A.M. Troy, R. C. Hutchinson, G.N.C. Kenny

University Department of Anaesthesia, Royal Infirmary, Glasgow

Background and Goal of study: Remifentanil, a powerful opioid, with a rapid onset of action and a context-sensitive half-time of approximately 3 minutes is suited to TCI as it does not accumulate after prolonged infusions.[1] Propofol and remifentanil may provide good intubating conditions without the use of muscle relaxants.[2] We aimed to determine the most appropriate dose of remifentanil required for intubation using a steady effect-site concentration of propofol and whether this would avoid the pressor response associated with laryngoscopy.[3]

Materials and Methods: Following ethics committee approval and written informed consent, 60 ASA I or II patients were enrolled in the study. Oral temazepam was administered one hour preoperatively. Patients were randomised to 3 groups. All patients were induced with propofol TCI set at 6.5 μg ml^-1 which was reduced to 3 μg ml^-1 after 1 minute. Each group received a different target concentration of remifentanil. These were:

Group I- 19 ng ml^-1 reduced to 10 ng ml^-1 after 1 minute,

Group II- 15 ng ml^-1 reduced to 8 ng ml^-1 after 1 minute, and

Group III- 11 ng ml^-1 reduced to 6 ng ml^-1 after 1 minute.

After 3 minutes, the effect-site and target concentrations almost equalled each other. Laryngoscopy and intubation were attempted 4 minutes after induction. Heart rate, blood pressure and oxygen saturations were measured before induction and pre- and post-laryngoscopy/intubation. Intubating conditions, using a standard scoring system, as well as jaw relaxation, glottic exposure, vocal cord position, coughing and patient movement were assessed. Statistical analysis was performed using ANOVA and t-tests.

Results: There was no significant difference in the haemodynamic variables between the groups prior to induction. MAP and heart rate decreased in all groups after induction of anaesthesia. After laryngoscopy the increase in MAP and heart rate was significantly less than the corresponding baseline values. Intubating conditions were considered satisfactory in 30% of Group III, and in 75% each of Groups I and II. Intubation was successful in 15/20, 19/20 and 20/20 patients in Groups III, II and I respectively.

Conclusions: Avoiding the use of muscle relaxants may be beneficial in patients where muscle relaxants may not be desirable, or necessary, for surgery. Remifentanil TCI attenuates the haemodynamic response to laryngoscopy.

1. Kapila A, Glass PS, Jacobs JR, et al. Anesthesiology 1995;83:968-75.

2. Grant S, Noble A, Woods J, et al. Br. J. Anaesth. 1998;81:540-43.

3. Thompson JP, Hall AP, Russell B, et al. Br. J. Anaesth. 1998;80:467-69.