The optimal injection time of alfentanil for blunting circulatory responses to tracheal intubation.

BACKGROUND: The aim of this study is to investigate the optimal injection time of alfentanil during induction of anesthesia to blunt the circulatory responses induced by laryngoscopy and tracheal intubation. METHODS: Seventy-five patients of ASA class I or II were randomly assigned to five groups. Group I was the placebo group in which the patients received normal saline 2 ml just before induction. Patients in groups II, III, IV and V received alfentanil 10 microg/kg at 5, 3, 1 and 0.5 min before intubation respectively. Anesthesia was maintained with 1.5% isoflurane and nitrous oxide in 50% oxygen (2:2 L/min). The patients' heart rate and blood pressure before and after intubation were documented and compared. The occurrence of adverse effects was also recorded. RESULTS: Patients' demographic data, baseline hemodynamic profile and the laryngoscopic time did not differ among the five groups. The patients in groups II, III and IV showed decreased heart rate compared with group I within 3 min after intubation. The patients in group V like those in group I did not show a reduction in heart rate 1 min after intubation. The patients in groups II, III, IV and V all showed reduced systolic blood pressure and rate-pressure product (RPP) 2 min after intubation. The occurrence of hypotension and bradycardia was not different among the five groups; hypertension and high RPP were less in groups II, III and IV as compared with group I. Ninety-three percent patients in group II and group III suffered from dizziness after alfentanil administration. One patient in group II had nausea and another one patient displayed hypoxemia after alfentanil administration. CONCLUSIONS: Considering equal effectiveness and fewer side effects, one minute before intubation is the optimal injection time of alfentanil to blunt the circulatory responses induced by laryngoscopy and tracheal intubation.