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Isoflurane
Uses: Induction and maintenance of general anaesthesia.
Chemical: Halogenated methyl ether. Structural isomer of Enflurane.
Uses: Induction and maintenance of general anaesthesia.
Chemical: Halogenated methyl ether. Structural isomer of Enflurane.
Presentation: Clear colourless liquid, with a pungent smell.
Mode of action: Mechanism of general anaesthesia remains unclear.
Routes: Inhalation, via a calibrated vaporiser. Induction dose 1-4%, maintenance 0.5-3%.
Effects
Cardiovascular system: Mild negative inotrope, marked decrease in systemic vascular resistance thus leading to a decrease in mean arterial pressure. Causes a reflex tachycardia. Suggested to cause ‘coronary steal’. Coronary vasodilatation in the presence of fixed coronary arterial stenotic lesions may cause redistribution of blood from the endo- to the epicardium.
Respiratory system: Respiratory depressant. Decreases tidal volume, has little effect on respiratory rate. Decreased response to hypoxia and hypercapnia. Very irritant to respiratory tract. Causes bronchodilatation.
Central nervous system: Principal effect is general anaesthesia; little analgesic effect. Causes increased cerebral blood flow in concentrations >1 MAC.
Abdominal system: Maintains hepatic blood flow.
Genitourinary system: Tone of pregnant uterus is reduced.
Toxicity: Trigger agent for malignant hyperthermia. Isolated reports of hepatotoxicity.
Absorption: Coefficients - Blood/gas: 1.4, oil/gas: 98, MAC: 1.15
Distribution: Initially to areas of high blood flow (brain, heart, liver and kidney). Later to less well-perfused organs.
Metabolism: 0.2% of dose is slowly metabolised in the liver (oxidation/dehalogenation).
Excretion: Principally exhaled unchanged. 0.2% in urine as fluorinated compounds.
Special points: Potentiates action of non-depolarising muscle relaxants
[justify][center][left][center]Mode of action: Mechanism of general anaesthesia remains unclear.
Routes: Inhalation, via a calibrated vaporiser. Induction dose 1-4%, maintenance 0.5-3%.
Effects
Cardiovascular system: Mild negative inotrope, marked decrease in systemic vascular resistance thus leading to a decrease in mean arterial pressure. Causes a reflex tachycardia. Suggested to cause ‘coronary steal’. Coronary vasodilatation in the presence of fixed coronary arterial stenotic lesions may cause redistribution of blood from the endo- to the epicardium.
Respiratory system: Respiratory depressant. Decreases tidal volume, has little effect on respiratory rate. Decreased response to hypoxia and hypercapnia. Very irritant to respiratory tract. Causes bronchodilatation.
Central nervous system: Principal effect is general anaesthesia; little analgesic effect. Causes increased cerebral blood flow in concentrations >1 MAC.
Abdominal system: Maintains hepatic blood flow.
Genitourinary system: Tone of pregnant uterus is reduced.
Toxicity: Trigger agent for malignant hyperthermia. Isolated reports of hepatotoxicity.
Absorption: Coefficients - Blood/gas: 1.4, oil/gas: 98, MAC: 1.15
Distribution: Initially to areas of high blood flow (brain, heart, liver and kidney). Later to less well-perfused organs.
Metabolism: 0.2% of dose is slowly metabolised in the liver (oxidation/dehalogenation).
Excretion: Principally exhaled unchanged. 0.2% in urine as fluorinated compounds.
Special points: Potentiates action of non-depolarising muscle relaxants
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