Isoflurane is a halogenated volatile inhalation anesthetic agent, widely used for the induction and maintenance of general anesthesia. It is a structural isomer of enflurane. It provides rapid induction and recovery due to its low blood-gas solubility coefficient (1.4). It is a potent anesthetic with a Minimum Alveolar Concentration (MAC) of approximately 1.15% in adults. It provides good muscle relaxation and is relatively stable, with only about 0.2% metabolized in the body.
Adult: Induction: 1.5-3.0% (with oxygen/nitrous oxide). Maintenance: 1.0-2.5% (with oxygen/nitrous oxide). For ICU sedation: 0.1-0.6%. Dosage must be individualized based on patient response, use of premedication, and concurrent agents. MAC decreases with age, hypothermia, and concomitant use of other CNS depressants.
Note: Administered ONLY via a calibrated, agent-specific vaporizer in an anesthesia delivery system. Must be used with adequate oxygenation. Always ensure proper scavenging of waste gases. Premedication with sedatives/opioids is common. Neuromuscular blocking agents are used adjunctively. Monitor vital signs (ECG, BP, SpO2, EtCO2, temperature) continuously.
Isoflurane produces a reversible depression of the central nervous system, leading to loss of consciousness, amnesia, and immobility. Its exact mechanism is complex and multifactorial, primarily involving potentiation of inhibitory neurotransmission (GABA-A, glycine receptors) and inhibition of excitatory neurotransmission (NMDA receptors). It also modulates various ion channels (e.g., two-pore domain potassium channels).
Pregnancy: Category C (US FDA). Can be used for maintenance of anesthesia during caesarean delivery. May cause dose-related depression in the newborn. Not recommended for use during first trimester unless absolutely necessary. Uterine relaxation and potential for increased blood loss may occur.
Driving: Patients must be advised not to drive, operate machinery, or make important decisions for at least 24 hours after general anesthesia due to residual CNS effects and co-administered medications.
| Non-depolarizing Muscle Relaxants (e.g., Atracurium, Vecuronium) | Potentiates neuromuscular blockade, reducing required dose. | Major |
| Succinylcholine | May increase risk of malignant hyperthermia and hyperkalemia. | Major |
| Opioid Analgesics (e.g., Fentanyl, Morphine) | Additive CNS, respiratory, and cardiovascular depression. | Major |
| Benzodiazepines (e.g., Midazolam) | Additive CNS depression, reduces MAC requirement. | Moderate |
| Beta-blockers (e.g., Propranolol) | Additive myocardial depression and bradycardia. | Moderate |
| Calcium Channel Blockers (e.g., Verapamil) | Enhanced negative inotropic and chronotropic effects. | Moderate |
| Aminoglycoside Antibiotics (e.g., Gentamicin) | May enhance neuromuscular blockade. | Moderate |
| Theophylline | May lower seizure threshold; potential for arrhythmias. | Moderate |
Same composition (Isoflurane (NA)), different brands: