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Perioperative analgesia: surgery doesn't have to be a pain (Proceedings)


No matter what anesthetic protocol is chosen, the addition of adequate analgesia is imperative for safe anesthesia. Most anesthetic agents, including the anesthetic gases, block the brain's response to pain but don't actually block pain. If the pain is severe enough, the brain can still respond and make the animal appear to be inadequately anesthetized. The result is that the vaporizer is turned up and the brain ceases to respond, but the patient is now too deeply anesthetized and can be at a very dangerous physiologic plane. A more appropriate response would be to decrease the pain and maintain anesthesia at a light, safe depth of anesthesia. Thus, pain management isn't just the ethically 'right thing to do', it is also medically the 'right thing to do'.

When designing analgesic protocols, 3 basic tenets of pain management should always be followed: 1) analgesic drugs should be administered preemptively; 2) multimodal analgesia should be used (especially when pain is moderate to severe); and 3) analgesia should continue as long as pain is present or at least until pain can be reasonably tolerated.

     1. Analgesia provided prior to the pain stimulus ("pre-emptive analgesia") is more effective than analgesia provided once pain has occurred because it prevents or alleviates the hypersensitization of the pain pathways. Because animals try to hide pain when at all possible, it is likely that once an animal is exhibiting pain, the hypersensitization process has begun and pain will be more difficult to treat. Preempting pain will decrease the overall intensity of the pain sensation and will increase the effectiveness of analgesic drugs.
          • "From the recent research concerning the mechanisms of nociception, it is clear that it is better to prevent pain than to treat it. This is a somewhat novel idea when applied to treating pain, but the idea of prevention is clearly entrenched in other medical disciplines. Many animals are vaccinated to prevent them from suffering the pain related to particular disease even though the prevalence of many of these diseases is low. We know that every surgical procedure causes some pain to the patient and that some procedures are more painful than others. With the idea of prevention in mind, we must first do everything possible to reduce the factors that potentiate pain perception." Pascoe PJ. Perioperative Pain Management. In, Vet Clin NA, Small Ani Pract, KA Mathews, ed. 2000;30(4):917-932.
     2. Use of a variety of anesthetic drugs, techniques and routes of administration ("multimodal analgesia") capitalizes on the additive or synergistic effects of analgesic drugs and allows us to provide analgesia that is more intense and/or of longer duration than analgesia provided with any one drug used alone. For example, the use of an NSAID with an opioid typically provides greater analgesia than either an NSAID or opioid alone.
     3. Finally, pain must be addressed not only postoperatively but even after the patient has been discharged from the hospital. Many veterinarians feel that animals do not need analgesic drugs once they have left the hospital because the patients tend not to exhibit pain at home. However, we know that animals instinctively hide pain and that pain, even from elective procedures, does not just magically go away once the animal is no longer in the hospital. Instead, the pain dissipates gradually over a period of days to weeks (depending on the severity of the disease, injury or surgery) and the pain that the animal experiences in that time should be addressed. Even if the animal appears 'okay', as scientists, we know that we severed nerves, caused tissue trauma, and induced inflammation and that these sources of pain will undoubtedly cause some discomfort that does not cease as the patient exits our hospital door.
          • "The optimum duration of analgesic therapy after major surgery in companion animals is unknown. In an animal that is receiving analgesics, the apparent absence of pain or distress does not by itself justify discontinuation of therapy. This would be analogous to discontinuing antibiotic treatment the moment a patient's fever breaks." Bernie Hansen, Analgesic Therapy, The Compendium, July1994:868-875.