Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Ambulatory Anesthesia
INTRODUCTION: Intravenous regional anesthesia (IVRA) is a popular technique for surgical procedures in the ambulatory setting. The identification of opioid receptors in the periphery has prompted speculation that the addition of fentanyl to local anesthetics for IVRA may be helpful. Two previous studies have shown that the addition of fentanyl to a local anesthetic (for a 20 min procedure) was not effective in improving anesthesia [1,2]. In both studies, volunteers were tested on the same arm sequentially on different days. However in a recent abstract, the combination of 0.2% lidocaine, 50 [micro sign]g of fentanyl and 3 mg d-tubocurare for IVRA was as effective in providing IVRA as 0.5% lidocaine alone . In order to facilitate comparison of different treatments and improve intravolunteer reliability, we performed the present comparison of "lidocaine only" and "lidocaine plus fentanyl" with bilateral forearm tourniquets in a single fashion. Since a 5-sec, 50 Hz tetanic stimulus at 60 mA (TET) has been shown to be an equivalent stimulus to surgical incision , we used TET to test the anesthetic adequacy of the opioid/local anesthetic combination.
METHODS: Following IRB approval, 16 healthy, unsedated volunteers underwent IVRA of both forearms. After placement of 20 g IVS and exsanguination with an elastic esmarch bandage, the proximal tourniquets of the double cuffs were inflated simultaneously to 250 mmHg. Each volunteer then received 30 ml of lidocaine 0.5% with 2 ml of saline (L) and 30 ml of lidocaine 0.5% with 2 ml of fentanyl (100 [micro sign]g total) (L + F) in a double-blind fashion. Two cutaneous electrodes were placed over the ulnar nerve at each wrist for TET. After 30 minutes, the distal tourniquets were inflated, followed by release of the proximal tourniquets. Verbal analogue pain scores (VAS) to TET were recorded every 5 min until complete loss of sensation. Pain responses to TET were compared using analysis of variance and paired t-test; p < 0.05 was considered statistically significant.
RESULTS: All 16 volunteers developed complete anesthesia in both forearms within 10 min. There was no significant difference in pain scores between the two arms among the 16 volunteers (Figure 1). Time to complete loss of sensation to TET was 37 +/- 23 min (mean +/- SD, range 10 - 70 min) in the L only arm and 48 +/- 16 min (range 5 - 85 min) in the L + F arm (P=NS).
DISCUSSION: The findings of this investigation confirm prior reports that the addition of fentanyl to IVRA with lidocaine does not improve the effectiveness of anesthesia during the first 20 minutes [1,2]. Even when the possible analgesic effects of fentanyl were followed longer than 20 minutes, fentanyl offered no benefit. Our results are consistent with the hypothesis that although opioid receptors are located in the periphery, they typically are not accessible in the absence of mechanisms which increase their exposure (e.g. inflammation) .
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