Inhalational Anaesthetics (Properties, MAC, Fluorinated Agents, N2O) MCQs

Anaesthesia · 37 free questions with answers & explanations.

1. A volatile anaesthetic agent has an oil:gas partition coefficient of 97 and a blood:gas partition coefficient of 0.45. Which property best explains the rapid emergence from anaesthesia seen with this agent?
2. During prolonged sevoflurane anaesthesia with low fresh gas flows (<1 L/min), a nephrotoxic compound is generated by reaction of the agent with the CO2 absorbent. This compound is:
3. The MAC of isoflurane in a 70-year-old patient at sea level (1 atm) is approximately 1.15%. In a patient with chronic alcoholism on long-term ethanol intake (not acutely intoxicated), the expected MAC would be:
4. Nitrous oxide (N2O) is avoided in patients with pneumothorax, bowel obstruction, and middle ear surgery because it:
5. Which volatile anaesthetic agent has the highest vapour pressure at 20°C, necessitating a heated, pressurised vaporiser (Tec 6) for its delivery?
6. Desflurane differs from isoflurane most significantly in which pharmacokinetic property that makes it preferred for outpatient anaesthesia requiring rapid emergence?
7. Which effect of nitrous oxide on closed gas spaces makes it contraindicated in middle ear surgery?
8. Compound A (methoxyflurane degradation product) is nephrotoxic because it liberates inorganic fluoride. The critical renal injury from inorganic fluoride is primarily due to which mechanism?
9. The dose of inhaled anaesthetic required to maintain immobility (MAC) is reduced in all of the following conditions EXCEPT:
10. Isoflurane is preferred over halothane for neurosurgical procedures because of which specific cerebral haemodynamic advantage?
11. A 45-year-old patient requires maintenance of anaesthesia with sevoflurane. At 1 MAC, what percentage of sevoflurane in oxygen (FiO2 = 1.0) is required?
12. Sevoflurane undergoes degradation in soda lime to produce Compound A. At which carbon dioxide absorbent temperature does this degradation become clinically significant, and what organ is at risk?
13. During desflurane delivery at a vaporiser setting of 6%, the anaesthetist notes tachycardia and hypertension 5 minutes into induction. Which physiological mechanism is responsible?
14. Nitrous oxide diffuses into closed gas spaces faster than nitrogen can exit. Which of the following surgical scenarios is an ABSOLUTE contraindication to N2O use because of this property?
15. The Meyer-Overton hypothesis relates anaesthetic potency to which physicochemical property, and which inhalational agent is the principal exception to this rule?
16. Sevoflurane undergoes degradation in soda lime to produce Compound A (fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether). Compound A is nephrotoxic predominantly through which mechanism?
17. A patient anaesthetised with isoflurane shows end-tidal isoflurane of 1.3% but remains haemodynamically unstable with excessive movement to surgical stimulus. The anaesthetist suspects intraoperative awareness. Which of the following physiological states MOST increases MAC for isoflurane?
18. Which inhalational agent uniquely causes non-shivering thermogenesis to be impaired, contributing to the greatest degree of intraoperative hypothermia compared with other volatile agents at equipotent concentrations?
19. Nitrous oxide (N2O) is contraindicated in a patient with pneumocephalus following posterior fossa surgery. The minimum interval before N2O can be safely re-introduced after craniotomy closure is approximately:
20. The second-gas effect of nitrous oxide accelerates induction with a co-administered volatile agent. The underlying mechanism is:
21. A 72-year-old patient with hepatic cirrhosis (Child-Pugh C) is undergoing elective abdominal surgery. Which inhalational agent is MOST implicated in causing liver necrosis via reductive metabolism under hypoxic conditions?
22. Compound A (hexafluoroisopropanol) formed during sevoflurane degradation is rendered non-toxic by which hepatic process?
23. During low-flow anaesthesia with sevoflurane at fresh gas flow of 1 L/min using soda lime, Compound B accumulates in the circuit. Which clinical feature directly results from prolonged inhalation of high concentrations of Compound B?
24. A patient breathing 50% nitrous oxide for 4 hours is at risk for bone marrow suppression. The mechanism involves irreversible inhibition of which enzyme?
25. The oil:gas partition coefficient of an inhalational agent primarily determines its:
26. Compound A is a halogenated inhalational agent. At a blood:gas partition coefficient of 0.69, it has the fastest induction and recovery of all clinical volatile agents. Which agent is this, and what complication limits its use at high concentrations (>1 MAC) without adequate fresh gas flow?
27. Nitrous oxide (N2O) is 35 times more soluble in blood than nitrogen. During emergence from N2O-based anaesthesia, it rapidly leaves blood into alveoli, diluting alveolar O2. This phenomenon is called:
28. The MAC-awake of an inhalational agent — the concentration at which 50% of patients open their eyes on command — is approximately what fraction of MAC?
29. Desflurane has a blood-gas partition coefficient of 0.42 compared to sevoflurane 0.65. What is the CLINICAL implication of this difference?
30. Compound A is produced from sevoflurane reacting with the CO2 absorbent. At concentrations above 50–150 ppm, Compound A is nephrotoxic in rodents. What is the current clinical significance of this finding for sevoflurane use in humans?
31. The concentration effect and second gas effect are phenomena relevant to inhalational anaesthesia induction. Which statement BEST describes the second gas effect?
32. A 45-year-old patient undergoing elective laparoscopic cholecystectomy is maintained on sevoflurane. At sea level, the minimum alveolar concentration (MAC) of sevoflurane in an average 40-year-old adult is closest to:
33. A 60-year-old man with moderate hepatic dysfunction is scheduled for abdominal surgery. Which inhalational agent is MOST appropriate because it undergoes the least hepatic metabolism among the fluorinated agents?
34. During inhalational induction with sevoflurane in a closed-circuit system, compound A (fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether) is generated. The primary concern with Compound A is:
35. Nitrous oxide (N2O) is used as an adjunct during general anaesthesia. Which of the following accurately describes its mechanism of analgesic action?
36. A patient receiving N2O-based anaesthesia for a 4-hour bowel surgery develops postoperative megaloblastic changes. The underlying mechanism is:
37. Which of the following correctly describes the second gas effect and its clinical relevance when nitrous oxide is used alongside volatile agents?