PLASMA FENTANYL CONCENTRATIONS AND CLINICAL OBSERVATIONS DURING AND AFTER OPERATION

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Abstract
Patients undergoing major abdominal gynecological surgery (30) were anesthetized with a standard technique, including N2O in O2 and myoneural blockade. The lungs were ventilated with large tidal volumes (10 ml/kg) but PaCO2 [CO2 partial pressure] remained within normal limits. Fentanyl was given as a loading dose of 10 .mu.g/kg or 25 i.v. at the start of the anesthetic. The lower dose was followed by an infusion of fentanyl (2 .mu.g/min) or by fentanyl given as increments of 100 .mu.g after 30 min and 50 .mu.g after 1 h. Significant (2% level) 2nd peaks of plasma fentanyl (increases > 0.49 ng/ml) occurred within 45 min of the end of surgery in 60% of patients receiving the infusion, in 40% of patients receiving the high dose and in 20% of patients receiving increments of fentanyl. Analgesia was required in the first 3 h after operation in 70% of the patients in the infusion group, in 60% in the high dose group and in 80% in the increment group. The mean times for administration of postoperative analgesia in the 3 groups were 102, 80 and 55 min, respectively. After operation PaO2 [O2 partial pressure] was < 8 kPa in 60-67% of the patients. Particular care should be given to patients who are breathing air and recovering from anesthesia in which fentanyl in large or recurring amounts was used, since administration of analgesics after operation may produce additive effects and further arterial hypoxemia.