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Inhalational anesthetics

Last updated: March 4, 2021

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Inhalational anesthetics are used for the induction and maintenance of general anesthesia as well as sedation. The exact mechanisms by which they act are still unknown. The most common inhalational anesthetics are sevoflurane, desflurane, and nitrous oxide. Of these, sevoflurane is the most common because of its rapid onset of action and the fact that patients recover quickly from it. Inhalational anesthetics cause respiratory depression, a decrease in arterial blood pressure and cerebral metabolic demand, and an increase in cerebral blood flow. While side effects differ based on the substance (e.g., halothane can cause hepatotoxicity), the most common side effect is nausea.

  • Inhalational anesthetics provide both analgesia and narcosis and can be used for induction and maintenance of general anesthesia.
  • The exact mechanism of action of inhalational anesthetics is still unknown.
  • The most widely used inhalational anesthetics are:
    • Nitrous oxide
    • Desflurane
    • Sevoflurane
    • Isoflurane
    • Enflurane (no longer marketed in the US)
    • Halothane (no longer marketed in the US)
    • Methoxyflurane

References:[1]

Pharmacokinetic principles

Pharmacodynamic principles

Pharmacokinetics and pharmacodynamics of common inhalational anesthetics

References:[1][2][3][4]

General effects

  • Anesthesia
  • Sedation/narcosis
  • ↓ Respiration
  • ↓ Arterial blood pressure
  • Myocardial depression
  • ↓ Cerebral metabolic demand
  • ↑ Cerebral blood flow
  • ↑ ICP
  • Postoperative: nausea and vomiting

Specific characteristics of common inhalational anesthetics

Specific characteristics
Nitrous oxide
  • Can cause expansion of gas trapped in a cavity
  • Usually insufficient if used alone → often combined with a more potent inhalational anesthetic to achieve the “second gas effect”
  • Rapid onset and recovery
Desflurane
  • Very rapid onset and recovery
  • Pungent odor; irritates airways → not suitable for induction of anesthesia
Sevoflurane
  • Most commonly used inhalational anesthetic
  • Rapid onset and recovery
  • Nonpungent → suitable for induction of anesthesia
Isoflurane
  • Most potent of the fluranes
  • Relatively slow onset and recovery
  • Pungent odor → not suitable for induction of anesthesia
Methoxyflurane
Enflurane
  • Seizures (proconvulsive)
  • Medium speed of onset and recovery
Halothane
  • Hepatotoxicity
  • Medium speed of onset and recovery

References:[1][2][3]

References:[1][3][5][6][8]

We list the most important adverse effects. The selection is not exhaustive.

  1. King A, Weavind LM, Joshi GP, Nussmeier NA. General Anesthesia: Induction. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/general-anesthesia-induction.Last updated: September 7, 2017. Accessed: September 25, 2017.
  2. Le T, Bhushan V. First Aid for the USMLE Step 1 2015. McGraw-Hill Education ; 2014
  3. Katzung B,Trevor A. Basic and Clinical Pharmacology. McGraw-Hill Education ; 2014
  4. ASA. Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: Application to healthy patients undergoing elective procedures. Anesthesiology. 2011; 114 (3): p.495-511. doi: 10.1097/aln.0b013e3181fcbfd9 . | Open in Read by QxMD
  5. Drug record - Halothane. https://livertox.nih.gov/Halothane.htm. . Accessed: October 6, 2017.
  6. Halothane Hepatotoxicity. http://emedicine.medscape.com/article/166232-overview. Updated: October 17, 2016. Accessed: October 12, 2017.
  7. Eger EI II . Characteristics of anesthetic agents used for induction and maintenance of general anesthesia. Am J Health Syst Pharm. 2004; 61 (20).
  8. Wenker OC. Review of Currently Used Inhalation Anesthetics; Part I. The Internet Journal of Anesthesiology. 1999; 2 (3).