MAC Does Not Matter to the Patient

Abstract

MAC Does Not Matter to the Patient To the Editor: We read with interest Dr Eger’s elegant paper elaborating on the effects of temperature and age on minimal alveolar concentration (MAC) of volatile anesthetics and nitrous oxide in humans (1). The concept of MAC, immobility and amnesia, is reproducible, easy to use, and requires minimal equipment. These main characteristics may be acceptable endpoints for the anesthesiologist and a convenient way of self-assurance. However, we would like to question the failure to withdraw to a painful stimulus (immobility) as a result of a change in temperature as this may easily represent a change of pain perception rather than an effect of the anesthetics in question. Further, immobility can be produced by a variety of drugs such a butyrophenones and opioids without a change in the level of consciousness. This withdrawal reflex becomes irrelevant once muscle relaxants are used. Patients undergoing a general anesthesia expect unconsciousness and would prefer not to rely on amnesia for this period. Understanding and eventually measuring unconsciousness must be the primary goal for anesthesiologists. Further adjustments of the MAC value for age, temperature and ambient pressure will improve our prediction of failure to withdraw to a painful stimulus but not that of unconsciousness. T. Engelhardt P.R. Lowe