七氟醚
**七氟醚 (Sevoflurane)** 是一種高揮發性的鹵素類吸入性麻醉劑，廣泛應用於獸醫學中的全身麻醉誘導與維持。 主要藥理特徵包括： * **低血液/氣體分配係數 (0.6)**：這使得肺泡與動脈間的平衡極為迅速，與異氟醚 (Isoflurane) 或氟烷 (Halothane) 相比，其麻醉誘導與甦醒時間大幅縮短。 * **無刺激性氣味**：與異氟醚不同，七氟醚不會刺激呼吸道，是特寵、易怒貓咪及幼年動物進行**面罩或麻醉箱誘導**的首選藥物。 * **血流動力學穩定**：與異氟醚相比，它引起的低血壓程度較輕，特別適合用於虛弱或老年的病患。 **臨床要點**：由於七氟醚能極快速地改變麻醉深度，在麻醉維持期間需要密切監測，以防止意外的麻醉過量。
作用機制: 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** → Alters the function of neuronal membrane proteins. * **GABA_A Receptors** → Potentiates inhibitory neurotransmission, leading to profound CNS depression. * **NMDA Receptors** → Antagonizes excitatory glutamatergic signaling. * **Glycine Receptors** → 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.
各物種劑量
- Anesthesia Induction (Mask/Chamber) · starting at a concentration of around 4-4.5%. Maximum concentration (8%) · Inhalation · Once · Until loss of consciousness · Reduce concentration as soon as the animal loses consciousness.
- Anesthesia Maintenance (Circle System) · vaporizer setting of 3% for a circle system is a reasonable initial concentration · Inhalation · Continuous · Duration of procedure · MAC is reported as 2.58%
- Induction of anaesthesia (unpremedicated) · 6-8% inspired concentration · Inhalational · continuous · until induced · Dose should be adjusted according to individual requirement and concurrent drugs.
- Maintenance of surgical anaesthesia · MAC is approximately 2.5% (expired concentration) · Inhalational · continuous · duration of surgery · Adjust concentration according to clinical assessment of anaesthetic depth. Administration of other anaesthetic agents and opioids reduces the dose requirement.
- Anesthesia Maintenance · MAC = 1.97-2.66% · Inhalation · Continuous · Duration of procedure · Monitor closely for malignant hyperthermia.
- Anesthesia · Titrate to effect · Inhalation · Continuous · Duration of procedure · Can cause temporary decreases in erythrocyte and white cell counts and total protein (reverses within 2 hours post-discontinuation).
- Anesthesia Maintenance · MAC = 3.3% · Inhalation · Continuous · Duration of procedure
給藥途徑
禁忌症
- Patients with a history or predilection towards malignant hyperthermia
- Known hypersensitivity to sevoflurane or other halogenated anaesthetics
- Known or suspected susceptibility to malignant hyperthermia
不良反應
- 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)
藥物相互作用
- Aminoglycosides, Lincosamides · May enhance neuromuscular blockade
- Barbiturates (phenobarbital, pentobarbital) · May increase concentrations of inorganic fluoride
- Non-depolarizing neuromuscular blocking agents (atracurium, pancuronium, vecuronium) · Additive neuromuscular blockade may occur
- Isoniazid · May increase concentrations of inorganic fluoride
- Midazolam · May potentiate sevoflurane effects; decrease MAC
- Opiates · May potentiate sevoflurane effects; decrease MAC
- St. John's Wort · Increased risk for anesthetic complications; recommend discontinuing 5 days in advance of surgery
- Succinylcholine · Sevoflurane may enhance effects
- Sympathomimetics (dopamine, epinephrine, norepinephrine, ephedrine) · Sensitizes the myocardium to sympathomimetics (less than halothane); arrhythmias may still result
- Tramadol · May decrease MAC requirements
- Verapamil · May cause cardiodepression
- Sedatives (e.g., alpha-2 agonists, phenothiazines) · Reduces the concentration of sevoflurane required to achieve surgical anaesthesia (MAC reduction). · major
監測
- 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
過量
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.
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