Volatile Anesthetics
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Mechanism of Action: Various ion channels in the CNS involved in synaptic transmission (including GABAA, glycine, and glutamate receptors) may play a role.
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Pharmacokinetics:
- The higher the vapor pressure, the more volatile the anesthetic.
- Blood solubility determines the speed of build-up / elimination from blood / brain.
- Lower blood solubility means (faster induction/recovery).
- Inspired air → Alveolar air → Blood → Brain.
- Metabolism: hepatic.
- Exhalation: This is the predominant route of elimination.
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Pharmacodynamics:
- CNS: Unconsciousness and amnesia. ↑ cerebral blood flow (CBF).
- Respiratory System: Dose-dependent respiratory depression. Airway irritation and, during light levels of anesthesia, may precipitate coughing, laryngospasm, or bronchospasm (sevoflurane makes it more suitable). Bronchodilator (with the exception of desflurane). Inhibit hypoxic pulmonary vasoconstriction.
- Renal System: ↓ renal blood flow.
- Cardiovascular System: Myocardial depression & systemic vasodilation. HR tends to be unchanged, except desflurane. Sensitize the myocardium to the arrhythmogenic effects of catecholamines.
- Neuromuscular System: Dose-dependent ↓ in skeletal muscle tone. May precipitate malignant hyperthermia… A dramatic increase in body temperature, acidosis, electrolyte imbalance, and shock. Management is removal of triggering agent, 100% Oxygen, active cooling measures & Dantrolene (1 to 10 mg/kg).
- Hepatic System: ↓ hepatic perfusion.