GasGasGas - Anaesthetic Science for Anaesthesia! MAC & Blood:Gas Coefficients: Volatile Anaesthetic Pharmacology
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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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.
Interpreting The Wash-In Curve
- The wash-in curve plots time versus FA/FI to show how quickly alveolar fraction approaches inspired fraction.
- FA/FI nears one only after prolonged equilibration and minimal losses to uptake or scavenging.