Abstract
Controversy exists regarding the site of action of fentanyl after epidural injection. The objective of this investigation was to compare the efficacy of epidural and intravenous fentanyl for orthopedic surgery. A randomized double-blind study was performed in Hospital São Paulo. During the postoperative period, in the presence of pain, 29 patients were divided into two groups: group 1 (n = 14) received 100 microg of fentanyl epidurally and 2 ml of saline intravenously; group 2 (n = 15) received 5 ml of saline epidurally and 100 microg of fentanyl intravenously. The analgesic supplementation consisted of 40 mg of tenoxicam intravenously and, if necessary, 5 ml of 0.25% bupivacaine epidurally. Pain intensity was evaluated on a numerical scale and plasma concentrations of fentanyl were measured simultaneously. The percentage of patients who required supplementary analgesia with tenoxicam was lower in group 1 (71.4%) than in group 2 (100%): 95% confidence interval (CI) = 0.001-0.4360 (P = 0.001, Fisher's exact test; relative risk, RR = 0.07). Epidural bupivacaine supplementation was also lower in group 1 (14.3%) than in group 2 (53.3%): 95% CI = 0.06-1.05 (P = 0.03, Fisher's exact test; RR = 0.26). There was no difference in pain intensity on the numerical scale. Mean fentanyl plasma concentrations were similar in the two groups. Intravenous and epidural fentanyl appear to have similar efficacy for reducing pain according to the numerical scale, but supplementary analgesia was needed less frequently when epidural fentanyl was used. NCT00635986.
Highlights
The discovery that opioids act by activating receptors located in the dorsal horn of the spinal cord, and reports of intense and long-lasting pain relief after intrathecal injection of morphine[1] have been important steps for postoperative analgesia.Fentanyl is one of the most widely used opioids administered epidurally
The percentage of patients who required supplementary analgesia with tenoxicam was lower in group 1 (71.4%) than in group 2 (100.0%): 95% confidence interval (CI) = 0.001-0.4360 (Fisher’s exact test, P = 0.04; risk relative, RR = 0.07)
Epidural bupivacaine supplementation was lower in group 1 (14.3%) than in group 2 (53.3%): 95% CI = 0.06-1.05 (Fisher’s exact test, P = 0.05; RR = 0.26)
Summary
Fentanyl is one of the most widely used opioids administered epidurally. Some authors have suggested that its effect is directly mediated in the spinal cord, while others have believed that the main site of action is the supraspinal region, in view of its high liposolubility, with consequent absorption into the systemic circulation and distribution to the brain.[3] Other investigators have suggested a combination of these two mechanisms to explain the action of epidural fentanyl.[4] further studies are necessary to explain the sites of action of this drug when administered epidurally and to determine whether there is any difference in the analgesic effect between applying the drug intravenously and epidurally
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