MAC Pharmacology & Physiology in Anesthesia 5 — Questions and Answers
Question 1: What is the recommended initial bolus of 20% lipid emulsion for local anesthetic systemic toxicity in an adult over 70 kg?
- 0.5 mL/kg
- 1.5 mL/kg (about 100 mL) (Correct answer)
- 5 mL/kg
- 10 mL/kg
Correct answer: 1.5 mL/kg (about 100 mL)
ASRA guidance is a 100 mL bolus over 2-3 minutes for patients over 70 kg (1.5 mL/kg if under 70 kg), followed by an infusion.
Question 2: Which local anesthetic carries the greatest risk of refractory cardiotoxicity?
- Lidocaine
- Ropivacaine
- Bupivacaine (Correct answer)
- Chloroprocaine
Correct answer: Bupivacaine
Bupivacaine binds cardiac sodium channels avidly and dissociates slowly ('fast-in, slow-out'), which causes hard-to-treat arrhythmias.
Question 3: Dantrolene treats malignant hyperthermia by acting on which target?
- Dihydropyridine L-type calcium channel
- Ryanodine receptor (RyR1) on the sarcoplasmic reticulum (Correct answer)
- Nicotinic acetylcholine receptor
- Sodium-potassium ATPase
Correct answer: Ryanodine receptor (RyR1) on the sarcoplasmic reticulum
Dantrolene binds RyR1 and reduces uncontrolled calcium release from the sarcoplasmic reticulum.
Question 4: Which topical anesthetic is most associated with methemoglobinemia?
- Tetracaine
- Lidocaine
- Benzocaine (Correct answer)
- Cocaine
Correct answer: Benzocaine
Benzocaine sprays are a classic cause of methemoglobinemia, along with prilocaine; treatment is methylene blue.
Question 5: Which adverse effect is a recognized concern with ondansetron?
- Extrapyramidal reactions
- QT interval prolongation (Correct answer)
- Malignant hyperthermia
- Severe hypertension
Correct answer: QT interval prolongation
Ondansetron, a 5-HT3 antagonist, can prolong the QT interval in a dose-dependent way.
Question 6: Which sedative gives sedation with minimal respiratory depression through central alpha-2 adrenergic agonism?
- Midazolam
- Propofol
- Dexmedetomidine (Correct answer)
- Methohexital
Correct answer: Dexmedetomidine
Dexmedetomidine acts on alpha-2 receptors in the locus coeruleus and produces arousable sedation while largely preserving respiratory drive.
Question 7: In a patient taking an MAO inhibitor, which opioid is most likely to precipitate serotonin syndrome?
- Morphine
- Hydromorphone
- Meperidine (Correct answer)
- Fentanyl at low doses
Correct answer: Meperidine
Meperidine inhibits serotonin reuptake and can cause severe serotonin syndrome when combined with MAO inhibitors.
