Comparative assessment of the effects of alfentanil, esmolol or clonidine when used as adjuvants during induction of general anaesthesia

Background and objective: This randomized, double-blinded, prospective study compared the effects of clonidine, esmolol or alfentanil on the level of hypnosis and haemodynamic responses to intravenous induction of anaesthesia and endotracheal intubation. Methods: Forty-five patients scheduled for elective surgery were allotted to one of three groups. They were given either alfentanil 3 μg kg-1min-1 (n = 15); esmolol 1 mg kg -1min-1 (n = 16) or clonidine 3 μg kg-1 (n = 14) as a 10 min infusion. The infusions of alfentanil and esmolol, but not of clonidine, were maintained during endotracheal intubation. Anaesthesia was induced with midazolam (2 mg) and thiopental as required to suppress the eyelash reflex. Atracurium (0.5 mg kg-1) was given to produce neuromuscular block. Mean arterial pressure, heart rate, and bispectral index were recorded on arrival (baseline), after study drug infusion, after injecting midazolam and thiopental, as well as after endotracheal intubation. ANOVA and χ2-test were used for analysis. Results: Blood pressure, heart rate and the bispectral index were unaltered by the study drugs, but thiopental requirements were reduced by alfentanil and clonidine (P < 0.014). Mean arterial pressure values (mean ± standard error of mean) in the alfentanil, esmolol and clonidine groups were: baseline: 107.8 ± 3.8; 106.6 ± 3.9; 103.4 ± 3.7 mmHg; after thiopental: 74.0 ± 4.2; 85.6 ± 4.3; 94.2 ± 4.1 mmHg and after endotracheal intubation: 91.7 ± 5.3; 114.1 ± 6.9; 123.6 ± 5.6 mmHg, respectively (two-way ANOVA, P < 0.001). Mean arterial pressure changed significantly after intubation from baseline (P < 0.001) after alfentanil (-15%) and clonidine (+20%) but not after esmolol (+7%), while the changes between pre- and postintubation values were similar in all groups (24-33% increase). The bispectral index indicated that all patients had an adequate level of hypnosis, but the variability was higher in the esmolol group (P < 0.002). Conclusions: None of the study drugs blocked the increase in mean arterial pressure induced by endotracheal intubation, but esmolol provided better overall haemodynamic stability. All groups had an adequate level of hypnosis.