Lumbar epidural fentanyl infusions for post-thoracotomy patients: analgesic, respiratory, and pharmacokinetic effects

Ten patients undergoing a thoracotomy were studied for 24 hours postoperatively to determine the effects of a continuous lumbar epidural fentanyl infusion on postoperative pain, arterial blood gases (ABG), respiratory pattern (respiratory inductive plethysmography, RIP), and fentanyl plasma concentration (CONC). Patients served as their own controls because RIP and ABG data were obtained the night prior to surgery during sleep. Epidural fentanyl was administered as a bolus of 1.5 micrograms/kg followed by an infusion of 1.0 micrograms/kg/h started 1 hour after induction. Insufficient analgesia was treated with a bolus of 0.5 micrograms/kg and an infusion increase of 0.25 micrograms/kg/h. Postoperative assessment included RIP, ABG, CONC, and visual analog pain score (PS). The average infusion rate postoperatively was 1.47 +/- 0.08 micrograms/kg/h (114.3 +/- 8.3 micrograms/h). A mean PS of 2.1 +/- 0.3 was achieved; however, there was a delay in attaining this. There was no significant incidence postoperatively of apnea or slow respiratory rate. A significant but clinically insubstantial increase in PaCO2 and decrease in pH occurred. A steady state CONC of approximately 2.0 ng/mL was reached after 9 hours. The PS correlated with CONC in half the patients (0.60 less than r less than 0.86), indicating a systemic component may have contributed to the analgesic effect.