TO THE EDITOR:
In "The Effect of Local Infiltration with Morphine before Carpal Tunnel Release" (79-A: 551—554, April 1997), Stahl et al. seemingly attempted to extend the indications for morphine by studying the preoperative effect of local infiltration. The morphine was injected in the area of the release after application of the tourniquet but before the incision was made. The results demonstrated that patients who received morphine had more pain during the release and did not have less pain postoperatively than patients who did not receive morphine. Also, the patients who received morphine had weakness and hypotension, which Stahl et al. postulated may have been secondary to the systemic effects of morphine.
Studies have shown that opiate receptors, which are present in nerve terminals, are not activated until inflammation occurs6. Consequently, the injection of morphine preoperatively to prevent or decrease operative pain may be an overextension of this principle4-6. Inflammation is necessary for pain relief with peripheral morphine since inflammation allows the activation of morphine receptors and also increases the level of morphine receptors in the area. In the present study, the morphine was injected before there was inflammation, rendering a peripheral morphine response unlikely.
With release of the tourniquet, hyperemia of the distal exsanguinated area occurs. This could potentially cause so-called washout of any agent. The small amounts of morphine used in this study could then be realized systemically in any hemodynamically unstable patient. Furthermore, washout of the medication also lessens any of the local effects of morphine. Injection of morphine after release of the tourniquet may provide better pain relief with less potential for systemic side effects.
Douglas E. Garland, M.D.: Southern California Center for Sports Medicine, Memorial Orthopaedic Surgical Group, 2760 Atlantic Avenue, Long Beach, California 90806
George F. Khoury, M.D.: Long Beach Community Hospital, 1720 Termino Avenue, Long Beach, California 90804
Dr. Stahl, Dr. Ben-David, and Dr. Moscona reply:
We fully agree that in experimental models of peripheral opiate analgesia an inflammatory response is necessary in order to demonstrate an analgesic benefit. However, the degree to which a peripheral inflammatory response occurs intraoperatively is open to discussion and was clearly a question intrinsic to our study. It has been recommended that instillation of the opiate at the conclusion of arthroscopy be followed by a few minutes of continued tourniquet occlusion in order to allow fixing of the opiate to local receptors3. The implication is that, by the time of the release, there is already an inflammatory response and expression of opiate receptors. In our clinical model, there would have been negligible washout before the release, so there would have been no appreciable difference between injection at the beginning of the operation and that at the end of the operation (before release of the tourniquet). It was, in fact, our concern about washout that led us to use this particular model. We had previously shown, in a non-tourniquet operative model (rhinoplasty), that there was increased acute pain and bleeding and no late analgesic benefit when morphine was combined with local injection of an anesthetic preoperatively2.
Still, we cannot fully eliminate the possibility that, after release of the tourniquet, the local morphine depot washes out rapidly, before the adequate development of local inflammation and opiate receptors. It remains to be seen if late postoperative intrawound instillation of the opiate or, better still, instillation of a local depot slow-release formulation (such as liposome encapsulation) would be effective.
The confounding effect of local release of histamine caused by the morphine also cannot be ignored. Intradermal injection of a local anesthetic with morphine produces hyperalgesia compared with a non-injected reference site and is associated with a local reaction of redness, swelling, and pruritis suggesting release of histamine1. The local induction of histamine release by morphine makes it a poor choice for exploration of the benefits of peripheral opiate analgesia, and we encourage others to explore the use of opiates other than morphine in the study of this phenomenon.
Shalom Stahl, M.D.; Rony A. Moscona, M.D.: Hand Surgery Unit (S. S.) and Department of Plastic and Reconstructive Surgery (R. A. M.), Rambam Medical Center, P.O. Box 9602, Haifa 31096, Israel
Bruce Ben-David, M.D.: Department of Anesthesia, Herzlia-Haifa (Horev) Medical Center, Haifa 34341, Israel