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Created: 6/4/2004


Uses: Induction and maintenance of general anaesthesia.

Chemical: Halogenated methyl ethyl ether. Structural isomer of isoflurane.


Presentation: Clear colourless liquid with a sweet smell (should be protected from light).

Mode of action: Mechanism of general anaesthesia remains unclear.

Routes: Inhalation, via a calibrated vaporiser. Induction dose 1-10%, maintenance 0.6-3%.


Cardiovascular system: Mild negative inotrope, marked decrease in systemic vascular resistance, thus leading to a decrease in mean arterial pressure. Causes a reflex tachycardia. Decreases coronary vascular resistance. Sensitises the myocardium to circulating catecholamines.

Respiratory system: Powerful respiratory depressant. Decreases tidal volume, although may increase respiratory rate. Decreased response to hypoxia and hypercapnia. Non-irritant to respiratory tract. Causes bronchodilatation. Inhibits pulmonary macrophage activity and mucociliary activity.

Central nervous system: Principal effect is general anaesthesia; little analgesic effect. Causes increased cerebral blood flow in concentrations >1 MAC. May induce tonic/clonic muscle activity and epileptiform EEG traces. Causes a marked decrease in skeletal muscle tone.

AS: Decreases splanchnic blood flow due to hypotension.

Genitourinary system: Decreases renal blood flow and glomerular filtration rate. Tone of pregnant uterus is reduced.

Toxicity: Trigger agent for malignant hyperthermia. Isolated reports of hepatotoxicity. Theoretical risk of fluoride ion toxicity in renal failure. May cause myocardial dysrhythmias.

Absorption: Coefficients: Blood/gas: 1.9, oil/gas: 98; minimal alveolar concentration: 1.68

Distribution: Initially to areas of high blood flow (brain, heart, liver and kidney). Later to less well-perfused organs.

Metabolism: 2.4% of dose is slowly metabolised in the liver (oxidation/dehalogenation). Plasma fluoride ion concentrations may reach 10 times those observed with halothane or isoflurane.

Excretion: More than 80% exhaled unchanged. 2.4% in urine as fluorinated compounds.

Special points: Potentiates action of non-depolarising muscle relaxants. Not recommended in epileptic patients.

Related examination questions

1. Enflurane:

(a) is a halogenated methyl-ethyl ether.
(b) has a blood/gas solubility coefficient of 1.43.
(c) lowers intracranial pressure.
(d) increases the tone of the pregnant uterus.
(e) causes a decrease in systemic vascular resistance.


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