indication

Used for the induction and maintenance of general anaesthesia during surgery and cesarean section and also used for analgesia during vaginal delivery.

pharmacology

Enflurane is an extremely stable halogenated ether inhalation anesthetic that allows rapid adjustments of anesthesia depth with little change in pulse or respiratory rate. Enflurane induces muscle relaxation and reduces pains sensitivity by altering tissue excitability. Induction of and recovery from anesthesia with enflurane are rapid. Enflurane may provide a mild stimulus to salivation or tracheobronchial secretions. Pharyngeal and laryngeal reflexes are readily obtunded. In the cardiovascular system, enflurane is a mild negative inotrope, causing a marked decrease in systemic vascular resistance, thus leading to a decrease in mean arterial pressure. This results in a reflex tachycardia. Enflurane also decreases coronary vascular resistance and sensitizes the myocardium to circulating catecholamines. Enflurane is a strong respiratory depressant. It decreases tidal volume but may increase respiratory rate. It also causes bronchodilatationa and inhibits pulmonary macrophage activity and mucociliary activity. Enflurane principle action in the CNS is general anaesthesia with little analgesic effect. It causes increased cerebral blood flow in concentrations and may induce tonic/clonic muscle activity and epileptiform EEG traces. It also causes a marked decrease in skeletal muscle tone. Actions in the genitourinary system include a decreased renal blood flow and glomerular filtration rate and the tone of pregnant uterus is decreased.

mechanism of action

Enflurane induces a reduction in junctional conductance by decreasing gap junction channel opening times and increasing gap junction channel closing times. Enflurane also activates calcium dependent ATPase in the sarcoplasmic reticulum by increasing the fluidity of the lipid membrane. It also appears to bind the D subunit of ATP synthase and NADH dehydogenase. Enflurane also binds to and angonizes the GABA receptor, the large conductance Ca²⁺ activated potassium channel, the glycine receptor, and antagonizes the glutamate receptor receptor. These yield a decreased depolarization and therefore, tissue excitability which results in anesthesia.

toxicity

LD₅₀=5.4 ml/kg (oral, rat). Symptoms of acute overdose include nausea, vomiting, irritation to the eyes, skin and nose/throat, headache, dizziness, and drowsiness. Symptoms of chronic overdose include hypotension, cardiac arrhythmias, respiratory depression, and liver/kidney dysfunction.

biotransformation

2.4% of the dose is slowly metabolized hepatically via oxidation and dehalogenation (primarily through the actions of cytochrome P450 2E1). Leads to low levels of serum fluoride (15 µmol/L).

absorption

Rapidly absorbed into the circulation via the lungs.