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Neuraxial anesthesia

Neuraxial anesthesia: Mechanism of action and complications Spinal anesthesia Epidural anesthesia Anesthetic injected into epidural space (surrounding spinal cord) Blood vessel punctured Blood accumulates in epidural space Epidural hematoma Inhibits motor nerve conduction (least sensitive nerve fibers to anesthetics) Anesthetic injected into cerebrospinal fluid (CSF) in the subarachnoid space Punctured dura mater Cerebrospinal fluid leak Decrease cerebrospinal fluid pressure Vasodilation of cerebral blood vessels Post-dural puncture headache Inhibits sympathetic nerve conduction (most sensitive nerve fibers to anesthetics) Anesthetics diffuse across axon membranes & blocks voltage-gated sodium channel in nerve fibers ↓ Sodium ion flow into neuron Nerve fibers unable to depolarize & reach threshold to trigger action potential Inhibits sensory nerve conduction Cardiac sympathetic nerve fibers inhibited ↓ Norepinephrine release Unopposed parasympathetic (rest and digest) activity Parasympathetic nerves release acetylcholine (Ach) ACh binds to muscarinic receptors on smooth muscle ↑ Peristalsis ↑ Bowel motility C-fibre nerve fibers (unmyelinated) inhibited Loss of pain & temperature sensation A-delta nerve fibers (thinly myelinated) inhibited Loss of pinprick, pain & temperature sensation A-beta nerve fibers (myelinated) inhibited Loss of vibration, touch & pressure sensation A-alpha nerve fibers (heavily myelinated) inhibited Loss of proprioception Phrenic nerve fibers inhibited Diaphragm paralysis Impaired diaphragm contraction Apnea (temporary cessation of breathing) Loss of motor function ↓ Cardiac pacemaker activity Bradycardia (slow heart rate) Inhibits smooth muscle tone of blood vessels ↓ Systemic vascular resistance Authors: Shiva Ivaturi Reviewers: Run Xuan (Karen) Zeng, Luiza Radu, Julia Haber* *MD at time of publication Vasodilation Hypotension Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published Feb 24, 2025 on www.thecalgaryguide.com