[Clinical studies on the peripheral effect of opioids following knee surgery. A literature review].
In this article 34 randomized controlled trials examining peripherally mediated opioid effects after knee surgery are discussed. All studies examined small doses of morphine injected intraarticularly at the end of knee surgery, but not all studies did show an analgesic effect of the peripheral opioid. Because of differing study designs a meta-analysis of the data is not possible. Some important factors like those that the respective authors try to explain the contradictory results with are discussed here: The used concentrations, volumes and doses of morphine are not of major importance. An addition of adrenaline to the study drug, as well as the use of a tourniquet and the time interval between the intra-articular injection and tourniquet release do not seem crucial either. The use of intra-articular drainage (which is opened 10 min after injection of the study drug) and of patient-controlled analgesia as an evaluative method also do not seem to play a major role. But it is remarcable that peripheral opioid effects have often been described after general and local anesthesia but only once after regional anaesthesia. It may be that the activation or expression of peripheral opioid receptors is inhibited by the blockade of input to the central nervous system. Animal experiments are needed to clarify this issue. But it may also be that postoperative pain after regional anaesthesia does not reach a level high enough to make an analgesic effect measurable. If patients after regional anesthesia are not considered, 20 studies out of 29 were able to demonstrate opioid effects whereas 9 were not: The work of Heard and coll. as well as Ruwe and coll. must be criticized because of methodological shortcomings. In the remaining 7 studies the patients of the comparative groups only show low pain scores which may make it impossible to measure an analgesic effect by intraarticular morphine. In summary it can be concluded that very small doses of morphine injected intra-articularly after knee surgery do exert an analgesic effect. In some studies this effect lasted even up to 48 h. But at least during the first two hours the effect is small or else doubtfull. Therefore a combination with bupivacain, a local anesthetic which acts rapidly but only for some hours can be recommended. Most authors testing this combination found it most useful.
Meiser
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A
Klinik für Anaesthesiologie, St. Josef-Hospital, Ruhr-Universität Bochum.
Laubenthal
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H
D000701:Analgesics, Opioid / Q000627:therapeutic use*; D006801:Humans; D007717:Knee / Q000601:surgery*; D010149:Postoperative Pain / Q000188:drug therapy* / Q000517:prevention & control
D000701:Analgesics, Opioid