Isoflurane
Forane
Halogenated methyl ethyl ether — volatile anesthetic
Volatile anesthetic. Multiple sites: potentiates GABA-A, antagonizes NMDA, activates two-pore-domain K⁺ channels, modulates glycine. Lower potency than sevoflurane but produces deeper unconsciousness per MAC. Pungent — not used for inhalation induction.
Indications
- •Maintenance of general anesthesia
- •ICU sedation in long cases (less popular now; propofol or dexmedetomidine generally preferred)
- •Long surgical cases where slow emergence is acceptable and cost is a factor (cheapest of the three modern volatiles)
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| MAC | 1.15% (age 40); decreases ~6% per decade of age | — |
| Maintenance (1.0 MAC end-tidal) | 1.0–1.5% inspired | — |
Pharmacokinetics
Blood:gas partition coefficient 1.4 (slower than des [0.42] or sevo [0.65]). Slower onset and offset than the modern alternatives. Hepatic metabolism 0.2% (lowest of the three).
Hemodynamic effects
Dose-dependent ↓SVR > sevo > des; mild ↑HR; minimal contractility effect at <2 MAC. Coronary vasodilation more pronounced than other volatiles.
Respiratory effects
Pungent — coughing and laryngospasm on inhalation induction. Bronchodilator. Dose-dependent CO₂-response curve flattening.
Side effects
- !Pungency → coughing, breath-holding on induction (use only for maintenance)
- !Hypotension (greater SVR drop than sevo)
- !Tachycardia
- !Malignant hyperthermia trigger (any halogenated volatile)
- !Theoretical coronary steal in fixed CAD
Contraindications
- ×Known or suspected MH susceptibility
- ×Hypersensitivity
Clinical pearls
- ★CHEAPEST VOLATILE: per-MAC-hour cost ~1/3 of sevoflurane and ~1/5 of desflurane. Long cases at low fresh-gas-flow with careful CO2 monitoring make iso the budget winner.
- ★SLOW EMERGENCE: blood:gas coefficient 1.4 → 30–60 min wake-up after long maintenance. Not preferred for short cases.
- ★CORONARY STEAL: theoretical concern in patients with severe fixed multi-vessel CAD (Slogoff/Keats 1989); subsequent data soft. Most centers no longer treat this as a hard contraindication, but sevo is the cardiac-favored choice anyway.
- ★PEDIATRIC INDUCTION: too pungent for inhalation induction — sevoflurane is the only modern volatile suitable.
📊 Related teaching panels
Standalone diagrams matched to this topic.
Other drugs in Inhalation Agents
- Sevoflurane
Multi-site CNS depression: GABA-A potentiation, glycine receptor potentiation, NMDA + nicotinic ACh inhibition, two-pore K⁺ channel activation. Net: dose-dependent unconsciousness, amnesia, immobility, and analgesia (modest).
- Desflurane
Same multi-site mechanism as sevoflurane: GABA-A + glycine potentiation, NMDA + nicotinic ACh inhibition, K⁺ channel activation.
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