Background and objective: This prospective, randomized, double-blinded study was designed to compare the effects of remifentanil or fentanyl on anaesthetic induction characteristics of propofol, thiopental or etomidate.

Methods: Seventy-two patients were enrolled in six groups of 12 individuals each. In three groups, fentanyl was given as a bolus dose of 1.5 μg kg−1, whereas the others received a remifentanil infusion at 0.5 μg kg−1 min−1. Five minutes later, propofol, thiopental or etomidate were titrated to a state of unresponsiveness. Assessment included the amounts of drug necessary for induction, haemodynamics and the times to apnoea, loss of eyelash reflex, and the release of a water-filled syringe held in the patient's hand.

Results: Induction times to loss of the eyelash reflex were significantly shorter in the remifentanil than in the fentanyl groups: with propofol 50.7 ± 13.6 s (mean ± SD) versus 74.9 ± 27.0 s (P < 0.01), with thiopental 42.9 ± 16.8 s versus 77.2 ± 27.8 s (P < 0.01) and with etomidate 54.7 ± 17.6 s versus 72.3 ± 24.0 s (P < 0.05). The times to respiratory arrest or for the syringe to fall were significantly shorter with remifentanil than with fentanyl for propofol and for thiopental, but not for etomidate. In terms of dosages per kg body weight necessary to achieve unresponsiveness, less propofol (−29%, P < 0.05), thiopental (−25%, P < 0.05) or etomidate (−32%, P < 0.01) was necessary with remifentanil than with fentanyl. Haemodynamic responses to tracheal intubation were controlled more effectively with remifentanil. However, within the remifentanil groups, mean arterial pressure significantly decreased during induction: −26% with propofol,−18% with thiopental and −14% with etomidate (all P < 0.01).

Conclusions: During anaesthetic induction, a remifentanil infusion of 0.5 μg kg−1 min−1 over 5 min is a suitable alternative to a 1.5 μg kg−1 bolus dose of fentanyl: induction times are shorter with reduced amounts of propofol, thiopental or etomidate.