Anaes · Volatile & inhalational agents
Isoflurane
Also known as 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether · Fluorinated methyl ether · Forane · Maintenance volatile agent · The workhorse volatile · Pungent volatile
Isoflurane is a fluorinated methyl ether volatile agent, the cheap stable maintenance volatile whose mild pungency makes mask induction slightly slower than halothane, with a MAC of 1.15 percent (1.5 times halothane, two-thirds enflurane), a blood-gas coefficient of 1.4, only 0.17 percent appearing as urinary metabolites (minimal hepato- or nephrotoxicity), the largest circulatory margin of safety with the least myocardial depression at a given MAC multiple but a dose-dependent fall in total peripheral resistance and arterial pressure with a heart-rate increase (Eger 1984). Its coronary-steal controversy (a 1983 vasodilator finding; steal demonstrated in a canine collateral model) was resolved by the early 1990s with no adverse cardiac changes under tightly controlled haemodynamics, and the work revealed a preconditioning cardioprotective effect (Crystal 2017; Buffington 1987; Bienengraeber 2005). Against desflurane it shows no optic-nerve-sheath-diameter difference with return to baseline (Rajmohan 2026, 50 analysed); prolonged ICU rescue sedation in difficult-to-sedate children reduces sedative burden but increases vasoactive support with frequent delirium and withdrawal (Biedermann 2026, 21 children); glial effects are dual with conflicting Alzheimer's-pathogenesis evidence (Wang 2026; Yang 2026); and theatre emissions are driven by agent choice, concentration and flow, nitrous oxide the largest contributor (Dogar 2026, 7231 cases).
Practise this topic
On this page
Study tools
Your progress
Saved on this device.
Target exams
Red flags
- Isoflurane IS a trigger of malignant hyperthermia — like every volatile agent, it must never be given to the known or suspected MH-susceptible patient; use a total intravenous technique with a vapour-free machine.
- Isoflurane is pungent and airway-irritant — it provokes coughing, breath-holding and laryngospasm in the awake patient and is NOT suitable for inhalational induction. Induction must be intravenous; isoflurane is a maintenance agent only.
- Isoflurane is a potent vasodilator that reduces systemic vascular resistance and mean arterial pressure; in hypovolaemia or shock the fall in blood pressure is exaggerated and the effective potency rises — titrate down or choose an intravenous technique.
- Isoflurane is a coronary vasodilator and was historically avoided in severe coronary disease for fear of coronary steal; the modern consensus is that steal is clinically insignificant in well-managed patients, but the concern is still examined and the haemodynamics must be controlled.
- Prolonged exposure in the developing brain produces neurotoxicity and apoptosis in preclinical models, and postoperative cognitive dysfunction in the elderly is debated; avoid prolonged high-dose exposure where alternatives exist, especially in neonates.
- Isoflurane is a greenhouse gas with a measurable global-warming potential and atmospheric lifetime; theatre scavenging is mandatory and the agent should be used at low fresh-gas flows to reduce both emissions and cost.
Meet the patient
A 65-year-old man with three-vessel coronary disease comes for major abdominal surgery. A junior suggests avoiding isoflurane "because of coronary steal". The consultant keeps isoflurane and explains that the steal controversy was resolved by the early 1990s — carefully performed studies showed no adverse cardiac changes as long as haemodynamic variables were tightly controlled — and that the controversy itself revealed isoflurane's preconditioning, cardioprotective effect.[7]
The two questions that frame isoflurane are: why is it maintenance? (mild pungency slows mask induction) and was the steal real? (demonstrated in a canine collateral model in 1987, resolved clinically by the early 1990s). Hold those, and the vasodilation, the preconditioning and the kinetics all follow.[6][7][8]
References9ShowHide
- [1]Biedermann R, et al. Isoflurane for difficult sedation in critically ill children: a retrospective analysis in a mixed pediatric intensive care population Front Pediatr, 2026.PMID 42290746
- [2]Yang L, et al. Inhaled General Anesthetics in Alzheimer's Disease Progression: Divergent Effects, Underlying Mechanisms, and Future Perspectives Mol Neurobiol, 2026.PMID 41915331
- [3]Wang X, Zhao M, Liu Z. The dual effects of anesthetics on glial cells: a review of neuroprotection and neurotoxicity Front Pharmacol, 2026.PMID 41669683
- [4]Dogar SA, et al. Anaesthetic gas emissions in a tertiary hospital in Pakistan: Behavioural drivers versus technological solutions J Clim Chang Health, 2026.PMID 42292653
- [5]Rajmohan N, et al. Comparison of the effects of isoflurane and desflurane on the optic nerve sheath diameter in elderly patients undergoing robotic-assisted laparoscopic radical prostatectomies in steep Trendelenburg position - A randomised controlled trial J Minim Access Surg, 2026.PMID 42085065
- [6]Eger EI 2nd. The pharmacology of isoflurane Br J Anaesth, 1984.PMID 6391530
- [7]Crystal GJ. Isoflurane and the Coronary Steal Controversy of the 1980s: Origin, Resolution, and Legacy J Anesth Hist, 2017.PMID 28641827
- [8]Buffington CW, et al. Isoflurane induces coronary steal in a canine model of chronic coronary occlusion Anesthesiology, 1987.PMID 3826685
- [9]Bienengraeber MW, et al. Cardioprotection by volatile anesthetics Vascul Pharmacol, 2005.PMID 15922257