MAC by Age

CRNA Study Suite · Volatile Anesthetic Requirements
All Calculators MAC
Patient & Plan
Reference — MAC (40 yo)
AgentMAC*MAC w/ 60-70% N₂O
Sevoflurane2.0%0.66%
Desflurane6.0%2.38%
Isoflurane1.17%0.56%
Nitrous Oxide104%—
*Reference patient ages 30-60. (Nagelhout, 2023, p. 90)
Age-Adjusted MAC for Selected Agent
Base MAC (40 yo)
--
%
1.0 MAC (age-adjusted)
--
% et
MAC-Awake (0.33×)
--
%
MAC-BAR (1.85×)
--
%
Clinical Target (1.2 MAC)
--
%
Age-Adjustment
--
vs 40 yo baseline
Calculation Breakdown
Age Adjustment
MAC decreases ~6% per decade above 40 yr (Mapleson, 1996)
--
N₂O Adjustment (if selected)
N₂O 60-70% reduces MAC of potent agents by ~50%
--
(Nagelhout, 2023, p. 90)
MAC-Related Concepts
• MAC-Awake: ~0.3-0.4 × MAC — loss of recall
• MAC-BAR: 1.6-2.2 × MAC — blocks adrenergic response to incision
• Clinical target: ~1.2-1.3 MAC typical for maintenance
• Fentanyl 1.5 mcg/kg reduces desflurane MAC-BAR by ~85% (pre-incision)
(Nagelhout, 2023, pp. 90-91)
References

Nagelhout, J. J. (2023). Inhalation anesthetics. In S. Elisha, J. S. Heiner, & J. J. Nagelhout (Eds.), Nurse anesthesia (7th ed., pp. 87-100). Elsevier.

Mapleson, W. W. (1996). Effect of age on MAC in humans: A meta-analysis. British Journal of Anaesthesia, 76(2), 179-185. (Source of the "~6% per decade after 40" rule widely used clinically.)

How this works

What MAC means

Minimum alveolar concentration (MAC) is the alveolar concentration at which 50% of patients do not move in response to surgical incision, the standard measure of volatile potency. For patients age 30 to 60, MAC is 1.17% for isoflurane, 6.0% for desflurane, and 2.0% for sevoflurane; nitrous oxide requires 104% and cannot be used as a sole agent (Nagelhout, 2023, pp. 89-90).

How MAC changes with age

MAC declines with age, falling by roughly 6% per decade after age 40 for all volatile agents, so a 70 year old needs about 18% less anesthetic than a 40 year old (Ebert, 2024, p. 1346). MAC-awake, the concentration at which patients respond to command, is about one third to 0.4 times MAC; MAC-BAR, which blocks the adrenergic response to incision, is 1.6 to 2.2 times MAC (Nagelhout, 2023, pp. 90-91).

References

Nagelhout, J. J. (2023). Inhalation anesthetics. In Elisha, Heiner, & Nagelhout (Eds.), Nurse anesthesia (7th ed., pp. 87-100). Elsevier. Ebert, T. J. (2024). Inhaled anesthetics. In Barash, Cullen, and Stoelting's clinical anesthesia (9th ed.). Wolters Kluwer.