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Volatile Gases

Volatile Gases (e.g. desflurane, sevoflurane, isoflurane): Physiology & clinical findings Volatile agent (gas) delivered to the lungs Mean alveolar concentration of gas increases Gas enters the bloodstream via alveolar gas exchange Gas dissolves into lipid membranes within the central nervous system ↓ Pre-synaptic release of excitatory neurotransmitters (N- methyl-D-aspartate (NMDA), acetylcholine, serotonin, & glutamate) Inhibition of post- synaptic excitatory neurotransmitter receptors (NMDA, acetylcholine, serotonin, & glutamate) Distortion of electrophysiology of post-synaptic sodium channels Activation of post- synaptic potassium channels ↑ Presynaptic release of gamma- aminobutyric Post-synaptic cell acid (GABA) hyperpolarization Impaired neuronal depolarization ↓ Excitatory post- synaptic input ↑ Inhibitory post- synaptic input Disruption of synaptic transmission in cerebral cortex, basolateral amygdala, hippocampus, etc. Cerebral vasodilation & ↑ cerebral blood flow Authors: Punit Bhatt Billy Sun Reviewers: Priyanka Grewal Luiza Radu Melinda Davis* *MD at time of publication ↓ Pre-synaptic reuptake of GABA Activation of post- synaptic GABA receptors Amnesia Loss of consciousness ↑ Intracranial pressure Compression of brainstem resulting in stimulation of the vomiting region Nausea & Vomiting Legend: Disruption of potassium signaling in cerebral & systemic vasculature Decreased systemic vascular resistance Disruption of calcium signaling in cardiac myocytes Induction of Anesthesia Impaired smooth muscle contractility Negative inotropic effect Hypotension ↓ Stroke volume & consequently decreased cardiac output Tachycardia Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Disruption of synaptic transmission in medullary, respiratory, & phrenic motor neurons Neuromuscular blockade QT Prolongation Torsades de Pointes (Polymorphic Ventricular Tachycardia) Respiratory depression Hypercapnia (Elevated CO2 concentration in the blood) Muscle relaxation Unregulated release of calcium in susceptible patients Malignant hyperthermia (a life-threatening reaction to certain anesthetics)** ** See malignant hyperthermia slide Published Aug 12, 2025 on www.thecalgaryguide.com