The Effect of Fentanyl Pretreatment on the High Concentration of Isoflurane-induced Circulatory Responses during Induction of Anesthesia

We investigated whether fentanyl pretreatment can attenuate isoflurane-induced circulatory responses and affect changes in norepinephrine (NE) and epinephrine (E) concentration before and during induction. Ten patients scheduled for elective hysterectomy were allocated to two groups of 5 patients each. One group inhaled 5.0% isoflurane (I group), while the other inhaled 5.0% isoflurane and was given fentanyl 2μg/kg intravenously 2min before induction (F group). Anesthesia was induced with thiamylal followed by vecuronium. The lungs were ventilated with 100% oxygen and 5.0% isoflurane by face mask. Arterial blood samples were drawn from a catheter placed in the radial artery. In the I group, a significant increase in heart rate (HR) was found compared with the baseline value (2min before induction). In the F group, this increase in HR was not noted. Change in mean arterial pressure (MAP) was not found in either group during induction. NE concentrations significantly increased with time compared with the baseline value in both groups, with no differences noted between the I and F groups. No change was found in E concentrations in either group. These results suggest that fentanyl attenuates the enhancement of HR from face mask inhalation of a high concentration of isoflurane and that this effect of fentanyl is not caused by attenuation of NE and E release.