Sevoflurane

Dosage of Sevoflurane must be individualized based on the patient’s age, clinical status, and the specific surgical procedure. It is measured in terms of MAC (Minimum Alveolar Concentration), which is the concentration of the vapor in the lungs that prevents movement in 50% of patients in response to a surgical incision.

• Induction: Concentrations of up to 8% Sevoflurane may be inhaled to achieve surgical anesthesia in less than two minutes. This is typically delivered in a mixture of oxygen or oxygen/nitrous oxide.
• Maintenance: Surgical levels of anesthesia are usually maintained with concentrations ranging from 0.5% to 3.0% Sevoflurane, with or without the concomitant use of nitrous oxide.
• MAC Values: For a 40-year-old adult, the MAC of Sevoflurane is approximately 2.1% in 100% oxygen.

Sevoflurane is widely used in pediatric anesthesia due to its rapid induction and low airway irritation.

• Induction: Concentrations up to 8% are commonly used for mask induction in children.
• Maintenance: Similar to adults, maintenance levels usually fall between 0.5% and 3.0%.
• Age Considerations: MAC values are significantly higher in infants and children than in adults. For example, the MAC for a 6-month-old infant is approximately 3.3%, whereas for a neonate (less than 1 month old), it is lower, around 2.4%.

Renal Impairment

There are no specific dosage adjustment guidelines for patients with renal impairment. However, because Sevoflurane can react with carbon dioxide absorbents (like soda lime) in the anesthesia machine to produce a substance called Compound A, which has shown nephrotoxicity in laboratory animals, clinicians are advised to use fresh gas flow rates of at least 1 Liter/minute (L/min) for exposures up to 2 MAC-hours, and 2 L/min for longer procedures to minimize Compound A accumulation.

Hepatic Impairment

Because only a small fraction (2-5%) of Sevoflurane is metabolized by the liver, significant dosage adjustments are generally not required. However, caution should be exercised in patients with severe underlying hepatic conditions or those who have had previous adverse reactions to halogenated anesthetics.

Elderly Patients

The MAC of Sevoflurane decreases significantly as age increases. For an 80-year-old, the MAC is approximately 1.4% (compared to 2.1% for a 40-year-old). Anesthesia providers must titrate the dose carefully to avoid excessive cardiovascular and respiratory depression in the elderly.

Sevoflurane is not 'taken' by the patient in a traditional sense. It is administered by an anesthesiologist or a certified registered nurse anesthetist (CRNA).

• Administration: The patient breathes the vapor through a face mask, a laryngeal mask airway (LMA), or an endotracheal tube.
• Environment: It is only used in controlled clinical environments (operating rooms, MRI suites, or dental surgery centers) equipped with full monitoring and resuscitative equipment.
• Storage: The liquid bottles should be stored at room temperature (15°C to 30°C) and kept tightly capped.

Since Sevoflurane is administered continuously by a healthcare professional during surgery, the concept of a 'missed dose' does not apply. The professional monitors the concentration in real-time using an end-tidal gas analyzer to ensure the patient remains at the appropriate depth of anesthesia.

An overdose of Sevoflurane (delivering too high a concentration) can lead to severe physiological depression.

• Signs: Deep hypotension (low blood pressure), severe respiratory depression (slowed breathing), and bradycardia (slow heart rate).
• Emergency Measures: If an overdose is suspected, the anesthesia provider will immediately turn off the Sevoflurane vaporizer, increase the flow of 100% oxygen, and provide cardiovascular support (such as intravenous fluids or vasopressors) and mechanical ventilation until the drug is exhaled and the patient stabilizes.

> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance. In the case of Sevoflurane, all dosing decisions are made by the anesthesia team in real-time.

Sevoflurane is generally well-tolerated, but like all general anesthetics, it carries a risk of side effects during the 'emergence' (waking up) phase.

• Nausea and Vomiting (PONV): Postoperative nausea and vomiting are the most frequent side effects, occurring in up to 25% of patients. This can feel like a heavy 'seasickness' or an upset stomach upon waking.
• Coughing and Breath-holding: While less common than with other gases, some patients may experience a brief period of coughing or breath-holding as they wake up and the breathing tube is removed.
• Shivering (Post-anesthetic Shivering): Patients may feel intensely cold and shake uncontrollably for several minutes after waking. This is often due to the drug's effect on the body's temperature regulation center in the brain.
• Somnolence: A period of extreme drowsiness or 'fogginess' is expected as the drug clears the system.

• Agitation and Delirium: Particularly in children, 'emergence delirium' can occur. This involves the child waking up crying, thrashing, or acting inconsolable for 10-20 minutes. It is usually self-limiting and does not have long-term effects.
• Hypotension: A temporary drop in blood pressure during the procedure.
• Bradycardia or Tachycardia: The heart rate may slow down or speed up significantly during induction or maintenance.
• Increased Salivation: Excessive spit or drooling during the recovery phase.

• Arrhythmias: Irregular heart rhythms, such as premature ventricular contractions (PVCs).
• Transient Elevation in Liver Enzymes: Minor, temporary changes in liver function tests.
• Seizure-like Activity: Rare reports of 'myoclonic' movements (muscle jerks) have been noted, especially in children during induction, though these are typically not true epileptic seizures.

> Warning: While you are under anesthesia, your medical team will monitor for these. If you are at home recovering and experience any of the following, call your doctor or emergency services immediately.

• Malignant Hyperthermia (MH): This is a rare, life-threatening reaction to volatile anesthetics. Symptoms include a rapid rise in body temperature, severe muscle rigidity, and a fast heart rate. It is a medical emergency treated with a drug called dantrolene.
• Anaphylaxis: A severe allergic reaction characterized by hives, swelling of the face or throat, and difficulty breathing.
• Perioperative Hyperkalemia: In rare cases, especially in children with undiagnosed muscular dystrophy, Sevoflurane can cause a sudden release of potassium into the blood, leading to cardiac arrest.
• Hepatic Injury: Very rare cases of 'halothane-like' hepatitis (liver inflammation) have been reported, presenting as jaundice (yellowing of skin/eyes), dark urine, and abdominal pain.
• QT Prolongation: A change in the heart's electrical activity that can lead to dangerous heart rhythms.

Most side effects of Sevoflurane resolve within 24 to 48 hours as the gas is eliminated from the body. However, there is ongoing clinical discussion regarding:

• Neurocognitive Effects: There has been research into whether repeated or prolonged exposure to general anesthesia in children under age 3 affects brain development. Currently, the FDA suggests that while brief exposures are likely safe, healthcare providers should discuss the timing of elective surgeries in very young children.
• Postoperative Cognitive Dysfunction (POCD): In elderly patients, a period of confusion or memory issues may persist for several days or weeks following major surgery, though this is often attributed to the overall surgical stress rather than Sevoflurane alone.

No FDA black box warnings for Sevoflurane. However, the FDA issued a Drug Safety Communication in 2016 (updated in 2017) regarding the use of general anesthetic and sedation drugs in children under 3 years of age and in pregnant women during their third trimester, warning that repeated or lengthy use may affect fetal or childhood brain development.

Report any unusual symptoms to your healthcare provider.

Sevoflurane is a potent drug that should only be administered by professionals trained in the administration of general anesthesia. It requires continuous monitoring of vital signs, including electrocardiogram (ECG), blood pressure, oxygen saturation, and end-tidal CO2 levels. Because it causes a rapid loss of consciousness, airway management (ensuring the patient can breathe) is the highest priority.

No FDA black box warnings for Sevoflurane.

• Malignant Hyperthermia (MH) Risk: Sevoflurane can trigger MH in susceptible individuals. This is a hypermetabolic state of the skeletal muscle. Patients with a family history of MH must inform their anesthesiologist. The facility must have a 'Malignant Hyperthermia Cart' with dantrolene available.
• Perioperative Hyperkalemia: Use of inhaled anesthetics 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. This is most commonly seen in patients with latent or overt neuromuscular disease, particularly Duchenne muscular dystrophy.
• Respiratory Depression: Sevoflurane causes dose-dependent respiratory depression. Spontaneous breathing must be closely monitored, and mechanical ventilation is often required.
• Cardiovascular Depression: It can cause a dose-related decrease in blood pressure and heart rate. Caution is needed in patients with coronary artery disease or hypovolemia (low blood volume).
• Hepatic Impairment: Although rare, 'anesthetic-induced hepatitis' can occur. Patients with pre-existing liver disease or those who have had a previous reaction to halogenated anesthetics (like isoflurane or desflurane) may be at higher risk.
• Intracranial Pressure (ICP): In patients at risk for increased ICP (e.g., brain tumors or head injury), Sevoflurane should be used cautiously, often in conjunction with techniques to reduce pressure (like hyperventilation), as it can cause vasodilation in the brain.

During and immediately after Sevoflurane administration, the following must be monitored:

1. 1Continuous ECG: To detect arrhythmias or signs of heart stress.
2. 2Pulse Oximetry: To ensure adequate oxygen levels in the blood.
3. 3Non-invasive Blood Pressure: Typically measured every 3-5 minutes.
4. 4End-Tidal CO2: To ensure the patient is breathing adequately and to detect early signs of Malignant Hyperthermia.
5. 5Inspiratory/Expiratory Gas Concentration: To monitor the exact dose of Sevoflurane being delivered.
6. 6Temperature: To monitor for hypothermia or the rapid heat rise associated with MH.

Patients must NOT drive, operate heavy machinery, or make important legal decisions for at least 24 hours after receiving Sevoflurane. The drug impairs coordination, judgment, and reaction time. A responsible adult must accompany the patient home after discharge.

Alcohol should be avoided for at least 24 hours following anesthesia. Alcohol is a CNS depressant and can dangerously enhance the residual sedative effects of Sevoflurane, leading to excessive sleepiness or respiratory issues.

Discontinuation of Sevoflurane is managed by the anesthesia provider. As the gas is turned off, the patient begins to wake up. There is no 'withdrawal syndrome' in the traditional sense, but patients may experience emergence delirium or shivering as the drug levels in the brain drop.

> Important: Discuss all your medical conditions with your healthcare provider before starting Sevoflurane.

There are few absolute contraindications for drug combinations with Sevoflurane, as it is a controlled gas. However:

• Non-Selective MAOIs (Monoamine Oxidase Inhibitors): Drugs like phenelzine should ideally be discontinued 2 weeks before elective surgery. The combination can lead to unpredictable fluctuations in blood pressure and 'serotonin syndrome' risks during the perioperative period.

• Epinephrine and Sympathomimetics: Sevoflurane, like other halogenated anesthetics, can sensitize the heart to the effects of epinephrine (adrenaline). If epinephrine is injected by the surgeon (e.g., for local numbing or to stop bleeding), it can trigger dangerous ventricular arrhythmias. The dose of epinephrine should be limited.
• Calcium Channel Blockers (CCBs): Drugs like verapamil or diltiazem can worsen the hypotension (low blood pressure) and bradycardia (slow heart rate) caused by Sevoflurane due to additive effects on the heart's conduction system.
• Beta-Blockers: While often continued for heart protection, they can blunt the body's compensatory heart rate increase if Sevoflurane causes blood pressure to drop.

• Benzodiazepines and Opioids: Drugs like midazolam (Versed) or fentanyl are frequently used with Sevoflurane. They have a synergistic effect, meaning they significantly reduce the amount of Sevoflurane (the MAC) needed. Failure to reduce the Sevoflurane dose when these are used can lead to excessive sedation and respiratory depression.
• Neuromuscular Blocking Agents (Muscle Relaxants): Sevoflurane markedly potentiates (strengthens) the effects of non-depolarizing muscle relaxants like vecuronium, rocuronium, and cisatracurium. The dose of these relaxants usually needs to be reduced by 30-50% when used with Sevoflurane.
• Nitrous Oxide: Using 'laughing gas' alongside Sevoflurane reduces the required concentration of Sevoflurane by approximately 50% in adults.

• Fasting (NPO Status): While not a direct chemical interaction, patients must follow strict 'NPO' (nothing by mouth) guidelines before receiving Sevoflurane. Usually, this means no solid food for 6-8 hours and no clear liquids for 2 hours before surgery. This is to prevent 'aspiration' (vomiting and inhaling food into the lungs) while unconscious.

• St. John’s Wort: Can induce liver enzymes (CYP3A4/2E1), potentially altering the metabolism of Sevoflurane or associated drugs. It may also prolong the effects of anesthesia.
• Valerian, Kava, and Ginkgo: These can have sedative properties or affect bleeding times. Most anesthesiologists recommend stopping all herbal supplements 7-14 days before surgery.

• Inorganic Fluoride Levels: Sevoflurane metabolism releases fluoride ions. While usually harmless, this can cause a transient rise in serum fluoride levels, which might interfere with certain specialized metabolic tests.
• Glucose: Like most surgical stressors, anesthesia can cause a temporary rise in blood glucose levels.

For each major interaction, the mechanism usually involves pharmacodynamic synergy (drugs working together on the same system) or pharmacokinetic potentiation (one drug changing how another is processed). Management involves careful titration of the Sevoflurane dose by the anesthesia professional.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.

Sevoflurane must NEVER be used in the following situations:

1. 1Known or Suspected Genetic Susceptibility to Malignant Hyperthermia (MH): This is the most critical contraindication. Because Sevoflurane is a known trigger for MH, using it in a susceptible patient can lead to rapid death if not treated immediately. The mechanism involves a defect in the ryanodine receptor (RYR1) in muscle cells, leading to uncontrolled calcium release.
2. 2Known Hypersensitivity to Sevoflurane: Patients who have had a documented severe allergic reaction (anaphylaxis) to Sevoflurane or other halogenated anesthetics (e.g., isoflurane, desflurane, halothane) should not receive it.
3. 3History of Confirmed Hepatitis after Halogenated Anesthesia: If a patient has previously developed jaundice or liver failure after exposure to these gases, Sevoflurane is contraindicated due to the risk of cross-sensitivity and recurrent liver injury.

In these cases, the healthcare provider will perform a careful risk-benefit analysis:

• Severe Coronary Artery Disease: Because Sevoflurane can lower blood pressure and reduce blood flow to the heart, it must be used with extreme caution.
• Increased Intracranial Pressure (ICP): Sevoflurane can cause cerebral vasodilation (widening of blood vessels in the brain), which may further increase pressure inside the skull.
• Hypovolemia: Patients who are severely dehydrated or have lost significant blood may experience profound drops in blood pressure when Sevoflurane is administered.
• Neuromuscular Disease: Patients with conditions like Duchenne Muscular Dystrophy are at higher risk for hyperkalemia (high potassium) and cardiac arrest when exposed to Sevoflurane.

There is a high degree of cross-sensitivity between Sevoflurane and other volatile anesthetics like Isoflurane and Desflurane. If a patient is allergic to one, they are likely allergic to all drugs in this class. There is no known cross-sensitivity between Sevoflurane and intravenous anesthetics like propofol or ketamine.

> Important: Your healthcare provider will evaluate your complete medical history before prescribing Sevoflurane.

• FDA Category: Previously classified as Category B.
• Risk Summary: There are no adequate and well-controlled studies in pregnant women. However, Sevoflurane is frequently used for general anesthesia during Cesarean sections. It is known to cross the placenta rapidly.
• Labor and Delivery: Sevoflurane causes relaxation of the uterus. This can be beneficial in some cases but may increase the risk of uterine bleeding (postpartum hemorrhage) if used at high concentrations for long periods.
• Teratogenicity: Animal studies have not shown evidence of birth defects, but the FDA warns against prolonged or repeated use in the third trimester due to potential risks to the developing fetal brain.

• Passage into Milk: Small amounts of Sevoflurane may be excreted into breast milk. However, because the drug is rapidly cleared from the mother's blood via the lungs, the amount an infant would ingest is considered negligible.
• Clinical Recommendation: Most professional societies (like the ASA) state that a mother may resume breastfeeding as soon as she is awake and alert enough to hold the baby following Sevoflurane anesthesia.

• Approval: Sevoflurane is FDA-approved for use in children of all ages, including neonates.
• Benefits: It is the preferred agent for mask induction because it does not cause airway spasms or excessive coughing.
• Risks: Children have a higher risk of emergence delirium (post-op agitation). There is also the FDA warning regarding 'neurotoxicity' in children under 3 years old for procedures lasting longer than 3 hours.

• Sensitivity: Elderly patients are much more sensitive to Sevoflurane. The MAC (dose) required is significantly lower.
• Cardiovascular Risk: The elderly are at higher risk for hypotension and bradycardia.
• Cognitive Recovery: Older adults may take longer to return to their baseline mental state and are more prone to postoperative confusion.

• Compound A: As mentioned, Sevoflurane can break down into Compound A in the presence of CO2 absorbents. While animal studies show kidney damage, human studies have not conclusively proven that Sevoflurane causes kidney failure in patients with pre-existing renal disease, provided adequate gas flow rates are used.

• Metabolism: Since the liver only processes a tiny fraction of the drug, even patients with moderate cirrhosis can usually tolerate Sevoflurane. However, the anesthesia provider will monitor liver function closely post-operatively.

> Important: Special populations require individualized medical assessment.

Sevoflurane acts primarily on the GABA-A receptor complex in the central nervous system. It binds to an allosteric site on the receptor, increasing the affinity of the receptor for GABA (an inhibitory neurotransmitter). This increases the frequency and duration of the opening of the chloride ion channel, leading to neuronal hyperpolarization and a global depression of CNS activity. Additionally, it inhibits NMDA receptors (excitatory) and activates two-pore-domain potassium channels, which helps maintain a stable, non-excitable state in neurons.

• Dose-Response: The effect is strictly dose-dependent. Increasing the inspired concentration leads to deeper levels of anesthesia, lower blood pressure, and slower breathing.
• Onset: Very rapid (1-2 minutes for induction).
• Duration: The effect lasts only as long as the gas is being inhaled. Once stopped, the 'washout' from the brain is rapid.
• Tolerance: Tolerance does not develop during a single surgical procedure, though chronic exposure (e.g., in healthcare workers) is avoided due to potential health risks.

| Parameter | Value |

|---|---|

| Blood/Gas Partition Coefficient | 0.65 - 0.69 |

| Protein Binding | Negligible |

| Metabolism (Liver) | 2% - 5% (via CYP2E1) |

| Primary Metabolite | Hexafluoroisopropanol (HFIP) |

| Elimination Route | Exhalation (>95%) |

| MAC (40-year-old) | 2.1% (in 100% O2) |

• Molecular Formula: C4H3F7O
• Molecular Weight: 200.05 g/mol
• Solubility: Miscible with ethanol, ether, and chloroform; slightly soluble in water.
• Structure: 1,1,1,3,3,3-hexafluoro-2-(fluoromethoxy)propane. It is a clear, colorless, stable liquid.

Sevoflurane is a volatile liquid inhalational anesthetic. It is part of the halogenated ether family, which also includes isoflurane and desflurane. It is chemically distinct from older agents like halothane (which is an alkane) and nitrous oxide (which is an inorganic gas).