ABA Anesthesia Principles & Practices 2 — Questions and Answers
Question 1: Which mechanism best explains the MAC-sparing effect of nitrous oxide when combined with volatile anesthetics?
- Competitive NMDA receptor antagonism reduces overall anesthetic requirement (Correct answer)
- Nitrous oxide increases cerebral blood flow masking volatile agent uptake
- Nitrous oxide binds directly to MAC receptors in the spinal cord
- Second gas effect accelerates volatile agent induction independently
Correct answer: Competitive NMDA receptor antagonism reduces overall anesthetic requirement
Nitrous oxide's NMDA antagonism provides additive analgesia and sedation, reducing the MAC requirement of co-administered volatile agents.
Question 2: A patient with severe mitral stenosis presents for elective surgery. Which hemodynamic goal is MOST important during anesthetic management?
- Maintain sinus rhythm and avoid tachycardia (Correct answer)
- Increase heart rate to maximize cardiac output
- Reduce systemic vascular resistance aggressively
- Induce mild hypervolemia to increase preload
Correct answer: Maintain sinus rhythm and avoid tachycardia
Mitral stenosis limits diastolic filling; tachycardia reduces diastolic time further, causing acute pulmonary edema, so rate control and sinus rhythm are paramount.
Question 3: The phenomenon of 'diffusion hypoxia' after nitrous oxide discontinuation is primarily caused by:
- Rapid outward diffusion of N2O diluting alveolar oxygen (Correct answer)
- Inhibition of hypoxic pulmonary vasoconstriction by N2O
- Direct depression of medullary respiratory centers by N2O
- N2O binding to hemoglobin reducing oxygen carrying capacity
Correct answer: Rapid outward diffusion of N2O diluting alveolar oxygen
Large volumes of N2O rapidly diffuse from blood into alveoli, diluting both oxygen and CO2, necessitating supplemental oxygen at emergence.
Question 4: Which property of a local anesthetic MOST determines its duration of action?
- Protein binding percentage (Correct answer)
- pKa relative to physiologic pH
- Lipid solubility coefficient
- Molecular weight of the compound
Correct answer: Protein binding percentage
Higher protein binding correlates with prolonged duration because the drug remains sequestered at the sodium channel protein, delaying redistribution.
Question 5: During one-lung ventilation, hypoxemia persists despite 100% FiO2. The MOST effective next intervention is:
- Apply CPAP (5-10 cmH2O) to the non-ventilated lung (Correct answer)
- Increase tidal volume on the ventilated lung
- Switch to high-frequency jet ventilation
- Administer inhaled nitric oxide to the ventilated lung
Correct answer: Apply CPAP (5-10 cmH2O) to the non-ventilated lung
Low-level CPAP to the non-dependent lung maintains partial alveolar recruitment while still allowing surgical access, improving V/Q matching.
Question 6: Neostigmine reversal of neuromuscular blockade is contraindicated when the train-of-four (TOF) count is:
- 0 (no twitches present) (Correct answer)
- 1 twitch present
- 2 twitches present
- 3 twitches present
Correct answer: 0 (no twitches present)
With no twitches present, there is near-complete receptor occupancy by the blocking agent; neostigmine cannot overcome this and may cause paradoxical weakness via muscarinic effects.
Question 7: Which volatile anesthetic is MOST associated with nephrotoxicity due to inorganic fluoride production?
- Methoxyflurane (Correct answer)
- Sevoflurane
- Desflurane
- Isoflurane
Correct answer: Methoxyflurane
Methoxyflurane undergoes extensive hepatic metabolism releasing high serum fluoride levels, historically causing high-output renal failure ('methoxyflurane nephrotoxicity').
ABA Anesthesia Principles & Practices 2
Which mechanism best explains the MAC-sparing effect of nitrous oxide when combined with volatile anesthetics?