Anaes · Volatile & inhalational agents
Volatile & inhalational agents
Also known as Inhalational agents · Volatile anaesthetics · Sevoflurane · Desflurane · Isoflurane · Minimum alveolar concentration
The volatile anaesthetic agents — sevoflurane, desflurane, isoflurane and the older halothane — together with xenon and nitrous oxide, produce general anaesthesia by an action on the central nervous system whose depth tracks the alveolar (and hence brain) partial pressure. The framework rests on four exam-critical ideas: potency correlates with lipid solubility (the Meyer-Overton correlation) and is measured by the minimum alveolar concentration (MAC); the speed of induction and emergence is governed by the blood:gas solubility (the lower the solubility, the faster); nitrous oxide is a special case — weak, analgesic, but one that expands closed gas spaces and inactivates vitamin B12; and every volatile is a trigger of malignant hyperthermia and an environmental greenhouse gas, considerations that increasingly shape the choice of agent. Built on the ENIGMA-II trial of nitrous-oxide safety (Myles 2014, Leslie 2015), the minimum-alveolar-concentration reviews (Sonner 2003, Eger 2001), halothane hepatitis (Ray 1991), the climate-impact assessment (Sulbaek Andersen 2023), the nephrotoxicity review (Hauquiert 2025), the EEG-guided emergence-delirium meta-analysis (Haidar 2026), the volatile-preconditioning review (Guerrero-Orriach 2022), and the inhalation-agent cardiovascular review (Hendrix 2025).
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- Every volatile anaesthetic is a trigger of malignant hyperthermia — never give a volatile (or succinylcholine) to the known or suspected MH-susceptible patient; use a total intravenous technique.
- Nitrous oxide expands closed gas spaces — it is contraindicated in pneumothorax, bowel obstruction, venous air embolism and middle-ear surgery, where the trapped gas expands and the pressure rises.
- Halothane sensitises the myocardium to catecholamines and causes immune-mediated halothane hepatitis — it has been largely abandoned; the modern agents (sevoflurane, desflurane, isoflurane) do not sensitise the myocardium and are not hepatotoxic in the same way.
- Desflurane is pungent and airway-irritant — it causes coughing, breath-holding and laryngospasm if used for inhalational induction; it is reserved for maintenance after the airway is secured.
- Several inhaled anaesthetics are potent greenhouse gases (desflurane taught as highest-impact); choose the lowest-impact agent that meets the clinical need and use low fresh-gas flows.
Meet the patient
A terrified five-year-old with no intravenous access needs a quick hernia repair. You pour sevoflurane into the circuit, hold the mask, and within a minute she is asleep — smooth, sweet-smelling, no needle. Five minutes after the surgeon finishes, she is awake and asking for her mother.[3]
That is the volatile agent doing what it does best: a non-pungent agent with moderate solubility that goes in fast and comes out fast, driven entirely by the alveolar partial pressure. Every exam question on volatiles comes back to that principle.[3]
References10ShowHide
- [1]Myles PS, Leslie K, Chan MT, Forbes A, et al. The safety of addition of nitrous oxide to general anaesthesia in at-risk patients having major non-cardiac surgery (ENIGMA-II): a randomised, single-blind trial Lancet, 2014.PMID 25142708
- [2]Leslie K, Myles PS, Kasza J, Forbes A, et al. Nitrous Oxide and Serious Long-term Morbidity and Mortality in the Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia (ENIGMA)-II Trial Anesthesiology, 2015.PMID 26501387
- [3]Sonner JM, Antognini JF, Dutton RC, Flood P, et al. Inhaled anesthetics and immobility: mechanisms, mysteries, and minimum alveolar anesthetic concentration Anesth Analg, 2003.PMID 12933393
- [4]Eger EI 2nd. Age, minimum alveolar anesthetic concentration, and minimum alveolar anesthetic concentration-awake Anesth Analg, 2001.PMID 11574362
- [5]Ray DC, Drummond GB. Halothane hepatitis Br J Anaesth, 1991.PMID 1859766
- [6]Sulbaek Andersen MP, Nielsen OJ, Sherman JD. Assessing the potential climate impact of anaesthetic gases Lancet Planet Health, 2023.PMID 37438003
- [7]Hauquiert B, Gonze A, Gennart T, Perriens E. Nephrotoxicity and Modern Volatile Anesthetics: A Narrative Review Toxics, 2025.PMID 40559988
- [8]Haidar L, Abadi F, Sarieddine T, Vitali A, et al. EEG-Guided Anesthesia for the Prevention of Emergence Delirium in Children: A Systematic Review and Meta-Analysis JAMA Pediatr, 2026.PMID 41627803
- [9]Guerrero-Orriach JL, Carmona-Luque MD, Gonzalez-Alvarez L, et al. Heart Failure after Cardiac Surgery: The Role of Halogenated Agents, Myocardial Conditioning and Oxidative Stress Int J Mol Sci, 2022.PMID 35163284
- [10]Hendrix JM, Kramer J. Anesthesia Inhalation Agents and Their Cardiovascular Effects StatPearls, 2025.PMID 31082134