MAC (Minimum Alveolar Concentration) — the concentration at which 50% of patients don't move to a surgical incision

• Minimum Alveolar Concentration (MAC) is the end‑tidal alveolar concentration of an inhaled anesthetic that prevents movement in 50% of patients in response to a surgical (noxious) stimulus. It is the inhalational‑anesthetic equivalent of an ED₅₀ and is the standard measure of anesthetic potency. Wikipedia learnanesthesia.org droracle.ai

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  🧠 Core meaning (the one‑sentence takeaway)

  MAC quantifies how much inhaled anesthetic is needed to prevent movement in half of patients; lower MAC = more potent anesthetic. Wikipedia

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  🔍 What MAC actually measures

  • Population median effect — 50% do not move to incision at that concentration. Wikipedia
  • Measured at steady state (constant alveolar concentration for ~15 minutes). Wikipedia
  • Reflects spinal cord immobility, not amnesia or hypnosis (those occur at lower concentrations). droracle.ai

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  📏 Why anesthesiologists use MAC

  • Standardized potency comparison across volatile agents.
  • Real‑time dosing guide using end‑tidal anesthetic monitoring. medxdrg.com
  • Predictable physiologic behavior across species and conditions. Wikipedia

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  📉 MAC and potency

  • Lower MAC → more potent agent (requires less concentration).
    Example: Isoflurane (MAC ~1.17%) is more potent than Desflurane (MAC ~6.6%). learnanesthesia.org

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  📚 Important MAC derivatives

  • MAC‑awake (0.3–0.5 MAC): concentration at which patients regain awareness. Wikipedia
  • MAC‑BAR (1.7–2.0 MAC): blocks autonomic responses to painful stimuli. Wikipedia
  • MAC‑95 / MAC‑1.3: prevents movement in 95–99% of patients. learnanesthesia.org

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  📊 Typical MAC values (approximate, 40‑year‑old adult)

  Agent	MAC (%)
  Sevoflurane	1.8% learnanesthesia.org
  Isoflurane	1.17% learnanesthesia.org
  Desflurane	6.6% learnanesthesia.org

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  🧬 Factors that change MAC

  Decrease MAC (less anesthetic needed):

  • Increasing age
  • Hypothermia
  • Pregnancy
  • Hypotension
  • Opioids, α₂‑agonists (e.g., dexmedetomidine) Wikipedia
  • Nitrous oxide co‑administration (e.g., 60% N₂O reduces sevo MAC from 2.1% → ~1.4%) droracle.ai

  Increase MAC (more anesthetic needed):

  • Hyperthermia
  • Hypernatremia
  • Chronic alcohol use
  • Stimulant use learnanesthesia.org

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  🧩 Why MAC matters clinically

  • Helps titrate depth of anesthesia safely.
  • Predicts immobility but not memory suppression (which occurs at lower concentrations). droracle.ai
  • Allows additive calculation when combining agents (e.g., N₂O + volatile). learnanesthesia.org

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  Would you like next:

  • MAC‑awake vs MAC‑BAR explained
  • How age alters MAC values
  • Why volatile anesthetics differ in potency