Another type of non-volatile inhalation anesthetic that may eventually come into more regular use is xenon. Currently, xenon is more expensive to use than other inhalation anesthetics, and this has limited its use somewhat. However, xenon is an attractive prospect, as it is around 50% more potent than nitrous oxide, and as it is not a greenhouse gas, is also more environmentally-friendly.

Mode of Action

Inhalation anesthetics are administered via an anesthetic machine that uses a vaporizer to generate an inhalable gas from a liquid version of the anesthetic. Once inhaled, the gas is distributed throughout the body via the bloodstream at a rate that is dependent on the dose administered, the type of anesthetic used, and on more specific factors that depend on the patient who is receiving the anesthetic.

Inhalation anesthetics generally operate via one of two methods: increase of inhibitory function, or decrease of excitatory transmission, at brain nerve endings. In ideal situations, inhalation anesthetics induce anesthesia quickly, and emergence from the anesthetized state is rapid once the anesthetic stimulus is removed.

The body deals with inhalation anesthetics in two ways: via metabolism, and via exhalation. The ideal inhalation anesthetics are those which are metabolized only at low levels. Metabolism rates vary widely between different anesthetics: halothane, for example, is metabolized at a rate of 10% to 20%, while enflurane has a metabolism rate of around 2.5%, and nitrous oxide has a rate of 0%, and is not metabolized at all.

During a surgical procedure, inhalation anesthetics tend to accumulate in fatty tissue, meaning that patients with higher percentages of body fat will awaken from the anesthetized state slower than patients with less body fat.

Possible Side Effects and Toxic Effects

Most inhalation anesthetics produce a variety of different side effects. Some side effects occur only in one or two different anesthetics, while other side effects are common to almost all. Some of the most common side effects include the following:

Cardiovascular effects include decreased blood pressure (in all inhalation anesthetics except for nitrous oxide, and increased heart rate (isoflurane and halothane).

Pulmonary effects include an increase in respiratory rate. This increase is dose-dependent and is common to all inhalation anesthetics.

Renal and hepatic function is decreased following administration of all inhalation anesthetics. In extremely rare cases (between one in 6,000 and one in 35,000), necrosis of the liver may result from administration of halothane. Kidney toxicity, once a relatively common result of the use methoxyflurane, is occasionally seen following the administration of high doses of sevoflurane.

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