Perineural injection of morphine fails to relieve postoperative pain in humans.
Ten patients scheduled for bilateral foot surgery were given general anesthesia plus ankle blocks. One side was blocked with 0.02% morphine and the other with 0.9% saline. A second group of 10 patients for bilateral foot surgery had one side blocked with 0.02% morphine and the other with 0.01% morphine. A within-patient blind comparison of postoperative analgesia between the two sides was performed by nurse observers, using categorical and visual analogue scales for both pain intensity and pain relief. Postoperative analgesia recorded by the nurse observer was not significantly different between morphine and saline. Similarly, there was no significant difference in postoperative analgesia between legs blocked with the higher or lower dose of morphine. Thus, perineural morphine does not relieve postoperative pain at doses equivalent to 2-4 mg in a 70-kg man.