Isoflurane
Isoflurane
Physical Properties
Effects on organ system
Biotransformation and toxicity
Contraindications
Drug Interactions
-MAC value: 1.2 %
-vapor pressure: 240mmHg at 20 degrees celcius
-pungent odor
-nonflammable
-chemical isomer of enflurane
Central Nervous System
-decreases CMR02 (at 2MAC produces electrically silent EEG which may provide come cerebral protection against ischemia)
-increases CBF
-increases ICP (increased ICP may be reversed with hyperventilation)
Cardiovascular System
-in vivo: mild cardiac depressant
-decreased systemic vascular resistance
-resultant decrease in mean arterial blood pressure
-decreased arterial blood pressure stimulated the preserved carotid baroreceptor which increases heart rate
-decreased arterial pressure and increased heart rate generally leads to a maintained cardiac output
-rapid increase in concentration may transiently increase heart rate, arterial pressure and norepinephrine levels
-coronary artery vasodilation (less than nitroglycerin effects)
-coronary steal phenomena possibilities
Coronary steal phenomena:
-coronary arteries that have atherosclerotic plaque lesions generally are unable to further vasodilate
-therefore intense coronary artery vasodilation from normal vessels may divert blood from fixed stenotic (maximally dilated) vessels
-would lead to decreased coronary blood flow to already ischemia stenotic vessels and increased blood flow to normal vessels
Respiratory System
-increased respiratory rate (tachypnea less pronounced with isoflurane compared to other volatile anesthetics)
-decreased tidal volume
-resultant decreased alveolar ventilation (more pronounced fall in minute ventilation due to less increased respiratory rate)
-blunted response to elevating levels of PaC02 or hypoxia
-good bronchodilator
Hepatic System
-reduces hepatic blood flow
-possibly better oxygen supply to liver with isoflurane in comparison with halothane and enflurane
-minimal effect on liver function tests
Renal System
-decreases renal blood flow
-decreases GFR
-decreases urinary output
Neuromuscular System
-relaxes skeletal muscles
biotransformation and toxicity
-isoflurane is metabolized in the liver to end products of trifluoracetic acid
-flouride ions rise but extremely unlikely to cause nephrotoxicity even in combination with enyzme inducers
-upto 20 MAC-hours of isoflurane may lead to flouride ion concentration greater than 50 umol/L without detectable renal dysfunction
-isoflurane has limited metabolism which reduces the possible risk of significant hepatic dysfunction
contraindications
-no major contraindications
-controvery regarding coronary steal phenomena
drug interactions
-epinephrine may be safely administered upto 4.5 ug/kg
-prolonged duration of action of nondepolarizing muscle relaxants (NDMR)
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