II. Indications
- General Anesthetic Gas
III. Contraindications
- Malignant Hyperthermia Family History or personal history
IV. Definitions
- Ether
- Organic compounds in which two carbon atoms are linked through an oxygen atom (C-O-C)
- Diethyl ethers have historically been used as inhaled Anesthetics
V. Background
- Newer inhaled Anesthetics (Desflurane, Sevoflurane) are fully fluorinated analogs of Isoflurane
- Isoflurane (partially fluorinated) required a longer recovery period (esp. in obese patients) than these newer analogs
- These newer agents are also not flammable (contrast with Nitrous Oxide)
- Older agents (Halothane, Enflurane) are not in typical modern use in the U.S.
- These older agents were associated with a greater degree of myocardial depression and adverse effects
- First inhalation Anesthetic was ether
- Ether was synthesized in 1540, and was first used for medical Anesthesia in the U.S. in the 1840s
- Nitrous Oxide was also used during this time period, first used in 1772
- Chaturvedi (2011) Med J Armed Forces India 67(4):306-8 +PMID: 27365835 [PubMed]
VI. Mechanism
- Ethers with general Anesthetic (Sedative, hypnotic effects) and Skeletal Muscle Relaxant properties
- Most inhaled Anesthetics are fluorinated
- Inhalational agents are supplied as liquids and are vaporized to gas for inhalation
- CNS concentrations are directly related to alveolar concentrations
- Minimal alveolar concentration (MAC) reflects level at which 50% of patients will not move with painful stimulus
- Blocks release and re-uptake of Neurotransmitters at post-synaptic terminals and decreases conductance
- May affect Neuron ion channels and may also activate GABA Receptors
VII. Medications: Sevoflurane
- Minimum Alveolar Concentration: 1.8%
- Used in the U.S. since the 1990s and is among the most commonly used inhalational Anesthetics for surgery
- Safety
- Pregnancy Category C
- Unknown safety in Lactation
VIII. Medications: Desflurane
- Minimum Alveolar Concentration: 6.0%
- Safety
- Pregnancy Category B
- Considered safe in Lactation
- Precautions
- Laryngospasm is common (avoid in pediatrics)
- Avoid as sole Anesthetic in Coronary Artery Disease
IX. Medications: Isoflurane
X. Pharmacokinetics
- Isoflurane undergoes minimal metabolism (hence fewer adverse effects than Halothane or Enflurane)
- All volatile Anesthetics deposit in fatty tissue
XI. Adverse Effects
- Cardiovascular
- Myocardial Depression, decreased contractility and decreased mean arterial pressure
- Decreased Vascular resistance
- Myocardial Catecholamine sensitization
- Respiratory
- Respiratory depression
- Bronchodilation
- Other Serious Effects
- Malignant Hyperthermia (all volatile Anesthetics)
- Allergic Hepatotoxicity (Halothane)
- Enflurane (Nephrotoxicity)
- Diffuse Alveolar Hemorrhage (Sevoflurane)
XII. Resources
- Desflurane (DailyMed)
- Isoflurane (DailyMed)
- Sevoflurane (DailyMed)
XIII. References
- Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 56-7
- Smith (2023) General Anesthesia for Surgeons, StatPearls, Treasure Island, FL