Enflurane

Listen to Audio

physical properties
effects on organ system
biotransformation and toxicity
contraindications
drug interactions

physical properties
-MAC value: 1.7 %
-vapor pressure: 175 mmHg at 20 degrees celcius
-halogenated ether
-mild, sweet odor
-nonflammable at clinical concentrations

Effects on organ systems

Central Nervous System
-decreased CMR02 (unless seizure activity is induced)
-increased CBF
-increased ICP
-increased CSF secretion and increased resistance to CSF outflow
-association with tonic clonic seizure activity followed by high voltage high frequency EEG patterns
-high concentrations of enflurane in the setting of hypocapnia may exacerbate epileptiform activity

Cardiovascular System
-enflurane decreases both myocardial contractility and systemic vascular resistance
-lowered mean arterial pressure
-lowered cardiac output
-lowered myocardial oxygen consumption
-increase in heart rate due to decreased arterial pressure
-sensitizes myocardium to epinephrine induced dysrhythmias usually at a dose > 4.5 ug/kg

Respiratory System
-increases respiratory rate
-decreases tidal volume
-resultant decrease in alveolar ventilation
-increased resting PaC02
-decreased response to an elevated PaC02
-decreased/abolished hypoxic drive
-bronchodilation
-depressed mucociliary function

Hepatic System
-decreases hepatic blood flow

Renal System
-decreases renal blood flow
-decreases GFR
-decreases urinary output
-enflurane metabolites are nephrotoxic (discussed more in biotransformation and toxicity)

Neuromuscular System
-relaxes skeletal muscles
-prolongs duration of nondepolarizing muscle relaxants (NDMR)

biotransformation and toxicity
-flouride ions are the metabolite of enflurane
-flouride ions concentrations are far less than metabolism of methoxyflurane
-renal dysfunction with the use and metabolism of enflurane is unlikely
-nearly after 10 MAC-hours of enflurane, flouride ion concentrations were less than 40 umol/L in healthy patients
-flouride ion concentrations may lead to mild reduction concentrating abilities of the renal tubules in values of 40 umol/L

contraindications
-may best be avoided in patients with pre-existing renal disease
-may best be avoided in patients with history of seizure disorders
-may best be avoided in patients with history of increased ICP or decreased intracranial compliance

drug interactions
-isoniazid induces deflourination of enflurane possibly from stimulating the cytochrome P450 2EI
-prolongs duration of nondepolarizing muscle relaxants (NDMR)