For lumbar epidural anaesthesia, which parameter chiefly determines the number of dermatomal segments blocked?

• A Volume of the injectate ✓
• B Concentration of the solution
• C Baricity of the solution
• D Speed of injection alone

Explanation

In the epidural space, spread of drug depends on how far the injected volume distributes along the longitudinal fat-filled compartment, so volume sets the number of segments blocked, while concentration determines the density of block, that is sensory versus motor quality. Baricity governs distribution only within cerebrospinal fluid and applies to spinals, and injection speed modifies spread only marginally. This volume-versus-concentration principle distinguishes epidural dosing from spinal dosing, where mass of drug dominates.

Reference: Cousins and Bridenbaugh's Neural Blockade in Clinical Anesthesia and Pain Medicine, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.