A COMPARISON OF LUMBAR EPIDURAL AND INTRAVENOUS FENTANYL INFUSIONS FOR POSTTHORACOTOMY ANALGESIA

This double-blind randomised study compared the analgesic efficacy, re spiratory effects, side effects, and pharmacokinetic disposition of 24 hr lumbar epidural and intravenous infusions of the same dosage regim en of fentanyl (1.5 mu g.kg(-1) bolus then 1 mu g.kg(-1).hr(-1) infusi on) in 50 patients after thoracotomy. Patients received either epidura l fentanyl and intravenous normal saline, or epidural normal saline an d intravenous fentanyl, for postoperative analgesia, after a standard low-dose alfentanil and isoflurane general anaesthetic. Visual analogu e pain scores were lower in the epidural group (P < 0.05) only at two hours postoperatively, and there was no difference in the amount of su pplementary morphine self-administered by patient-controlled analgesic pump. A mainly spinal analgesic effect probably occurred in the first few hours since fentanyl was not detectable in the plasma of patients in the epidural group until two hours after bolus injection; its conc entration was less at that time than after intravenous injection (P < 0.05). Thereafter there was no difference in the plasma concentration profiles between the two groups. Seven patients in the epidural group and ten patients in the intravenous group received naloxone for PaCO2 > 50 mmHg, and one patient in the intravenous group had the infusions stopped because of PaCO2 elevation and somnolence. In patients who did not receive naloxone, the epidural route produced better analgesia th roughout the study period (P < 0.01). Indices of respiratory centre fu nction (apnoeas > 15 sec, slow respiratory rate < 10 min(-1), oxyhaemo globin desaturation < 90% and PaCO2) spirometric measures of pulmonary function, haemodynamic variables, morbidity, and other side effects, were similar in both groups, irrespective of naloxone therapy. Patient s who had no respiratory depression and did not require naloxone had b etter analgesia with epidural fentanyl. However, this advantage did no t result in better pulmonary function.