Neuroaxial Block
Spinal and Epidural Anesthesia
Spinal anesthesia is produced by injecting very low doses of LA (e.g., 50mg Lidocaine) via lumbar puncture into the cerebrospinal fluid below the termination of the spinal cord.
The LA diffuses in the CSF and produces dense anesthesia extending cephalic from the sacral dermatomes to as high as the lower cervical dermatomes.
A single dose of LA through fine-gauge (22- to 29-gauge) needle is usually injected, which results in a limited duration of anesthesia, but catheters can be placed in the subarachnoid space for prolonged anesthesia.
Spinal LA blocks somatic and visceral sensory afferent nerves, as well as efferent motor and autonomic (sympathetic) fibers. Sensory anesthesia, muscle relaxation and sympathetic block are the result of this technique
Spinal anesthesia is usually chosen for procedures performed in the dermatomes at or below the midabdonan.
Epidural anesthesia is produced by injection of LA into the epidural space outside the dura mater.
An epidural injection requires significantly more LA in both volume and dose than a spinal injection, but the injection can be made anywhere from the cervical epidural space to the sacral hiatus (caudal anesthesia).
The spinal nerves are blocked most intensely at the site of injection and less intensely both above and below that site.
Compared to spinal anesthesia, epidural anesthesia is often performed through a catheter introduced into the epidural space through a large (16- to 18-gauge) needle.
The catheter provides flexibility for prolonged anesthesia as well as prolonged analgesia for days into the postoperative period with infusion of dilute LA.
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