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Are estimates of MAC reliable?

M Paul1, D M Fisher

  • 1Department of Anesthesia, University of California, San Francisco, USA.

Anesthesiology
|December 19, 2001
PubMed
Abstract

Insights

Estimating anesthetic potency (minimum alveolar concentration [MAC]) can be inaccurate due to study design. Increasing the number of patient crossovers improves accuracy, but benefits plateau after six crossovers.

Area of Science:

  • Anesthesiology
  • Pharmacology
  • Statistical Modeling

Background:

  • Minimum alveolar concentration (MAC) is a measure of inhaled anesthetic potency.
  • Traditional MAC studies use an up-down method, assessing only one quantal response per patient.
  • This limits the determination of individual MAC values and introduces potential inaccuracies.

Purpose of the Study:

  • To evaluate the impact of interindividual variability on MAC estimates.
  • To assess how study design factors influence the accuracy of MAC estimations.
  • To identify optimal parameters for reliable MAC determination.

Main Methods:

  • Simulated the standard up-down MAC study protocol.
  • Varied key factors: starting concentration, number of crossovers, concentration increment, interindividual variability, and measurement error.
  • Replicated simulations 500 times for each factor to analyze estimate accuracy and variability.

Main Results:

  • Starting concentrations near the true MAC minimized variability underestimation.
  • More than six crossovers minimally improved MAC estimates but increased variability estimates.
  • Larger increment sizes and higher interindividual variability led to more outlier MAC estimates.
  • Many simulations resulted in MAC estimates deviating over 10% or 25% from the true value.

Conclusions:

  • Individual MAC experiments can produce inaccurate potency estimates.
  • Increasing patient crossovers enhances accuracy, with diminishing returns beyond six.
  • Study design significantly impacts the reliability of MAC measurements.

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