Anesthesia and Analgesia
What this domain tests
Anesthesia and Analgesia tests preanesthetic assessment, drug selection across the anesthetic period, physiologic monitoring, multimodal pain management, and emergency response. Calculations and recognition of complications appear frequently.
Preanesthetic assessment and drugs
- Obtain history, physical examination, and a minimum database; assign an ASA physical status from I to V.
- Premedication commonly combines an opioid (hydromorphone, buprenorphine, methadone) with a sedative (acepromazine, midazolam, dexmedetomidine); anticholinergics are added for specific bradyarrhythmias.
- Induction agents include propofol, alfaxalone, and ketamine; maintenance is usually isoflurane or sevoflurane.
- Preoxygenate when indicated, secure the airway, confirm tube placement, and inflate the cuff just enough to seal.
Monitoring
- Track heart rate, respiratory rate, mucous membrane color, capillary refill time, pulse quality, blood pressure, SpO2, ETCO2 (roughly 35–45 mmHg), and temperature.
- Depth clues include jaw tone, palpebral reflex, and eye position.
- Hypotension with mean arterial pressure below about 60 mmHg warrants checking anesthetic depth, giving a fluid bolus as directed, and considering vasopressor support.
- Bradycardia, hypoventilation, and hypothermia are common and treatable.
Analgesia
- Use multimodal analgesia: opioid plus NSAID plus local block where appropriate, guided by a validated pain scale.
- Local anesthetic ceilings are critical: lidocaine about 4–6 mg/kg in dogs and lower in cats; bupivacaine about 2 mg/kg. Calculate the volume before drawing up.
Worked example
An 18 kg dog is induced with propofol at 4 mg/kg. Dose: 18 × 4 = 72 mg. Propofol is 10 mg/mL, so 72 ÷ 10 = 7.2 mL. Draw up 7.2 mL, give roughly half rapidly to effect, then titrate the remainder while monitoring respiration, and have the endotracheal tube ready. Reasoning: titrating to effect prevents overdose in a patient whose required dose varies with premedication and health status.
Traps that cost marks
- Forgetting that 2% lidocaine contains 20 mg/mL, leading to overdose.
- Missing a falling SpO2 or rising ETCO2.
- Using acepromazine when hypotension is a major concern, such as shock or trauma.
- Failing to check for a cuff leak or to confirm tube placement.
- Neglecting active warming during and after anesthesia.