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Powerful techniques in perioperative pain management (Proceedings)

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Apr 01, 2009

When to Treat Pain - Newly available analgesics and novel methods for the use of standard medications have greatly expanded options for safe and effective relief of pain in veterinary patients. Analgesic therapy should be considered an integral part of our care when there is a reasonable possibility that pain might result from a medical procedure or condition. The best results are obtained when the analgesics are given before surgery. The key concept is "pre-emptive analgesia". Recognizing pain in animals requires consideration of overt signs and subtle behavioral changes. As in people, individual analgesic requirements and responses vary with the animal and the peculiarities of each situation through recovery from surgery or critical illness. Therefore, always "dose to effect."

Pre-emptive Analgesia - The best results are obtained when the analgesics are given before surgery. New routes and methods of drug administration are being developed and validated. These include patient-controlled analgesia (PCA) for humans, trans-dermal opioids (patches), controlled release gels, and neuroaxial (epidural and spinal) analgesics.

Multi-Modal Analgesia - Combination of pain-management methods works much in the same way that we can use anesthetic agents in various combinations for the best patient care. For "balanced analgesia" this may be represented in using some opioid as a pre-anesthetic and post-operative analgesic, along with use of a local anesthetic block. Or perhaps a pre-operative opioid, a local anesthetic infusion both during and after surgery, and an NSAID post operatively. Multi-modal or balanced analgesia has been shown to greatly improve analgesia with fewer side effects than might result from a more massive dose of any single analgesic medication.

Local Anesthetic Regional Analgesia Techniques

Techniques for use of local and regional anesthetics in small animal patients are easily learned and applied to substantially reduce the doses of other anesthetics and analgesics needed. These techniques are very cost-effective and greatly improve patient care. In combinations with other strategies (e.g. opioids, NSAID's, dissociative anesthetics) for preventing and relieving clinical pain, these anesthetic/analgesic procedures contribute to "balanced" analgesia or "multi-modal" analgesia.

To avoid toxic effects, the total volume of bupivacaine (0.5%) or lidocaine (2%) should always be less than 0.4 ml/kg or 0.2 ml/lb. Signs of an overdose include nausea, twitching or possibly seizures. At higher doses, cardiac depression can occur, particularly with overdoses or accidental IV injections of bupivacaine. To minimize the risk of accidental IV injections, always aspirate before injection.

Epidural Injection

Landmarks are the Iliac crests, dorsal midline, and dorsal lumbar vertebral spinous processes.

Drugs used are typically preservative-free morphine (e.g. Duramorph), designed for epidural use, as the best-recommended product. With the preservative-free morphine preparation, cost is substantially greater than with parenteral morphine. We currently do use the preservative-free morphine, usually in combination with either saline or 0.5% bupivacaine. The Duramorph preparation is at a concentration of 1.0 mg/ml. We administer 1 cc Duramorph per 10 kg body weight (0.1 cc/kg) mixed with either saline or bupivacaine, also at 1 cc per 10 kg, for a total volume of 2 cc per 10 kg.

Brachial Plexus Nerve Block

Produces anesthesia / analgesia distal to the and including the elbow, using bupivacaine at 0.2 ml/kg (0.1 ml/lb) with a 22 ga. 1.5-3.5 inch needle inserted between the shoulder joint and ribs, parallel to vertebrae. Aspirate, inject 0.2cc, withdraw slightly, repeatedly to distribute the bupivacaine. Keys to success include efforts to distribute drug, aspirate to avoid IV injection and toxicity, and minimize volume at each injection site to avoid nerve damage.

Maxillary Nerve Block

The field blocked includes the maxilla, upper teeth, lip, and nose of the injected side.

Insert needle toward the pterygopalatine fossa from the ventral margin of zygomatic arch, 0.5 cm lateral to the lateral canthus of the eye. Aspirate, to rule out vascular injection, and deposit drug at surface of the bone. Dose: 0.1-1.0 ml bupivacaine or Septocaine (preferred).