Powerful techniques in perioperative pain management (Proceedings)

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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.

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).

Mandibular Nerve Block

The mandibular nerve block is very easy to perform and very inexpensive. The mandibular foramen is located on the medial aspect of the mandible, at the transition from the vertical portion to the horizontal portion of the mandible. We slide the needle, usually a 22ga., 1.5 inch needle, along the interior aspect (medial or oral surface) of the mandible to a site about ½ way across that surface (easy to see the foramen on a skull or in a textbook figure). The block can be performed either from inside or outside the oral cavity. Obviously, this nerve block should be performed AFTER induction of anesthesia, but should be done BEFORE surgery is begun.

Mandibular Nerve Block

Blocking the Inferior Alveolar Branch blocks the mandible, lower teeth, and lip. Insert the needle at the lower angle of the jaw, rostral to the angular process, and advance dorsally to the mid-portion on the medial aspect of the mandible. Aspirate, and then deposit the drug at the surface of the bone. The usual dose range is 0.1-1.0 ml bupivacaine or the dental anesthetic Septocaine (preferred) at lower volume. Doses have not yet been adequately defined.

Declaw Analgesia Fore Limb Blocks

Distal Fore Limb Blocks (declaw analgesia blocks) are performed at a level just proximal to the carpus to block the Superficial Radial Nerve (dorsomedial carpus), Ulnar Nerve (branches), lateral carpus, Median Nerve, Ulnar Nerve (branch) on the palmar carpus adjacent to the accessory carpal pad. Deposit 0.1-0.3 ml Bupivacaine 0.5% at each site.

Note: Never use locals containing epinephrine (e.g. Septocaine or lidocaine with epinephrine) for any extremities or tissues with terminal arterial supply (nothing involving the feet, ears or tail)!

Intra-Articular Stifle Block

For the Intra-articular Stifle Block, a 1" 22g needle is used. With the patient in lateral recumbency, with the affected limb uppermost, flex the stifle and apply digital pressure to the medial side of the straight patellar ligament. Insert the needle on the opposite side of the straight patellar ligament midway between the patella and the tibial tuberosity and direct it obliquely and distally toward the intercondylar space of the tibia.

Distention of the joint is noted during injection with the long-lasting local anesthetic Bupivacaine 0.5%. This provides 3-6+ hours of duration with a dose 0.2 ml/kg (0.1 ml/lb). Injection is made both pre-op and post-op for best effect.

Wound Diffusion or Soaker Catheters

This is a powerful, effective, easy and cheap way to deliver local anesthetics right to the site of nociceptive transduction and primary afferent transmission. Catheters are commercially available or can be easily fabricated. Elastomeric pumps , syringes and a variety of other devices can be applied to control delivery of local anesthetic to the wound.

Lidocaine Intravenous CRI (constant rate infusion) for dogs

Provides an analgesic contribution and reduction in anesthetic requirements. The reduced inhalant anesthetic requirement improves blood pressures and is prokinetic. There is also possible anti-inflammatory contribution. This is a very cost-effective analgesic contribution to opioid analgesics.

Lidocaine loading dose of 1-2 mg/kg is administered by slow IV injection over three minutes. Constant Rate Infusion is provided at 20-100 micrograms/kg/minute (0.05-0.1 mg/kg/min) by syringe pump or by controlled drip.

Easy set-up method is as follows: 68 cc of 2% lidocaine is added to a liter bag of IV fluid, administered at 1cc/pound/hour will provide 50 micrograms/kg/min. Adjust between 0.5 and 2.0 cc/pound/hr. Reduce or discontinue if clinical signs of intolerance or overdose occur: nausea, CNS stimulation (twitching or seizures).

Other CRI options for analgesia include: low-dose ketamine, fentanyl, or morphine. A combination of analgesics, one of our favorites, is lidocaine and fentanyl (1:1 mixture) adjusting the rate as needed. Begin at 50 mcg/kg/min for lidocaine and 7.5 mcg/kg/min fentanyl which is achieved at an infusion rate of 0.3 ml/kg/hr of the 1:1 mixture of lidocaine and fentanyl. Adjust the infusion rate as needed to achieve and balance the desired analgesia and sedation.

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