Enflurane Inhalant
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Questions & Answers
Side Effects & Adverse Reactions
Perioperative Hyperkalemia
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. Patients 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. These patients also experienced significant elevations in serum creatinine kinase levels and, in some cases, changes in urine consistent with myoglobinuria.
Despite the similarity in presentation to malignant hyperthermia, none of these patients exhibited signs or symptoms of muscle rigidity or hypermetabolic state. Early and aggressive intervention to treat the hyperkalemia and resistant arrhythmias is recommended, as is subsequent evaluation for latent neuromuscular disease.
Malignant Hyperthermia
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. (It should also be noted that many of these nonspecificsigns may appear with light anesthesia, acute hypoxia, etc. The syndrome of malignant hyperthermia secondary to enflurane appears to be rare; by March 1980, 35 cases had been reported in North America for an approximate incidence of 1:725,000 enflurane anesthetics.) An increase in overall metabolism may be reflected in an elevated temperature (which may rise rapidly early or late in the case, but usually is not the first sign of augmented metabolism) and an increased usage of the CO
2 absorption system (hot cannister). PaO2 and pH may decrease, and hyperkalemia and a base deficit may appear. Treatment includes discontinuance of triggering agents (e.g., enflurane), administration of intravenous dantrolene sodium, and application of supportive therapy. Such therapy includes vigorous efforts to restore body temperature to normal, respiratory and circulatory support as indicated, and management of electrolyte-fluid-acid-base derangement. (Consult prescribing information for dantrolene sodium intravenous for additional information on patient management.) Renal failure may appear later, and urine flow should be sustained if possible.
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. Motor activity, when encountered, generally consists of twitching or “jerks” of various muscle groups; it is self-limiting and can be terminated by lowering the anesthetic concentration. This electroencephalographic pattern associated with deep anesthesia is exacerbated by low arterial carbon dioxide tension. A reduction in ventilation and anesthetic concentrations usually suffices to eliminate seizure activity. Cerebral blood flow and metabolism studies in normal volunteers immediately following seizure activity show no evidence of cerebral hypoxia. Mental function testing does not reveal any impairment of performance following prolonged enflurane anesthesia associated with or not associated with seizure activity.
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.
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Uses
Enflurane may be used for induction and maintenance of general anesthesia. Enflurane may be used to provide analgesia for vaginal delivery. Low concentrations of enflurane (see
DOSAGE AND ADMINISTRATION) may also be used to supplement other general anesthetic agents during delivery by Cesarean section. Higher concentrations of enflurane may produce uterine relaxation and an increase in uterine bleeding
History
There is currently no drug history available for this drug.
Other Information
Enflurane, USP, a nonflammable liquid administered by vaporizing, is a general inhalation anesthetic drug. It is 2-chloro-1,1,2-trifluoroethyl difluoromethyl ether, (CHF
2OCF
2CHFCl). The boiling point is 56.5°C at 760 mm Hg, and the vapor pressure (in mm Hg) is 175 at 20°C, 218 at 25°C, and 345 at 36°C. Vapor pressures can be calculated using the equation:
| log10Pvap= A + B A = 7.967 T B = -1678.4 |
T = ° C + 273.16 (Kelvin)
Enflurane is a clear, colorless, stable liquid whose purity exceeds 99.9% (area percent by gas chromatography). No stabilizers are added as these have been found, through controlled laboratory tests, to be unnecessary even in the presence of ultraviolet light. Enflurane is stable to strong base, does not decompose in contact with soda lime (at normal operating temperatures) and does not react with aluminum, tin, brass, iron or copper. The partition coefficients of enflurane at 25°C are 74 in conductive rubber and 120 in polyvinyl chloride
Sources
Enflurane Inhalant Manufacturers
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Piramal Critical Care Inc.
![Enflurane Inhalant [Piramal Critical Care Inc.]](/wp-content/themes/bootstrap/assets/img/loading2.gif)
Enflurane Inhalant | Piramal Critical Care Inc.
The concentration of enflurane being delivered from a vaporizer during anesthesia should be known.
This may be accomplished by using:1) vaporizers calibrated specifically for enflurane;
2) vaporizers from which delivered flows can be calculated.
Preanesthetic Medication
Preanesthetic medication should be selected according to the need of the individual patient, taking into account that secretions are weakly stimulated by enflurane and that enflurane does not alter heart rate. The use of anticholinergic drugs is a matter of choice.
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 possibleCNS 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. See also the information on the effects of enflurane on uterine contraction contained in the CLINICAL PHARMOCOLOGY section.
Cesarean Section
Enflurane should ordinarily be administered in the concentration range of 0.5 to 1% tosupplement other general anesthetics. See also the information on the effects ofenflurane on uterine contraction contained in the CLINICAL PHARMACOLOGYsection
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