Effect of bolus doses of alfentanil on the arousal response to intubation,as assessed by the auditory evoked response

We have studied the effect of bolus doses of alfentanil on the arousal resp onse to intubation, using the auditory evoked response (AER) of the electro encephalogram (EEG) in 45 anaesthetized patients. After induction of anaest hesia with propofol and 20 min of positive pressure ventilation via a laryn geal mask airway with 0.6 MAC of isoflurane and 50% nitrous oxide in oxygen , patients received saline (control), or alfentanil 15 or 50 mu g kg(-1) be fore intubation. The early cortical AER before and after intubation in each group was measured and compared. After intubation, Pa amplitude increased in the saline group by 60% (95% CI + 10 to + 130), decreased in the low-dos e alfentanil group by 11% (-38 to +29) and decreased further in the high-do se alfentanil group by 26% (-49 to +7). There were significant (P<0.005) li near trends in the three group means for Pa amplitude. Similarly, Nb latenc y increased in the saline group by 30% (-2 to +73), decreased in the low-do se alfentanil group by 10% (-32 to +19) and decreased further in the high-d ose alfentanil group by 19% (-39 to +7). There were significant (P=0.02) li near trends in the three group means for Nb amplitude. Systolic and diastol ic arterial pressures increased after intubation in the control group, and to a lesser extent in the low-dose alfentanil group, but decreased after hi gh-dose alfentanil. Heart rate increased after intubation in the control gr oup but decreased in both alfentanil groups, decreasing to a greater degree in the high-dose group. There were significant (P<0.001) linear trends for all three haemodynamic variables in the three groups. We conclude that the increase in Pa amplitude after intubation was blocked by bolus administrat ion of alfentanil and that this effect was dose dependent.