Incorporating analgesia into anesthetic protocol (Proceedings)

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Incorporating analgesia into anesthetic protocol (Proceedings)

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Aug 01, 2010

A. No matter what anesthetic protocol is chosen, the addition of adequate analgesia is imperative for safe anesthesia and for enhanced patient outcome. Perioperative analgesia has two monumental advantages:
     1. Analgesia increases anesthetic safety by decreasing the necessary dosages of anesthetic drugs. 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.

     2. Analgesia improves our medical success rate because adequate analgesia improves healing and allows a decreased incidence of postoperative stress-related complications. Pain initiates a fairly profound stress response and a sympathetic overdrive. Stress and autonomic imbalance are not benign and the cascade of side effects include gastrointestinal (GI) ileus, GI ulceration, clotting dysfunction, hypertension, tachycardia, tachyarrhythmias, and many others. Furthermore, stress and pain cause a fairly marked increase in cortisol release and a substantial increase in energy requirements, the latter of which may lead to a negative nitrogen balance and both of which impair healing.

Thus, pain management isn't just the ethically 'right thing to do', it is also medically beneficial.

B. 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.

     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.