Sevoflurane
**Sevoflurane** is a highly volatile, halogenated inhalational anesthetic widely used in veterinary medicine for the induction and maintenance of general anesthesia. Key pharmacological characteristics include: * **Low Blood:Gas Partition Coefficient (0.6)**: This allows for exceptionally rapid alveolar-to-arterial equilibration, resulting in much faster induction and recovery times compared to isoflurane or halothane. * **Non-pungent Odor**: Unlike isoflurane, sevoflurane is not irritating to the airway, making it the preferred agent for **mask or chamber inductions** in exotic species, fractious felines, and pediatric patients. * **Hemodynamic Stability**: It tends to cause less profound hypotension than isoflurane, making it particularly useful in debilitated or geriatric patients. **Clinical Pearl**: Because anesthetic depth can change very rapidly with sevoflurane, vigilant monitoring is required to prevent accidental anesthetic overdose during maintenance.
Mechanism: The precise mechanism of inhalant anesthetics remains incompletely elucidated, but they primarily act by disrupting synaptic transmission within the central nervous system. * **Lipid Matrix Interaction** โ Alters the function of neuronal membrane proteins. * **GABA_A Receptors** โ Potentiates inhibitory neurotransmission, leading to profound CNS depression. * **NMDA Receptors** โ Antagonizes excitatory glutamatergic signaling. * **Glycine Receptors** โ Enhances inhibitory signaling in the spinal cord, contributing to skeletal muscle relaxation. Due to its **low solubility in blood**, minimal amounts of sevoflurane need to dissolve before alveolar partial pressures equilibrate with arterial partial pressures, driving its rapid onset and offset of action.
Dosing by species
- Anesthesia Induction (Mask/Chamber) ยท starting at a concentration of around 4-4.5%. Maximum concentration (8%) ยท Inhalation ยท Once ยท Until loss of consciousness ยท Reduce concentration as soon as the animal loses consciousness.
- Anesthesia Maintenance (Circle System) ยท vaporizer setting of 3% for a circle system is a reasonable initial concentration ยท Inhalation ยท Continuous ยท Duration of procedure ยท MAC is reported as 2.58%
- Induction of anaesthesia (unpremedicated) ยท 6-8% inspired concentration ยท Inhalational ยท continuous ยท until induced ยท Dose should be adjusted according to individual requirement and concurrent drugs.
- Maintenance of surgical anaesthesia ยท MAC is approximately 2.5% (expired concentration) ยท Inhalational ยท continuous ยท duration of surgery ยท Adjust concentration according to clinical assessment of anaesthetic depth. Administration of other anaesthetic agents and opioids reduces the dose requirement.
- Anesthesia Maintenance ยท MAC = 1.97-2.66% ยท Inhalation ยท Continuous ยท Duration of procedure ยท Monitor closely for malignant hyperthermia.
- Anesthesia ยท Titrate to effect ยท Inhalation ยท Continuous ยท Duration of procedure ยท Can cause temporary decreases in erythrocyte and white cell counts and total protein (reverses within 2 hours post-discontinuation).
Routes of administration
Contraindications
- Patients with a history or predilection towards malignant hyperthermia
- Known hypersensitivity to sevoflurane or other halogenated anaesthetics
- Known or suspected susceptibility to malignant hyperthermia
Adverse effects
- Dose-dependent hypotension
- Dose-dependent respiratory depression
- Gastrointestinal effects (nausea, vomiting, ileus)
- Myocardial depression and bradycardia (less than halothane)
- Malignant hyperthermia (rare but life-threatening)
- Temporary decreases in erythrocyte, white cell counts, and total protein in ferrets
- Agitation or excitement during rapid recovery
- Neonatal depression (crosses the placental barrier)
Drug interactions
- Aminoglycosides, Lincosamides ยท May enhance neuromuscular blockade
- Barbiturates (phenobarbital, pentobarbital) ยท May increase concentrations of inorganic fluoride
- Non-depolarizing neuromuscular blocking agents (atracurium, pancuronium, vecuronium) ยท Additive neuromuscular blockade may occur
- Isoniazid ยท May increase concentrations of inorganic fluoride
- Midazolam ยท May potentiate sevoflurane effects; decrease MAC
- Opiates ยท May potentiate sevoflurane effects; decrease MAC
- St. John's Wort ยท Increased risk for anesthetic complications; recommend discontinuing 5 days in advance of surgery
- Succinylcholine ยท Sevoflurane may enhance effects
- Sympathomimetics (dopamine, epinephrine, norepinephrine, ephedrine) ยท Sensitizes the myocardium to sympathomimetics (less than halothane); arrhythmias may still result
- Tramadol ยท May decrease MAC requirements
- Verapamil ยท May cause cardiodepression
- Sedatives (e.g., alpha-2 agonists, phenothiazines) ยท Reduces the concentration of sevoflurane required to achieve surgical anaesthesia (MAC reduction). ยท major
Monitoring
- Respiratory rate, rhythm, and ventilatory status (capnography recommended)
- Cardiac rate and rhythm (ECG)
- Blood pressure (especially in 'at risk' or geriatric patients)
- Level of anesthetic depth (jaw tone, palpebral reflex, eye position)
- Body temperature (monitor for hypothermia or sudden spikes indicating malignant hyperthermia)
- Respiratory rate, rhythm, and depth (Capnography/ETCO2 highly recommended)
- Arterial blood pressure (hypotension is dose-dependent)
- Heart rate and rhythm (ECG)
- Anaesthetic depth (jaw tone, palpebral reflex, eye position)
- Pulse oximetry (SpO2)
- Body temperature
Overdose
In the event of an overdosage, **immediately discontinue sevoflurane administration**. * Maintain a patent airway. * Flush the breathing circuit with 100% oxygen. * Support respiratory function with positive pressure ventilation if necessary. * Support cardiac function and treat severe hypotension with IV fluids and sympathomimetics as clinically indicated.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.