[Analgesic effects of epidural morphine, fentanyl and lidocaine]

The analgesic effects of epidurally administered morphine 5 mg (group M, n = 15), fentanyl 100 micrograms (group F, n = 15), 2% lidocaine 60 mg (group L, n = 15) and normal saline (group S, n = 10) were investigated in 55 patients scheduled for abdominal surgery. Each drug was prepared in 3 ml solution and was injected though an epidural catheter introduced 3 cm cephalad into the epidural space at T10-11. Analgesic effects were assessed by changes in the dull pain sensation induced by electrical stimulation at 3 Hz through a pair of stainless needles which were placed subcutaneously at T7 and T10 dermatomes. In group M, analgesic effects at T10 were demonstrated in 12 of 15 subjects and the onset of analgesia was more rapid at T10 than at T7. The mean onset time of analgesia was 7.8 +/- 3.6 (mean +/- SD) min. There were 5 subjects in group F and 6 in group L who showed more rapid onset of analgesic effects at T10 than at T7, respectively. There were 2 subjects in group F and 5 in group L, with more rapid onset of analgesia at T7 than at T10. There were several subjects in group F and L with simultaneous onset of analgesia at T7 and T10. In group L, the mean distribution of analgesic area, confirmed with pinprick, was 5.2 +/- 1.9 (mean +/- SD) dermatomal segments. Hypercapnea, associated with somnolence, was frequently seen in group F. None of the subjects in group M, L or S showed such incidents. These results suggest that the main site of action of epidural morphine is located in the spinal cord while that of epidural fentanyl in the brain.