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Inhalation anesthetic agents

Author
Stephen Robert Hays, MD, FAAP
Section Editor
Girish P Joshi, MB, BS, MD, FFARCSI
Deputy Editor
Nancy A Nussmeier, MD, FAHA

INTRODUCTION

This topic will review the mechanisms, pharmacokinetics, pharmacodynamics, advantages, disadvantages, and techniques employed to induce and maintain general anesthesia with inhalation anesthetics, including the potent volatile agents (sevoflurane, desflurane, isoflurane [and in some countries, halothane]) and one gas (nitrous oxide [N2O]). (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions".)

Intravenous agents used to induce and maintain general anesthesia are reviewed in separate topics. (See "General anesthesia: Intravenous induction agents" and "General anesthesia: Maintenance and emergence", section on 'Total intravenous anesthesia'.)

MECHANISMS OF ACTION

The precise mechanisms whereby inhalation agents induce general anesthesia are not known, and no single proposed mechanism of action fully explains their clinical effects (see 'Clinical effects' below). Various ion channels including gamma-aminobutyric acidA (GABAA), glycine, and glutamate receptors located in the central nervous system (ie, brain and spinal cord) are affected by the volatile inhalation anesthetics (sevoflurane, desflurane, and isoflurane) [1-4]. Nitrous oxide (N2O) gas is thought to act both by agonism of GABAA receptors and by antagonism of N-methyl-D-aspartate (NMDA) receptors [5,6].

Similarly, the mechanisms by which various intravenous agents are able to induce general anesthesia are not fully understood. (See "General anesthesia: Intravenous induction agents" and "General anesthesia: Maintenance and emergence", section on 'Total intravenous anesthesia'.)

PHARMACOKINETICS

General concepts — Inhalation agents are unique in their method of delivery via the lungs as a volume percent of inspired gas, rather than as a dose by weight with intravenous (IV) or oral medications. Inhalation agents are delivered via specialized airway circuits that are connected to an anesthesia machine, with scavenging of exhaled anesthetic gases to prevent environmental contamination of the operating room or interventional suite. Bottled volatile anesthetic liquids (sevoflurane, desflurane, isoflurane, halothane) are delivered via vaporizers on the anesthesia machine. Nitrous oxide (N2O) gas is supplied as a pressurized gas in equilibrium with its liquid phase in a cylinder, then delivered via a flow meter on the anesthesia machine (similar to delivery of other gases such as medical air or oxygen). (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions".)

                                                                    

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Literature review current through: Aug 2017. | This topic last updated: Sep 08, 2017.
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References
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