Annals of medicine
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The concept and value of 'multimodal' or 'balanced' analgesia in the treatment of postoperative pain is reviewed. Based upon the relatively few multimodal studies compared to unimodal studies, it is concluded that a combination of analgesics will improve pain relief including movement-associated pain. Since analgesic combination therapy is rational, further studies are needed to evaluate the optimal combination for each surgical procedure, as well as to assess the risk of side effects and need for surveillance in large-scale studies.
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Patient-controlled analgesia (PCA) is a newer technique for pain management. Patients are allowed to self-administer small analgesic bolus doses into a running intravenous infusion, intramuscularly, subcutaneously or even into the epidural space. Demands are usually controlled by computer-driven infusion pumps, but can also be delivered by disposable devices. ⋯ PCA has proved its importance for pain studies, e.g. for algesimetry, to determine predictors of postoperative pain, to describe drug interactions, to evaluate the concept of pre-emptive analgesia or for pharmacokinetic designs. It is concluded that PCA results have been urgently required in order to change the mind of physicians and nursing staff with respect to individual pain management strategies. Once this goal is achieved, PCA concepts should also be used for the improvement of more conventional techniques.
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Basic scientific evidence suggests that an analgesic intervention made before surgery will produce a better outcome than the same intervention made after surgery. The evidence from randomized controlled trials (RCTs) which tested this hypothesis in patients is reviewed. Four studies with paracetamol or NSAIDs did not show any pre-emptive effect. ⋯ The opioid studies which did show a pre-emptive effect had other technical weaknesses. One way to combat lack of power would be to combine data (meta-analysis). This is very difficult in this field because of the outcome measures which investigators are using.
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Recent research has demonstrated the increasing importance of the spinal cord in processing and modulating nociceptive input. Different groups of drugs, each acting by a unique mechanism, have been shown to block nociceptive afferent transmission. None of the currently available spinally administered local anesthetics, opioids or non-opioids produce analgesia without side effects. ⋯ Preliminary results suggest that the neuropeptide octreotide has potent analgesic effects. 'Balanced spinal analgesia' using a combination of low doses of drugs, with separate but synergistic mechanisms of analgesia, may produce the best results. The optimal drug combinations and dosages remain to be determined. It is essential that animal neurotoxicity studies followed by controlled clinical trials are performed before widespread spinal administration of new drugs.
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This paper describes the responses of peripheral and central visceral nociceptive systems to acute injury and discusses these observations in relation to the concept of 'pre-emptive analgesia'. Visceral nociceptors are known to respond to injury but are also known to become sensitized to non-noxious stimuli during the inflammatory process that follows intense noxious stimulation. ⋯ Therefore it is proposed that the concept of 'pre-emptive analgesia', as such, has no neurophysiological basis. Any analgesic procedure aimed at reducing postoperative pain must not only prevent the arrival in the CNS of the initial afferent barrage evoked in nociceptive endings but also reduce or eliminate the persistent discharges of sensitized nociceptors during the inflammatory repair process that are critically important for the maintenance of the central pain state.