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MORPHINE HAS NO POSTOPERATIVE PERIPHERAL ANALGESIC EFFECT

Department of Anesthesiology, CHUM – Hôpital Notre-Dame, 1560 Sherbrooke Est, Montréal, Québec, H2L 4M1

INTRODUCTION

Growing clinical and experimental evidence shows a potential role of peripheral exogenous opioids in postoperative pain management.

The aim of this study is to test the hypothesis that morphine, injected into the wound at the end of surgery, improves postoperative pain scores, has an opioid sparing effect and therefore, diminishes narcotic related side-effects.

METHODS

After IRB approval, twenty-three patients undergoing elective gynecological procedures by laparotomy were included in this prospective, randomised and double-blinded trial. Anesthesia was standardised. Immediately before skin closure, the wound was infiltrated with morphine 0,1 mg/kg diluted in saline (total 20 mL) in group Morphine (M) and 20 mL of saline in the Control group (C). Patients in group M had a subcutaneous injection of 2mL of saline in the anterior aspect of the thigh while patients in group C received morphine 0,1 mg/kg diluted in saline (total 2 mL). Thus, every patient having the same amount of systemically available morphine, we could evaluate its local analgesic effect.

Patient Controlled Analgesia (PCA) with morphine was the sole analgesic used during the 24 hours of the study period. We measured pain intensity at rest and during standardized movements, using a Verbal Rating Scale (0 to 10), as well as narcotic related side effects at 1, 4, 8, 12, and 24h following extubation. Total amount of morphine consumption was noted at 12 and 24 h.

RESULTS

Demographic data were similar in both groups. No difference was found between the two study groups regarding postoperative mean morphine demand (M=30mg vs C=30,6mg; p=0,45 at 12h and M=56,5mg vs C=50,6mg; p=0,25 at 24h). Side effects were also comparable. Finally, there was no difference in pain intensity during the 24 hours follow-up except at 4 hours where the median pain score at rest was higher in the M group ( 5,5 compared with 3,5; p=0,02 ).

DISCUSSION

Morphine injected postoperatively, into the wound, after a gynecologic procedure laparotomy shows no advantage over a peripherally administered identical dose and could even slightly increase early postoperative pain. Histamine release and subsequent activation of nociceptors could be a proposed mecanism for this finding

REFERENCES

Anesth Analg. 76:182–91

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