MAC is a fundamental concept in anesthesiology that helps us understand and compare the potency of different inhalational anesthetics.
What is MAC?
MAC is defined as the minimum alveolar concentration of an inhaled anesthetic at 1 atmosphere pressure that prevents movement in 50% of patients in response to surgical incision.
Think of it as the ED50 (effective dose for 50% of the population) for inhaled anesthetics.
1.3 MAC is the concentration that is needed for 99% of patients to not move in response to a painful stimulus.
Clinical Application
- MAC 1.0 = The concentration needed for surgical anesthesia in average adult
- MAC 1.3 = Usually needed for more stimulating procedures
- MAC 0.3-0.5 = Often sufficient for sedation
Factors Affecting MAC
MAC requirements change based on patient factors:
- Decreases with:
- Increasing age
- Hypothermia
- Pregnancy
- Hypotension
- Increases with:
- Hyperthermia
- Chronic alcohol use
- Stimulant use
Common MAC Values
| Agent | MAC Value |
|---|---|
| Sevoflurane | 1.80% |
| Desflurane | 6.60% |
| Isoflurane | 1.17% |
Remember: The lower the MAC value, the more potent the agent!
Clinical Pearl
When using multiple anesthetic agents (like adding nitrous oxide or opioids), their effects are additive. This means you can use less of each agent while still achieving adequate anesthesia.
📚 References
1️⃣ Miller RD. Miller’s Anesthesia. 9th ed. Philadelphia, PA: Elsevier; 2020.
2️⃣ Morgan GE, Mikhail MS, Murray MJ. Morgan & Mikhail’s Clinical Anesthesiology. 6th ed. New York, NY: McGraw Hill; 2018.
3️⃣ Steiner J. Anesthesia Made Easy: The Survival Guide to Make Your First Anesthesia Rotation a Success. 2nd ed. Independently Published; 2019.
4️⃣ MAC Values of Commonly Used Inhaled Anesthetic Agents. ResearchGate. Available at: https://www.researchgate.net/figure/MAC-values-of-commonly-used-inhaled-anaesthetic-agents-10_tbl1_273040883.