GasGasGas - The FRCA Primary Exam Podcast Gas Gas Gas - MAC and the Partition Coefficients
Nov 3, 2024
Dive into the fascinating world of volatile anesthetics as the discussion unfolds around Minimum Alveolar Concentration (MAC). Learn how age and effect sites influence MAC, and why end-tidal concentrations matter. Explore the different MAC values for sevoflurane and halothane, alongside insights into the wash-in curve. Delve into the blood-gas coefficient's impact on onset and recovery, and uncover how opioids modify MAC responses. Plus, the implications of MAC-amnesia and thresholds for airway procedures make for a riveting listen!
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What MAC 1 Actually Means
- MAC 1 means the end-tidal volatile concentration that prevents movement in 50% of patients during a standard incision.
- This measurement assumes no IV induction, no muscle relaxants, and no opiates on board.
MAC Changes With Age
- MAC decreases with age; younger patients need more agent and older patients need less.
- The change is roughly 6% per decade of age.
Why End-Tidal Matters
- We use end-tidal concentration as a surrogate for alveolar concentration, which approximates brain effect-site concentration at equilibrium.
- End-tidal is measured at the end of expiration to avoid dead-space gas misleading the value.