• Clinical science

Inhalational anesthetics (Volatile anesthetics)


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:


Pharmacokinetics and pharmacodynamics

Pharmacokinetic principles

  • Uptake into the blood: inhalational anesthetics are taken up passively via diffusion, which depends on:
  • Distribution and uptake into the brain: Transport to and uptake into the brain depend on cerebral perfusion and the fat solubility of the inhalational anesthetic.
  • Onset of effect: : The lower the blood-gas partition coefficient of an inhalational anesthetic, the faster the substance takes effect (less induction time)
  • Elimination
    • Inhalational anesthetics are eliminated by the lungs
    • Inhalational anesthetics are metabolized only to a small degree
    • With prolonged duration of anesthesia in obese patients, inhalational anesthetics with a high fat solubility can accumulate in adipose tissue and slow down recovery from anesthesia (increased context-sensitive half-life).

Pharmacodynamic principles

  • Measure of potency of inhalational anesthetics: minimal alveolar concentration (MAC)
    • MAC is the fraction of volume of the anesthetic present in the inspired air that provides sufficient analgesia in 50% of patients, meaning that patients will not respond to an extremely painful stimulus such as surgical skin incision.
    • MAC is inversely related to anesthetic potency (potency = 1/MAC) and represents the ED50 value.
    • The lower the MAC value, the more fat soluble the anesthetic. For example:
      • Halothane has a slow induction and high potency because of its high lipid and blood solubility.
      • Nitrous oxide (N2O), in contrast, has a fast induction and low potency due to low lipid and blood solubility.

Pharmacokinetics and pharmacodynamics of common inhalational anesthetics

Blood-gas partition coefficient Brain-blood partition coefficient Minimal alveolar concentration (MAC)
Nitrous oxide
  • 0.47
  • 1.1
  • > 104%
  • 0.42
  • 1.3
  • 6–7%
  • 0.69
  • 1.7
  • 2%
  • 1.40
  • 2.6
  • 1.4%
  • 1.80
  • 1.4
  • 1.7%
  • 2.30
  • 2.9
  • 0.75%



General effects

  • Anesthesia
  • Sedation/narcosis
  • ↓ Respiration
  • ↓ Arterial blood pressure
  • Myocardial depression
  • ↓ Cerebral metabolic demand
  • ↑ Cerebral blood flow
  • 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
  • Very rapid onset and recovery
  • Pungent odor; irritates airways → not suitable for induction of anesthesia
  • Most commonly used inhalational anesthetic
  • Rapid onset and recovery
  • Nonpungent → suitable for induction of anesthesia
  • Most potent of the fluranes
  • Relatively slow onset and recovery
  • Pungent odor → not suitable for induction of anesthesia
  • Seizures (proconvulsive)
  • Medium speed of onset and recovery
  • Hepatotoxicity
  • Medium speed of onset and recovery


Adverse effects


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

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last updated 11/18/2020
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