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TCI Marsh vs Schnider Models — FRCA Final MCQ

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HardGeneral AnaesthesiaTCI Marsh vs Schnider ModelsFRCA Final

A patient on TCI propofol (Marsh model) has measured blood concentration 30% higher than predicted effect-site concentration during maintenance. What is the most likely explanation?

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Correct answer: D — The Marsh model does not include an effect-site compartment

The Marsh model targets plasma concentration and does not incorporate an effect-site (Ce) compartment. During maintenance, measured blood exceeds predicted Ce because of the plasma-effect-site equilibration delay (ke0). The Schnider model incorporates effect-site targeting. This is expected pharmacokinetic behaviour.

Reference: RCOA – 2020 – Primary curriculum: Pharmacokinetics of IV anaesthetic agents