MAC: factors affecting
Last updated: 03/05/2015
Factors affecting MAC:
- 1. Significant hypoxia (below 40 mm Hg) decreases MAC.
- 2. Hypothermia decreases MAC.
- 3. Hyperthermia increases MAC.
- 4. Hyperthyroidism slightly raises MAC (about 15%)
- 5. Increasing age decreases MAC
- Neonatal Halothane MAC: 1.1
- 70 y.o. MAC: 0.63
- 6. Circadian rhythms alter MAC + 10%
- 7. Opioids reduce MAC, but there is a ceiling effect beyond which additional opioid does not lower MAC.
- 8. Diazepam (and presumably other benzodiazepines) reduces MAC.
- 9. Scopolamine slightly lowers MAC.
- 10. Other volatile agents reduce MAC:
- MACs are additive: 50% N2O + .5MAC Halothane = 1 MAC of anesthetic
- 11. Drugs which reduce central catecholamines lower MAC:
- Alpha methyl dopa (Aldomet)
- chronic amphetamine use
- 12. Drugs which raise central catecholamines raise MAC
- acute amphetamine intoxication
- MAO inhibitors
- 13. Relaxants lower MAC slightly (but don’t push your luck!)
- 14. Pregnancy decreases MAC
- 15. Recently, it has been demonstrated that hair color effects MAC with red-haired people requiring about 20% more than others.
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