Spinal versus epidural onset: which best describes?

• A. Spinal is slow onset; epidural is fast.
• B. Epidural is never used in obstetrics.
• C. Spinal provides rapid onset with dense block, while epidural is slower and titratable with catheter.
• D. Both are identical.

Answer: (C)

Onset and block characteristics differ because of how the anesthetic is delivered. Spinal anesthesia injects local anesthetic directly into the subarachnoid space, so it reaches the cerebrospinal fluid and nerve roots almost immediately. This produces a rapid onset with a dense block that rapidly involves sensory and motor fibers. Epidural anesthesia, by contrast, places the drug into the epidural space and relies on diffusion across the dura to reach the nerve roots. That process is slower, and the initial block can be lighter, but the presence of a catheter allows continuous or repeated dosing, making the block titratable and extendable as needed.

This difference is why the description stating rapid onset with dense block for spinal and slower, titratable blockade with a catheter for epidural best fits the reality of clinical use. The statement that epidural is never used in obstetrics is incorrect, and the claim that both techniques are identical ignores their distinct onset, density, and ability to titrate.