Sevoflurane

Introduction

Sevoflurane is a fluorinated methyl isopropyl ether and is one of the most commonly used volatile anesthetic agents worldwide. Its key clinical points are its non-pungent odor and low blood-gas solubility (0.65), which allow for rapid induction and emergence. This makes it the gold standard for inhalational inductions, particularly in children.

Formulation & Color Coding

Formulation:

Sevoflurane is a volatile liquid at room temperature. It is formulated without additives and is presented in a clear, colorless solution.

Color Coding:

This is a critical safety feature! Sevoflurane is universally color-coded YELLOW. This yellow identifier is found on:

• The bottle cap and label
• The specific filling port on the vaporizer designated for sevoflurane.
• The plastic keyed-filler device that prevents you from putting the wrong agent into the wrong vaporizer.

Always check the color code before filling a vaporizer to prevent dangerous cross-filling.

Mechanism of Action

Like all volatile anesthetics, the exact mechanism is complex and multifactorial. The prevailing theory is that sevoflurane (and its cousins) enhances the activity of inhibitory receptors in the brain (like GABA_A and glycine receptors) and inhibits excitatory receptors (like NMDA receptors). This overall potentiation of inhibition and reduction of excitation leads to the triad of anesthesia: unconsciousness, amnesia, and immobility.

Uses & Indications

Sevoflurane is used for the induction and maintenance of general anesthesia in inpatient and outpatient surgery in adults and pediatrics.

• Primary Use: Inhalational Induction. Its non-pungent odor makes it the agent of choice for mask inductions, especially in children and anxious adults.
• Maintenance of Anesthesia: Used for a wide variety of surgical cases across all specialties.
• Specific Patient Populations: Particularly beneficial for patients with reactive airway disease (asthma, COPD) due to its bronchodilatory properties.
• Cardiac Anesthesia: Often used due to its relative hemodynamic stability compared to other agents.

Dosage & Administration

Dosage is titrated to effect using the concept of Minimum Alveolar Concentration (MAC).

MAC Values:

• Age 40: 2.05%
• Age 60: 1.60%
• Term Neonate: 3.3%
• Infant (1-6 months): ~3.0%
•  Child (1-5 years): ~2.5%

Induction

• Adults: Start at 0.5-1% and increase by 0.5% every few breaths. For a single-breath vital capacity induction, use 4-5% with 100% O₂.
• Pediatrics: Start at 6-8% in 100% O₂ with high fresh gas flows (6-8 L/min).
• Maintenance: Typically 1-2.5 MAC (usually between 1.5% – 4%), balanced with opioids, benzodiazepines, or other adjuncts to allow lower volatile concentrations.
• Emergence: Turn off the vaporizer and increase fresh gas flow to high (e.g., 10 L/min) to wash out the agent.

Pharmacokinetics

• Onset/Induction: Thanks to its low blood-gas solubility, alveolar concentrations rise quickly, leading to a fast onset of action.
• Offset/Emergence: Its low solubility means it is washed out quickly, leading to rapid emergence.
• Metabolism: Approximately 3-5% is metabolized by liver CYP2E1 to hexafluoroisopropanol (HFIP), inorganic fluoride, and CO₂. The clinical significance of fluoride release is minimal.

Pharmacodynamics

• CVS: Dose-dependent hypotension** via vasodilation and mild myocardial depression. Does not significantly sensitize the heart to catecholamines.
• Respiratory: Dose-dependent respiratory depression. It is a potent bronchodilator.
• CNS: Increases cerebral blood flow (CBF) and can increase intracranial pressure (ICP). Can trigger epileptiform EEG activity.
• Renal: Metabolism produces Compound A when interacting with desiccated CO₂ absorbents. The US FDA recommends using fresh gas flows of at least 1 L/min for procedures under 2 MAC-hours and at least 2 L/min for longer procedures.

Contraindications

• Known or Suspected Genetic Susceptibility to Malignant Hyperthermia (MH). Sevoflurane is a potent triggering agent.
• Known hypersensitivity to sevoflurane or to other halogenated agents.
• A history of severe post-operative hepatic injury following sevoflurane anesthesia where other causes have been excluded.
• In patients with raised intracranial pressure, unless the patient is already mechanically ventilated and the depth of anesthesia is carefully controlled.

Key Advantages

• Non-pungent & Pleasant: The number one choice for inhalational inductions.
• Rapid Onset & Offset: Ideal for short procedures and day surgery.
• Hemodynamic Stability & Bronchodilation: Great for patients with cardiac or respiratory comorbidities.

Potential Drawbacks

• Compound A: Always check your fresh gas flow! Avoid prolonged low-flow anesthesia with desiccated absorbent.
• Emergence Agitation: Common in pediatric patients. Mitigate with good analgesia, dexmedetomidine, or a calm emergence environment.
• Postoperative Nausea and Vomiting (PONV): A recognized risk factor.
• Malignant Hyperthermia (MH): Always have a stocked MH cart accessible.

Clinical Pearls for the Trainee

1. For a smooth pediatric induction: Set your sevoflurane to 8%, your fresh gas flow to 6-8 L/min, and use a scented mask.
2. Check the Absorber: If the CO₂ absorbent is exceptionally dry, change it for long cases.
3. For rapid emergence: Turn the vaporizer off early and increase FGF. Ensure analgesia is optimal first!
4. THE GOLDEN RULE: YELLOW for YELLOW. Never force an agent into a vaporizer. If it doesn’t fit easily, you have the wrong bottle for the wrong vaporizer.

Sevoflurane is a fantastic, versatile agent. Understanding its strengths and respecting its weaknesses will make you a safer and more effective anesthetist.