Perioperative Analgesia and Pain Management
Framing multimodal analgesia
Pain management questions reward a mechanism-based approach. Build analgesia from complementary targets: peripheral (local anesthetics, NSAIDs reducing sensitization), spinal (opioids, alpha-2 agonists), and central (opioids, NMDA antagonists, gabapentinoids). Explain why multimodal therapy reduces individual drug doses and side effects, and connect it to preemptive analgesia-treating before the noxious insult limits central sensitization.
Assessment
Know validated tools and their limits: physiologic parameters (heart rate, blood pressure, respiratory rate) are unreliable alone, especially under anesthesia; behavioral and interactive scales are more specific in conscious patients. Species differences matter-cats mask pain, and prey species may not vocalize.
Drug classes and traps
Be able to describe opioid receptor effects (mu agonism: analgesia, respiratory depression, bradycardia; species-specific dysphoria in cats and horses), NSAID COX selectivity and contraindications (renal compromise, GI ulceration, concurrent steroids), local anesthetic toxicity and maximum doses, and alpha-2 sedation-analgesia with its cardiovascular effects. Trap topics include assuming an NSAID provides surgical analgesia alone, giving local anesthetics without calculating cumulative dose across blocks, and misreading opioid-induced mydriasis or excitement as inadequate analgesia.
Worked example
For a dog undergoing ovariohysterectomy: premedicate with an opioid and consider an alpha-2 (weighing cardiovascular status), induce and maintain, then perform a line block or incisional local anesthetic using a calculated mg/kg ceiling, and continue NSAID plus opioid postoperatively. If pain scores remain high, escalate by adding a different mechanism (e.g., NMDA antagonist or additional local technique) rather than repeating the same class.
Key concepts
Receptor pharmacology, sensitization, preemptive analgesia, multimodal planning, validated pain scoring, and species-specific behavior.