation was not different between the groups (p = 0.7). Post-induction apnoea occurred in 11 of 25 animals in the NG and three of 21 in OG (p = 0.052). CONCLUSIONS: Overweight dogs required a lower IV propofol dose per kg of total body mass to allow tracheal intubation than did normal body condition score animals suggesting that IV anaesthetic doses should be calculated according to lean body mass. The lower dose per kg of total body mass may have resulted in less post-induction apnoea in overweight/obese dogs. The effect of IM premedication was not significantly affected by the BCS. CLINICAL RELEVANCE: Induction of general anaesthesia with propofol in overweight dogs may be expected at lower doses than normal-weight animals.