BACKGROUND: Laryngoscopy and tracheal intubation are associated with hemodynamic pressor responses, which can have adverse effects. During anesthesia induction with propofol target-controlled infusion (TCI), we aimed to determine the most appropriate dosage of alfentanil required for intubation, using a steady effect-site concentration of propofol and with the use of vecuronium.

METHODS: Eighty ASA class 1 or 2 patients presenting for elective surgery were allocated at random to one of four groups. Anesthesia was induced in all patients with TCI of propofol target concentration 8 µg /ml, followed by vecuronium (0.12 mg/kg). This was reduced to 5µg/ml when the effect-site concentration had been 4µg/ml. After the effect-site concentrations had reached to 5µg/ml, control group received normal saline, group 1 received alfentanil 10µg/kg, group 2 received alfentanil 20µg/kg, and group 3 received alfentanil 30µg/kg. Laryngoscopy and intubation were performed 90 s later. Heart rate was monitored continuously. Systolic blood pressure, diastolic blood pressure and mean arterial pressure were measured at pre-induction, post-induction (pre-intubation) and post-intubation, respectively. Complications such as hypotention and bradycardia were recorded until 5 minutes had elapsed after tracheal intubation.

RESULTS: Control group showed significant increases associated with tracheal intubation in all hemodynamic variables (P < 0.05). Post-intubation values decreased significantly from pre-induction values in groups 1, 2 and 3 (P < 0.05). In groups 2 and 3, hypotension and bradycardia occurred (zero in group 1) but there were no significant differences in their incidences between the three groups.

CONCLUSIONS: We suggest that alfentanil 10µg/kg constitutes the optimal dosage to obtund the hemodynamic responses to tracheal intubation, using propofol TCI (5µg/ml) and vecuronium for induction of anesthesia.