Influence of two administration rates of propofol at induction of anaesthesia on its relative potency in cats: a pilot study

Objectives This was a randomised, blinded trial to investigate the influence of administration rate on the dose of propofol required for the orotracheal intubation of cats. Methods Twenty-four female domestic cats undergoing ovariohysterectomy were premedicated with oral tramadol (6 mg/kg) or intramuscular tramadol (4 mg/kg), and intramuscular dexmedetomidine (0.007 mg/kg). Oral or intramuscular (IM) tramadol was administered 60 or 30 mins prior to induction of anaesthesia, respectively. Dexmedetomidine was administered 30 mins prior to anaesthetic induction. Sedation scores were established prior to anaesthesia induction with propofol intravenously at 4 mg/kg/min (fast) or 1 mg/kg/min (slow) to effect until orotracheal intubation was achieved without coughing. If coughing occurred, the intubation process was paused for 15 s. Four groups were determined: IM tramadol/propofol fast (GIMF, n = 6); IM tramadol/propofol slow (GIMS, n = 6); oral tramadol/propofol fast (GOF, n = 6); oral tramadol/propofol slow (GOS, n = 6). The Shapiro-Wilk test was used to evaluate for normality of residuals. Sedation scores and propofol anaesthetic induction doses were compared between GIMF and GIMS groups, and between GOF and GOS groups using the Mann-Whitney test and the t-test, respectively (P = 0.05). The presence of hypotension (mean arterial blood pressure <60 mmHg) or apnoea (no breathing for 30 s or more) within the first 15 mins postintubation was recorded. Results The median sedation scores for GIMF and GOF were not significantly different compared with those for GIMS (P = 0.94) and GOS (P = 0.70). However, the mean SD propofol anaesthetic induction doses were higher in GIMF (9.1 +/- 1.8 mg/kg) and GOF (7.9 +/- 1.7 mg/kg) than in GIMS (5.1 +/- 1.5 mg/kg; P <0.01) and GOS (5.4 +/- 0.3 mg/kg; P <0.01). No hypotension or apnoea were detected. Conclusions and relevance Using the slower anaesthetic induction rate resulted in an increase in propofol relative potency.