Drug information of Enflurane

Enflurane

Drug group:

An extremely stable inhalation anesthetic that allows rapid adjustments of anesthesia depth with little change in pulse or respiratory rate.

Mechanism of effect

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.

Pharmacodynamic

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.

Pharmacokinetics

Rapidly absorbed into the circulation via the lungs. Volume of distributio is not Available. Protein binding is 97%. 2.4% of the dose is slowly metabolized hepatically via oxidation and dehalogenation (primarily through the actions of cytochrome P450 2E1). Route of elimination is not Available. Half life is not Available too.

Dosage

Surgical Anesthesia

Induction may be achieved using Enflurane alone with oxygen or in combination with oxygen-nitrous oxide mixtures. Under these conditions some excitement may be encountered. If excitement is to be avoided, a hypnotic dose of a short-acting barbiturate should be used to induce unconsciousness, followed by the Enflurane mixture. In general, inspired concentrations of 2.0 to 4.5% Enflurane produced surgical anesthesia in 7 to 10 minutes.

Maintenance

Surgical levels of anesthesia may be maintained with 0.5 to 3% Enflurane Maintenance concentrations should not exceed 3%. If added relaxation is required supplemental doses of muscle relaxants may be used. Ventilation to maintain the tension of carbon dioxide in arterial blood in the 35 to 45 mm Hg range is preferred. Hyperventilation should be avoided in order to minimize possible CNS excitation.

The level of blood pressure during maintenance is an inverse function of Enflurane concentration in the absence of other complicating problems. Excessive decreases (unless related to hypovolemia) may be due to depth of anesthesia and in such instances should be corrected by lightening the level of anesthesia.

Analgesia

Enflurane 0.25 to 1% provides analgesia for vaginal delivery equal to that produced by 30 to 60% nitrous oxide These concentrations normally do not produce amnesia.

Side effects

nausea , vomiting

Alerts

Use of inhaled anesthetic agents has been associated with rare increases in serum potassium levels that have resulted in cardiac arrhythmias and death in pediatric patients during the postoperative period. Patient with latent as well as overt neuromuscular disease, particularly Duchenne muscular dystrophy, appear to be most vulnerable. Concomitant use of succinylcholine has been associated with most, but not all, of these cases.  

In susceptible individuals, enflurane anesthesia may trigger a skeletal muscle hypermetabolic state leading to high oxygen demand and the clinical syndrome known as malignant hyperthermia. The syndrome includes nonspecific features such as muscle rigidity, tachycardia, tachypnea, cyanosis, arrhythmias, and unstable blood pressure. 

Increasing depth of anesthesia with Enflurane may produce a change in the electroencephalogram characterized by high voltage, fast frequency, progressing through spike-dome complexes alternating with periods of electrical silence to frank seizure activity. The latter may or may not be associated with motor movement. 

Since levels of anesthesia may be altered easily and rapidly, only vaporizers producing predictable concentrations should be used. Hypotension and respiratory exchange can serve as a guide to depth of anesthesia. Deep levels of anesthesia may produce marked hypotension and respiratory depression When previous exposure to a halogenated anesthetic is known to have been followed by evidence of unexplained hepatic dysfunction, consideration should be given to use of an agent other than Enflurane

Enflurane should be used with caution in patients who by virtue of medical or drug history could be considered more susceptible to cortical stimulation produced by the drug Enflurane, like some other inhalational anesthetics, can react with desiccated carbon dioxide (CO2) absorbents to produce carbon monoxide, which may result in elevated levels of carboxyhemoglobin in some patients. Case reports suggest that barium hydroxide lime and soda lime become desiccated when fresh gases are passed through the CO2 absorber canister at high flow rates over many hours or days. When a clinician suspects that CO2 absorbent may be desiccated, it should be replaced before the administration of Enflurane.

Points of recommendation

Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

  • if you are pregnant, planning to become pregnant, or are breast-feeding
  • if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
  • if you have allergies to medicines, foods, or other substances

enflurane, as well as other general anesthetics, may cause a slight decrease in intellectual function for 2 or 3 days following anesthesia. As with other anesthetics, small changes in moods and symptoms may persist for up to 6 days after administration.

Pregnancy level

B


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