Preoperative opioid consumption increases morphine requirement after leg amputation

The aim of this observational study was to assess the influence of preoperative opioid consumption on postoperative morphine consumption after leg amputation performed under combined regional and general anesthesia.

After Institutional Review Board approval, patients scheduled for leg amputation were included in a prospective observational study. A popliteal sciatic nerve catheter was placed preoperatively and 0.75% ropivacaine 20 mL was injected incrementally. Amputation was performed under general anesthesia. Postoperative analgesia included acetaminophen, a continuous infusion of 0.2% ropivacaine at 7 mL hr(-1), and intravenous morphine if the visual analogue scale (VAS) pain score was >3 on a 0-10 scale. Patients were divided post-hoc into two groups according to their preoperative opioid consumption: yes (Preop opioids) or no (No preop opioid).

Twenty-two patients were included, 12 in the Preop opioids Group and 10 in the No preop opioid Group. The VAS score after catheter insertion and before induction of general anesthesia was zero in both groups. Total postoperative opioid consumption from day 1 to day 3 and daily consumption at day 7 was greater in the Preop opioids Group than in the No preop opioid Group (52 [13-133] mg morphine equivalents vs 0 [0-26] mg; P = 0.02) and (10 [8-25] mg vs 0 [0-0] mg; P = 0.01), respectively, (median [25-75 interquartile values]).

Despite the use of regional anesthesia, chronic opioid consumption before leg amputation is associated with increased postoperative morphine consumption and phantom limb pain.