Inhalation Agents

  • ​Solubility
  • Expressed as blood:gas partition coefficient
  • The higher the solubility of an agent, the longer it takes to acheive equilibrium. For example, Isoflurane B:G coefficient is 1.4 as compared to 0.65 of Sevofliurane. Therefore, it will take longer for isoflurane to acheive equiibrium.
  • Second Gas Effect- Commonly used term for use of Nitrous Oxide to assist faster onset of secondary agent such as sevoflurane. High volume of N20 increases the partial pressure of sevoflurane. 

  •  Agent Structure-
    • ​Sevoflurane- 7 Fluorine atoms. 
    • Desflurane- 6 Fluorine atoms. Similar to Isoflurane except has Fluorine atom instead of Isoflurane's chlorine atom.
    • Isoflurane- 5 Fluorine atoms and a chlorine atom. Chemical isomer of enflurane. Similar structure to desflurane.  
  • Nitrous Oxide
    • MAC- 105%
    • Gas at room temperature 
    • Increases CBF & CBV leading to mild increase in ICP
    • Increases CMro2
    • Decreases renal blood flow​.
Factors influencing MAC

Decrease- Hypothermia, Hyperthermia, Increase Age, Acute ETOH, Anemia, Opioids, Ketamine, Benzodiazepines, Alpha 2
                    Agonists, Chronic Amphetamine Use, Pregnancy, Hyponatremia, Hypercalcemia

Increase-  Young age, Chronic ETOH, Hypernatremia, Acute Amphetamine, Cocaine, Ephedrine. 

Morgan, G. Edward., et al. Clinical Anesthesiology. 4th ed., Lange Medical Books/McGraw Hill Medical Pub. Division, 2006.