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Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane in man
1Department of Anaesthesia, City Hospital, Nottingham, UK. dicknickalls@compuserve.com
Background:
The motivation for this study was the current difficulty in estimating the total age-related MAC for a patient in a clinical setting.
Methods:
Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane were developed for the clinically useful MAC range (0.6-1.6), age range 5-95 yr, and put in a convenient form for use by practising anaesthetists. The charts are based on Mapleson's meta-analysis (1996) of the available MAC data and can be used to allow for the contribution of nitrous oxide to the total MAC.
Results:
The charts indicate the influence of age on anaesthetic requirements, showing, for example, that a total MAC of 1.2 using isoflurane and nitrous oxide 67% in oxygen requires an end-expired isoflurane concentration of only 0.25% in a patient of 95 yr vs 1% in a 5-yr-old patient. Colleagues found the charts to be helpful and simple to use clinically.
Conclusions:
The iso-MAC charts show clearly how patient age can be used to guide the choice of end-expired agent concentration. They also allow a consistent total MAC to be maintained when changing the inspired nitrous oxide concentration, thereby reducing the chance of inadvertent awareness, particularly at the extremes of age.
Insights
New charts simplify estimating age-related MAC for anesthetics like isoflurane. These tools help clinicians adjust anesthetic concentrations for patients of all ages, improving safety and reducing awareness risk.
Area of Science:
- Anesthesiology
- Pharmacology
Background:
- Clinical challenge in estimating age-related Minimum Alveolar Concentration (MAC).
- Need for practical tools for anesthesiologists.
Purpose of the Study:
- Develop age-related iso-MAC charts for common inhaled anesthetics.
- Provide a clinically applicable method for estimating anesthetic requirements.
Main Methods:
- Utilized Mapleson's 1996 meta-analysis of MAC data.
- Created charts for isoflurane, sevoflurane, and desflurane.
- Charts cover clinically relevant MAC (0.6-1.6) and age (5-95 years) ranges.
Main Results:
- Demonstrated significant influence of age on anesthetic requirements.
- Example: 95-year-old requires 0.25% end-expired isoflurane vs. 1% for a 5-year-old at a total MAC of 1.2 with 67% nitrous oxide.
- Charts found to be helpful and easy to use in clinical practice.
Conclusions:
- Iso-MAC charts effectively guide end-expired anesthetic agent concentration based on patient age.
- Facilitate consistent total MAC maintenance during changes in nitrous oxide concentration.
- Reduce the risk of inadvertent awareness, especially in elderly and pediatric patients.
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