What is MAC in anesthesia?

MAC (Minimum Alveolar Concentration) is the concentration of an inhaled anesthetic at 1 atmosphere that prevents movement in 50% of subjects in response to a standardized surgical skin incision. It is a measure of anesthetic potency — the lower the MAC, the more potent the agent.

How does age affect this estimate?

The calculator uses the published relationship MACage = MAC40 × 10^[-0.00269(age−40)] for ages at least one year. This is exponential, not a flat subtraction of 6% per decade.

What are the MAC values of sevoflurane, isoflurane and desflurane?

This tool uses the FDA label reference values: sevoflurane 2.1% at age 40, isoflurane 1.15% (label age band 31–55) and desflurane 6.0% (label mean age 45). With the age formula, sevoflurane MAC is about 2.38% at age 20 and 1.64% at age 80. These are population medians at 1 atm, not a dose for any individual.

Does one MAC mean the patient is unconscious?

No. MAC is based on movement after a noxious stimulus, not awareness, memory or adequate anesthesia for an individual. The tool intentionally does not generate MAC-awake or treatment targets.

How do you calculate total MAC with nitrous oxide?

MAC values of inhaled agents are approximately additive. Divide each end-tidal concentration by that agent's age-adjusted MAC and add the fractions. At age 40, 1.5% sevoflurane (1.5 ÷ 2.1 = 0.71 MAC) plus 50% N₂O (50 ÷ 104 = 0.48 MAC) gives about 1.20 MAC. At age 70 the same readings give about 1.44 MAC because both MACs are lower.

What is the MAC of nitrous oxide?

About 104% at age 40 in the Mapleson meta-analysis, so nitrous oxide alone cannot reach 1 MAC at normal atmospheric pressure. It is used as an adjunct: 50% end-tidal N₂O adds roughly 0.5 MAC in a middle-aged adult.

What factors increase or decrease MAC?

MAC is increased by hyperthermia, chronic alcohol use, and young age. MAC is decreased by hypothermia, opioids, benzodiazepines, age, pregnancy, hypotension, and acute alcohol intoxication.

Is this tool a substitute for clinical judgment?

No. This tool is an educational reference only. Clinical anesthetic management must be individualized and supervised by a qualified anesthesia provider. MAC values are population averages and do not account for all patient-specific factors.

MAC Anesthetic Helper

Age-adjusted MAC for five inhaled agents using MACage = MAC40 × 10^[-0.00269(age−40)], plus total MAC when a volatile agent is combined with nitrous oxide. Educational only, not medical advice or a dosing target.

Reference MAC at age 40 is 2.1% for sevoflurane, 1.15% for isoflurane, 6.0% for desflurane, 0.75% for halothane and 104% for nitrous oxide.

Not medical advice. Educational population reference only; it does not tell anyone what concentration to give.

Age-Adjusted MAC Calculator

Anesthetic Agent

Patient Age (years)

Validated calculator range: 1–100 years

Total MAC from end-tidal readings

MACs are approximately additive. Uses the age above and the volatile agent selected (N₂O is added separately).

Volatile ET (%)

N₂O ET (%)

Inhaled Anesthetic MAC Reference

Agent	MAC (40 yr)	Boiling Point (°C)	Notes
Sevoflurane	2.10%	58.5	FDA label reports 2.1% MAC at age 40.
Isoflurane	1.15%	48.5	FDA label age table reports 1.15% for ages 31–55.
Desflurane	6.00%	22.8	Label reports 6.0% at mean age 45; used as the adult reference.
Halothane	0.75%	50.2	0.75% at age 40 (Mapleson 1996); still used in some countries.
Nitrous oxide (N₂O)	104%	gas	104% at age 40 (Mapleson 1996): cannot reach 1 MAC alone at 1 atm.

Age-Adjusted MAC Table

MACage = MAC40 × 10^[−0.00269 × (age − 40)], 1 atm

Age	Factor	Sevo	Iso	Des	Halo	N₂O
1	1.273	2.67%	1.46%	7.64%	0.95%	132%
10	1.204	2.53%	1.38%	7.23%	0.90%	125%
20	1.132	2.38%	1.30%	6.79%	0.85%	118%
30	1.064	2.23%	1.22%	6.38%	0.80%	111%
40	1.000	2.10%	1.15%	6.00%	0.75%	104%
50	0.940	1.97%	1.08%	5.64%	0.70%	98%
60	0.883	1.86%	1.02%	5.30%	0.66%	92%
70	0.830	1.74%	0.95%	4.98%	0.62%	86%
80	0.781	1.64%	0.90%	4.68%	0.59%	81%
90	0.734	1.54%	0.84%	4.40%	0.55%	76%

Educational population estimate only, not medical advice. Do not use this output to select or change anesthetic concentration. MAC is a median (ED50) for no movement at skin incision; it does not measure awareness, memory, analgesia, hemodynamic tolerance, or adequacy of anesthesia for an individual. Opioids, sedatives, temperature, pregnancy and other factors shift MAC. Administration requires a qualified anesthesia professional and appropriate monitoring.

Quick answer

Reference MAC at age 40 is 2.1% for sevoflurane, 1.15% for isoflurane, 6.0% for desflurane, 0.75% for halothane and 104% for nitrous oxide. Age adjustment uses MACage = MAC40 × 10^[-0.00269 × (age − 40)], about 6% lower per decade. MACs add: total MAC = ET volatile ÷ its age MAC + ET N₂O ÷ N₂O age MAC. Educational population values, not medical advice.

Examples

Age (years)	Sevoflurane	Isoflurane	Desflurane	N₂O
1	2.67%	1.46%	7.64%	132%
20	2.38%	1.30%	6.79%	118%
40	2.10%	1.15%	6.00%	104%
60	1.86%	1.02%	5.30%	92%
80	1.64%	0.90%	4.68%	81%

Pick an agent and age to see the age-adjusted MAC, then add end-tidal values to get the total MAC with nitrous oxide.

Summary

Minimum alveolar concentration (MAC) is a population median: the alveolar concentration at 1 atmosphere that prevents movement in 50% of subjects after a standard surgical stimulus. This tool applies a published age relationship to labeled reference values; it does not prescribe concentration or measure consciousness.

How it works

Select an inhaled anesthetic agent from the list or view all agents in the comparison table.
Enter the patient age to calculate the age-adjusted MAC.
The tool applies MACage = MAC40 × 10^[-0.00269(age − 40)] for ages 1–100 years.
Review the exact multiplier and formula substitution.
Optionally enter end-tidal concentrations of the volatile agent and nitrous oxide: the tool adds each as a fraction of its own age-adjusted MAC (MACs are additive) to give total MAC.
Treat the output only as an educational population reference, never a dosing target.

Use cases

Teaching tool for anesthesia residents and students.
Comparing potency of different volatile anesthetic agents.
Understanding how a monitor's age-adjusted MAC readout combines a volatile agent with nitrous oxide.
Reproducing an age-adjusted MAC formula for coursework.

Frequently Asked Questions

Last updated: 2026-10-10 · Reviewed by Nham Vu