The peripheral effect of fentanyl on postoperative pain

The clinical value of the analgesic effect of opioids administered peripherally (except for intraarticular administration) has not been clearly demonstrated. The aim of this study was to test the hypothesis that fentanyl, added to a local anesthetic for wound infiltration, can enhance postoperative analgesia via a peripheral mechanism. Patients with inguinal herniorrhaphy performed under spinal anesthesia were randomly assigned to one of two groups (n = 10 each). At the end of surgery, the wound was infiltrated with 10 mt of lidocaine 0.5% and fentanyl 0.001% (10 mu g) in one group; in the other group, the wound was infiltrated with 10 mt of Lidocaine 0.5% alone (and fentanyl 10 mu g IM contralaterally). The following variables were determined in a double-blind manner: the duration of anesthesia (response to a von Prey filament), the duration of analgesia (time to mild postoperative pain), postoperative meperidine consumption, intensity visual analog scale of spontaneous and movement-associated pain 24 h after surgery, and wound pain threshold 24 h after surgery (pressure algometry). The addition of fentanyl for wound infiltration enhanced the duration of anesthesia (130 +/- 37 vs 197 +/- 27 min; P < 0.001) and decreased the intensity of spontaneous (50 +/- 17 vs 19 +/- 18; P < 0.002) and movement-associated (56 +/- 15 vs 26 +/- 21 mm; P < 0.002) pain 24 h postoperatively. Differences between groups for other variables were not statistically significant. Fentanyl added to a local anesthetic for wound infiltration after spinal anesthesia can enhance postoperative analgesia by a peripheral mechanism. Implications: Fentanyl can enhance analgesia by a peripheral mechanism. Added to a local anesthetic for wound infiltration, it may be of benefit for the relief of postoperative pain.