Systemic fentanyl enhances the spread of spinal analgesia produced by lignocaine

Seventy-one patients undergoing transurethral prostatectomy under spinal anaesthesia were allocated randomly to one of four groups; fentanyl-naloxone (F-Nal), fentanyl-normal saline (F-NS), normal saline-naloxone (NS-Nal), and normal saline-normal saline (NS-NS) group. Twenty minutes after subarachnoid injection of hyperbaric lignocaine 100 mg, we tested the level of spinal analgesia (pinprick sensation) and administered i.v. either fentanyl 100 micrograms (F-Nal and F-NS groups) or normal saline 2 ml (NS-Nal and NS-NS groups). Ten minutes later, we assessed the new levels of analgesia and administered i.v. either naloxone 0.4 mg (F-Nal and NS-Nal groups) or normal saline 1 ml (F-NS and NS-NS groups). The level of sensory block was reassessed 10 min after the naloxone or normal saline treatment. Ten minutes after i.v. administration of fentanyl or normal saline, the level of analgesia increased in the F-Nal and F-NS groups by 3.98 and 3.78 cm, respectively, and differed significantly compared with the NS-Nal and NS-NS groups (both P less than 0.01). Forty minutes after spinal block, the decrease in analgesia in the F-Nal group (3.97 cm) differed significantly from that in the other groups (P less than 0.01). Systemic fentanyl enhanced the spread of analgesia. This enhancement was antagonized by naloxone.