Cardiovascular responses to large doses of alfentanil and fentanyl.

The cardiovascular effects of alfentanil and fentanyl were measured during an i.v. anaesthesia technique administered to 12 patients scheduled for lower abdominal surgery. A single bolus of fentanyl 30 micrograms kg-1 (group I, n = 5) or alfentanil 120 micrograms kg-1 (group II, n = 7) was given after the induction of anaesthesia and repeated 1 h later, immediately before the surgical incision. In the absence of surgical manipulation, both drugs induced a significant bradycardia and decreases in arterial pressure, cardiac index, RCWI and LCWI, while SVI and preload equivalents remained stable. During the surgical procedure the same changes were observed for at least 1 h in group I and for, at most, 20 min in group II. The lack of profound cardiovascular depression and the improvement of the myocardial oxygen demand:supply ratio brought about by fentanyl make it a satisfactory technique for long surgical procedures. Alfentanil provided a similar cardiovascular stability only for 20 min.