## Minimum Alveolar Concentration (MAC) Overview MAC is the alveolar concentration of an inhalational anesthetic at which 50% of patients do not move in response to a standard surgical incision. Lower MAC indicates greater potency. ### MAC Values of Common Inhalational Agents | Agent | MAC (%) | Potency | |-------|---------|----------| | Methoxyflurane | 0.16 | Highest | | Halothane | 0.75 | High | | Isoflurane | 1.15 | Moderate-high | | Sevoflurane | 2.0 | Moderate | | Desflurane | 6.0 | Lower | | Nitrous oxide | 104 | Lowest | **Key Point:** Methoxyflurane has the lowest MAC (0.16%), making it the most potent inhalational agent. However, it is rarely used clinically due to its nephrotoxicity from fluoride ion production. **High-Yield:** The relationship between MAC and potency is **inverse** — lower MAC = higher potency. Methoxyflurane's extremely low MAC reflects its high lipid solubility and blood-gas partition coefficient. **Clinical Pearl:** Nitrous oxide, despite being widely used, has an exceptionally high MAC (104%), which is why it cannot be used as a sole anesthetic agent and must be combined with other agents. **Mnemonic:** **MISH-DN** (in order of increasing MAC: **M**ethoxyflurane, **I**soflurane, **S**evoflurane, **H**alothane, **D**esflurane, **N**itrous oxide) — though this is a rough approximation and Halothane sits between Isoflurane and Methoxyflurane. ## Meyer-Overton Hypothesis The potency of inhalational agents correlates with their **lipid solubility**. Methoxyflurane's high lipid solubility explains its low MAC and high potency.
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