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Pain management for emergency & critical care patients (Proceedings)


Our patient population has changed fairly dramatically in the last 10 years as our medical skills have progressed and we have become capable of supporting patients with advanced disease and advancing age. Furthermore, our surgical skills have improved and surgery now is often complicated, long and may involve major blood loss and/or major physiological manipulation. Now we must hone our anesthesia and pain management skills in order to support patients that largely don't fit into the 'young, healthy' category and to support patients throughout difficult surgical procedures. It is no longer appropriate to think that safe anesthesia means recovering as many patients as we anesthetize. Instead, we need to focus on what happens to the patient during the anesthetic period - which starts when the patient is admitted for anesthesia and really doesn't end until the patient has returned to 'normal' and free of pain (or at least comfortable). Necessary advances in anesthesia include better preparation of the patient for anesthesia (including the use of pre-anesthetic tranquilizers and analgesic drugs), improved support of the patient during the anesthetic period (including better monitoring and the use of IV fluids) and increased attention to events in the recovery period (including emergence delirium and bouts of pain).

Principles of analgesia:

Also, no matter what anesthetic protocol is chosen, analgesia is imperative. Perioperative analgesia has two monumental advantages: 1) analgesia increases anesthetic safety by decreasing the necessary dosages of anesthetic drugs and 2) analgesia improves our medical success rate because adequate analgesia improves healing and allows a decreased incidence of postoperative stress-related complications. Regardless of which analgesic drugs are chosen, 3 basic tenets of pain management should always be followed: 1) analgesic drugs should be administered preemptively; 2) multimodal analgesia should be used whenever possible; and 3) analgesia should continue as long as pain affects the patient's quality of life.

My favorite drugs for compromised patients:

Reminder: All tranquilizers, induction drugs and inhalant drugs cause some degree of dose-dependent CNS depression and most cause both respiratory and cardiovascular depression. In healthy patients, many of the physiologic effects of anesthetic drugs are well tolerated or can be counteracted by routine measures such as administration of oxygen or intravenous (IV) fluids. In compromised patients, these effects can be exacerbated, further contributing to the demise of the patient. Successful anesthesia in compromised patients is highly dependent on adequate patient stabilization, diligent patient support and monitoring, and the use of appropriate anesthetic agents at appropriate dosages.

Sedatives / tranquilizers

1.Opioids - Butorphanol, buprenorphine, morphine, hydromorphone, oxymorphone, fentanyl
     • Advantages: Provide moderate to profound analgesia, safe, reversible, many are inexpensive, provide sedation, versatile (can be administered PO, IM, IV, SQ, in the epidural space, in the intra-articular space, etc…)
     • Disadvantages: Controlled substances, may provide more sedation than desired (rare), relatively short duration of action
     • NOTE: Opioid-induced respiratory depression is highly overrated. In animals, respiratory depression is almost always related to degree of sedation - in which case, ALL sedatives can be respiratory depressants.

2. Benzodiazepines - Diazepam (Valium®) and Midazolam (Versed®)
     • Advantages: minimal to no cardiovascular or respiratory effects, reversible
     • Disadvantages: won't provide adequate sedation when used alone in young, healthy or excited dogs, no analgesia.

3. Acepromazine – not commonly used in compromised patients; can contribute to hypotension (the exception is patients with upper airway compromise that need long-term sedation and some patients with cardiovascular disease that would benefit from a reduction in afterload).

4. Alpha-2 agonists – not commonly used in compromised patients; will cause an increase in cardiac work (however, they are reversible drugs so they may be appropriate for some critical patients but certainly not for any patient with hemodynamic compromise).

Induction drugs

1. Propofol
     • Advantages: rapid induction and recovery, multiple routes of clearance from the body, good muscle relaxation
     • Disadvantages: somewhat expensive, must be administered IV, causes mild to moderate respiratory and cardiovascular depression

2. Ketamine
     • Advantages: inexpensive, can be administered IM, mild respiratory depression, no cardiovascular depression in heart-healthy patients
     • Disadvantages: can cause cardiovascular depression in patients with cardiovascular compromise, controlled drug, can cause muscle rigidity

3. Etomidate
     • Advantages: no cardiovascular changes
     • Disadvantages: expensive, poor muscle relaxation, vocalization

4. Inhalant induction is not appropriate
     • The dose of the inhalant is entirely too high (side effects of inhalants are dose-dependent), the induction will be stressful and will be prolonged.