Editorial Views  |   November 2017
MAC Meeting MIGET: Leaps of Faith
Author Notes
  • From the Department of Anesthesiology, Intensive Care and Pain Therapy, OLV Hospital, Aalst, Belgium (J.F.A.H.); Perioperative and Pain Medicine Unit, Melbourne Medical School, University of Melbourne, Melbourne, Victoria, Australia (P.J.P.); Department of Anesthesiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois (A.M.D.W.).
  • Corresponding article on page 800.
    Corresponding article on page 800.×
  • Accepted for publication July 21, 2017.
    Accepted for publication July 21, 2017.×
  • Address correspondence to Dr. Hendrickx: jcnwahendrickx@yahoo.com
Article Information
Editorial Views / Pharmacology
Editorial Views   |   November 2017
MAC Meeting MIGET: Leaps of Faith
Anesthesiology 11 2017, Vol.127, 741-743. doi:10.1097/ALN.0000000000001848
Anesthesiology 11 2017, Vol.127, 741-743. doi:10.1097/ALN.0000000000001848
WE don’t know whether Ted Eger, Larry Saidman, Bob Stoelting, Peter Wagner, and Göran Hedenstierna joined for dinner recently, but the article by Kretzschmar et al.1  in this issue of Anesthesiology might very well have been the result of misters MAC (minimal alveolar concentration)2–4  and misters MIGET (multiple inert gas elimination technique)5,6  getting together. The former three developed the MAC and MAC-awake concepts, reflecting the probability of immobility in the presence of a nociceptive stimulus and response to verbal command, respectively, when using inhaled anesthetics to provide general anesthesia, whereas the latter two used inhaled agents as some of the components of MIGET to determine the distribution of ventilation/perfusion ratios () in the lungs. MAC is based on end-expired agent partial pressures measurements at steady state. However, in discussions of uptake and distribution, Alveolar–arterial (A-a) partial pressure gradients are often glibly passed over and considered to be insignificant. On the other hand, MIGET determines scatter based on simultaneous end-expired and arterial blood agent partial pressure measurements of six inert gases after intravenous infusion.5  The underlying basis is that the wide differences in solubility of these six gases cause them to be washed out differently by areas with differing ratios, resulting in widely divergent A-a differences. Some of these gases are inhaled anesthetics (usually cyclopropane, halothane, and ether). So, on the one hand we like to assume that A-a gradients of inhaled anesthetics are small or nonexistent, but on the other hand, we use these same inhaled agents to study scatter based on A-a gradients! The work by Kretzschmar et al.1  is the first in which MIGET is used to help elucidate the finer aspects of anesthetic agent uptake. The authors determined in an animal model how methacholine-induced mismatching (assessed by MIGET) affects agent uptake of two clinically used agents with different blood–gas partition coefficients, isoflurane and desflurane. They are to be commended for this approach, but some aspects relating to methodology have to be scrutinized.
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