Sevoflurane

MECHANISM OF ACTION

The exact mechanism of action of sevoflurane is not completely understood, but it is thought to produce general anesthesia by interacting with multiple receptor systems in the central nervous system. It enhances inhibitory neurotransmission through its actions on GABA and glycine receptors, while suppressing excitatory neurotransmission by modulating nicotinic acetylcholine, serotonin, and glutamate receptors. Additionally, sevoflurane influences voltage gated and two-pore potassium channels, which further contribute to its anesthetic properties.

PHARMACOKINETICS

Absorption & distribution: Quickly absorbed via the lungs, with onset dependent on inspired concentration, ventilation, and cardiac output; its low blood/gas solubility enables rapid equilibration between alveolar and arterial partial pressures.

Metabolism: Only about 2–5% is metabolized in the liver, forming hexafluoroisopropanol and inorganic fluoride, and this process is not significantly affected by renal impairment.

Elimination: Approximately 95–98% is excreted unchanged through the lungs.

PHARMACODYNAMICS

Sevoflurane’s pharmacodynamics involve dose-dependent depression of the central nervous system, cardiovascular system, and respiratory system by enhancing inhibitory neurotransmission and inhibiting excitatory neurotransmission. Its low blood solubility contributes to rapid induction and emergence from anesthesia. Additionally, its minimal airway irritant properties make it well-suited for mask induction, particularly in pediatric patients. Factors such as age significantly influence its effects, with older patients requiring a lower minimum alveolar concentration to achieve anesthesia.

DOSAGE AND ADMINISTRATION

Sevoflurane is administered as an inhaled anesthetic through a specialized vaporizer, typically delivered via face mask, endotracheal tube, or laryngeal mask airway during general anesthesia. For induction, sevoflurane is usually started at an inspired concentration of 2% to 8%, with pediatric patients often benefiting from its low airway irritation during mask induction. In adults, induction concentrations generally range from 3% to 8%. Maintenance doses typically range from 1% to 3%, adjusted based on the patient’s age, procedure, and anesthetic depth required. The minimum alveolar concentration of sevoflurane varies with age, decreasing in elderly patients, and dosage adjustments may be necessary for those with cardiovascular or respiratory compromise. Sevoflurane is often used in combination with other anesthetics and analgesics as part of balanced anesthesia. Continuous monitoring of vital signs, oxygen saturation, end-tidal CO₂, and anesthesia depth is essential to ensure safety and effectiveness during administration.

FOOD INTERACTIONS

There are no known direct food interactions with sevoflurane; however, patients undergoing general anesthesia with sevoflurane must strictly follow preoperative fasting guidelines to reduce the risk of serious complications during surgery. The primary precaution regarding interactions is that alcohol consumption should be avoided, as it may affect anesthesia safety and effectiveness.

DRUG INTERACTIONS

Sevoflurane can interact with several drugs, including CYP450 inhibitors like cimetidine that may increase its effects, and CNS depressants such as opioids or benzodiazepines, which can enhance sedation and respiratory depression. It also potentiates neuromuscular blockers, leading to prolonged muscle relaxation. Although less common, caution is needed with drugs that sensitize the heart to catecholamines due to potential arrhythmias. Alcohol should be avoided as it may increase CNS depression and affect anesthesia safety. Careful monitoring is important when sevoflurane is used alongside other medications.

CONTRAINDICATIONS

Sevoflurane is contraindicated in patients with known or suspected sensitivity to sevoflurane or other halogenated anesthetics. It is also contraindicated in individuals susceptible to malignant hyperthermia, as well as those with certain liver or heart conditions.

SIDE EFFECTS

Common side effects:

• Nausea and vomiting.

• Agitation, confusion, or delirium.

• Dizziness, lightheadedness, or drowsiness.

• Changes in blood pressure.

• Changes in heart rate (can be fast or slow).

• Headache.

• Cough.

• Fever or chills.

• Low body temperature. 

Serious side effects:

• Malignant hyperthermia. 

• Allergic reaction. 

• Breathing problems. 

• Cardiovascular issues. 

• Liver problems. 

• Seizures . 

• Kidney problems.

OVERDOSE

Respiratory depression: Slow, shallow, or labored breathing, or complete cessation of breathing (apnea).

Cardiovascular collapse: This can involve a significant drop in blood pressure (hypotension), a slow heart rate (bradycardia), or cardiac arrest.

Central nervous system depression: Confusion, agitation, seizures, and loss of consciousness.

Other symptoms: Nausea, vomiting, and a potential risk for kidney or liver injury. 

TOXICITY

Sevoflurane toxicity may cause hepatotoxicity, nephrotoxicity, and neurotoxicity. Potential adverse effects include renal injury, respiratory depression, QT prolongation, and malignant hyperthermia. In pediatric patients, there is particular concern about neurotoxicity, as well as a risk of severe bradycardia and cardiac arrest in those with Down syndrome. The risk of renal toxicity is linked to the formation of compound A during anesthesia, especially under low fresh gas flow conditions, which the FDA advises against for certain procedures to minimize this risk.