Is there any clinical advantage of increasing the pre-emptive dose of morphine or combining pre-incisional with postoperative morphine administration?

Abstract

Pre-emptive treatment with an i.v. infusion of morphine 10 mg at induction reduces postoperative analgesic requirement and wound hypersensitivity compared with the same dose administered at the end of operation. Increasing the dose of pre emptive morphine may potentially reduce post operative pain further, while administering morphine at the end of operation, in addition to the beginning, may reduce pain generated by the sensory activity elicited from the wound in the immediate postoperative period. To examine this we have conducted a randomized, double-blind study in patients undergoing abdominal hysterectomy to compare the effect of morphine 20 mg administered before operation with 10mg at induction and 10 mg on closure of the peritoneum. Postoperative pain was assessed by visual analogue score (VAS) at rest and on movement and by total morphine consumption administered by patient-controlled analgesia (PCA). Wound sensitivity was assessed by von Frey pain thresholds. Both groups had similar morphine consumption, VAS scores and touch and pain thresholds, and in both, secondary hyperalgesia was prevented. Nausea and vomiting scores were higher in the 20-mg group. There was no significant difference between the two groups and neither regimen appeared to offer obvious clinical advantages compared with a lower dose (10 mg) morphine analgesic strategy. Therefore, there may be a ceiling effect to the production of pre-emptive analgesia by morphine.