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Inhalational anesthetics

Last updated: September 21, 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.

Overview of inhalational anesthetics
Agents Indications Mechanism of action Adverse effects
Nitrous oxide
  • Exact mechanism of action still unknown, leads to:
    • Sedation/narcosis
    • Anesthesia (nitrous oxide)
    • ↓ Respiration and arterial blood pressure, myocardial depression
    • ↑ Cerebral blood flow and ICP, ↓ cerebral metabolic demand
  • PONV
  • Risk of malignant hypertherma
  • Can diffuse into gas-filled body compartments → expansion of the gas in that compartment
  • ↑ Pulmonary vessel resistance
Desflurane
Sevoflurane
  • Agitation (especially in pediatric patients) [1]
Isoflurane
Enflurane
  • Proconvulsive
Halothane
Methoxyflurane

Pharmacokinetic principles

Pharmacodynamic principles

Pharmacokinetics and pharmacodynamics of common inhalational anesthetics

References:[3][4][5][6]

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

References:[3][4][5]

General side effects

Side effects of specific substances

References:[4][5][7][8][10]

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

  1. ULTANE® (sevoflurane) volatile liquid for inhalation.
  2. FORANE (isoflurane, USP) Liquid For Inhalation.
  3. Le T, Bhushan V. First Aid for the USMLE Step 1 2015. McGraw-Hill Education ; 2014
  4. Katzung B,Trevor A. Basic and Clinical Pharmacology. McGraw-Hill Education ; 2014
  5. 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.
  6. 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
  7. Drug record - Halothane. https://livertox.nih.gov/Halothane.htm. . Accessed: October 6, 2017.
  8. Halothane Hepatotoxicity. http://emedicine.medscape.com/article/166232-overview. Updated: October 17, 2016. Accessed: October 12, 2017.
  9. Eger EI II . Characteristics of anesthetic agents used for induction and maintenance of general anesthesia. Am J Health Syst Pharm. 2004; 61 (20).
  10. Wenker OC. Review of Currently Used Inhalation Anesthetics; Part I. The Internet Journal of Anesthesiology. 1999; 2 (3).