MAC 3 - MAC in Practice

This is the third tutorial on MAC and in it I explore how MAC is and should be used in clinical practice. @ccmtutorials In this tutorial, we move beyond definitions of MAC (Minimum Alveolar Concentration) and explore how it is actually applied in everyday anesthesia practice. We clarify a critical concept: MAC is not a measure of depth of anesthesia, but rather a population-based estimate of anesthetic potency for immobility—primarily mediated at the spinal cord, not the brain. We examine how MAC should be used as a clinical target, and why it must always be interpreted in context. Key physiological modifiers of MAC are reviewed, including age (±6% per decade), pregnancy, temperature, metabolic state, and pharmacologic influences such as opioids, sedatives, and adrenergic drugs. The tutorial highlights the steep, sigmoidal dose–response relationship of volatile anesthetics, emphasizing how small changes in concentration produce large clinical effects. We also explore important concepts such as hysteresis (neural inertia) during induction and emergence, and how this affects anesthetic requirements over time. A major focus is the transition from IV induction (propofol) to inhalational maintenance, including the use of overpressure (≈2 MAC) and the importance of timely reduction in vaporizer settings to avoid overshoot and hypotension. We then integrate MAC into modern balanced anesthesia, demonstrating how opioids, multimodal analgesia, and neuromuscular blockade significantly reduce volatile requirements—often to well below 1 MAC during maintenance. Practical guidance is provided on safe targets (typically ≥0.7 MAC to minimize awareness risk) and how to adjust anesthetic delivery throughout the phases of surgery. Finally, we address a common and important issue: anchoring bias, where clinicians fixate on “1 MAC” and risk overdosing—particularly in older patients. Description 00:03 Introduction 01:37 MAC is NOT Adequate Depth of Anesthesia 04:06 What Changes MAC - Factors that Increase MAC 05:08 What Deceases MAC 05:58 MAC is Reduced in Pregnancy 06:33 MAC and Dose Responsiveness 09:02 The Hill Co-Efficient 09:53 Propofol vs Sevoflurane 11:00 Anesthesia Transition and MAC 12:32 Overpressure 13:35 Age Adjustment 15:43 Dose Adjustment During Surgery 16:22 Hysteresis 18:25 MAC in the Real World (example on how to use MAC during surgery) 20:48 End Tidal Goal During Surgery (never less than 0.7 Age Adjusted MAC) 21:20 A Suggested Strategy During Standard General Anesthesia for Utilizing MAC 23:42 Where Does MAC-BAR Stand in the era of "Balanced Anesthesia" 24:24 Anchoring Bias 25:51 Why We Still Use MAC 26:18 Review