Volatile Agent Uptake and Cardiac Output — FRCA Final MCQ

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HardGeneral AnaesthesiaVolatile Agent Uptake and Cardiac OutputFRCA Final

A 45-year-old woman (ASA II, 65 kg) undergoes a laparoscopic hysterectomy. During surgery she develops an increasing end-tidal sevoflurane concentration without any change in the vaporiser setting, and the inspiratory sevoflurane concentration also rises. What is the most likely explanation?

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Correct answer: D — Reduced cardiac output causing reduced uptake of volatile agent

When cardiac output falls (e.g., from haemorrhage, myocardial depression, or high pneumoperitoneum pressure), less volatile agent is carried away from the alveoli by the pulmonary blood flow. This results in higher alveolar (end-tidal) concentrations of volatile agent for the same delivered concentration – a positive feedback that can deepen anaesthesia and further reduce cardiac output. The rising inspiratory concentration suggests accumulation in the circle system due to reduced uptake. This is an important physiological principle in volatile agent pharmacokinetics.

Reference: RCOA – 2023 – Final FRCA curriculum: uptake and distribution of volatile agents; Eger EI – 1974 – Anaesthetic uptake and action