Effect of administration rate on propofol requirement in cats

Objectives The objective of this study was to determine the effect of administration rate on propofol dose for induction of anesthesia and the effect of methadone on this dose. Methods This was a prospective, randomized, blinded clinical study. Forty male cats (mean ± SD age 1.5 ± 0.8 years) were admitted for orchiectomy. Cats were randomly allocated to receive acepromazine (0.05 mg/kg) with either methadone (MET; 0.3 mg/kg) or saline (SAL; 0.03 ml/kg). Each premedication group then received anesthetic induction with propofol at 5 (F) or 1.5 mg/kg/min (S), resulting in the following four groups: MET-F, SAL-F, MET-S and SAL-S. Sedation scores were assigned at 15 and 30 mins after premedication using a simple descriptive scale (SDS) and a visual analog scale (VAS). After assignment of sedation scores, respiratory frequency ( f_R) was recorded, and anesthetic induction began and was continued until cats lost their palpebral reflexes and jaw tone, and the eye globe rotated ventromedially. The time for induction and the total amount of propofol needed was recorded, and intubation was then performed. After intubation, f_R was also recorded. Results SDS and VAS sedation scores were low at 15 and 30 mins after premedication. There was no significant difference in sedation scores by time or between the groups at any time on any scale. The amount of propofol needed to achieve anesthetic induction was 5.3 ± 1.1 mg/kg in group MET-F, which was statistically lower when compared with the other three groups, which demonstrated no difference among them. Conclusions and relevance Premedication with acepromazine and methadone was not able to produce adequate sedation in healthy cats. The slow induction rate is not adequate for use in cats considering that all of the animals demonstrated excitement during anesthetic induction. The fast administration rate was able to produce adequate induction of anesthesia and reduce the amount of propofol needed to achieve intubation only when using methadone.