Which statement accurately describes onset times for spinal versus epidural anesthesia?

• A. Epidural onset is rapid (3-5 minutes) and spinal onset is slower (10-20 minutes) with incremental dosing via catheter.
• B. Spinal onset is rapid (3-5 minutes) and epidural onset is slower (10-20 minutes) with incremental dosing via catheter.
• C. Both spinal and epidural have identical onset times.
• D. Epidural onset is faster than spinal.

Answer: (B)

Onset timing is driven by how the anesthetic is delivered. Spinal anesthesia places the drug directly into the cerebrospinal fluid, so it quickly bathes the spinal nerve roots and produces a rapid, reliable block within minutes. Epidural anesthesia sits in the epidural space and must diffuse across the dura to reach the nerve roots, making the onset slower; when a catheter is used, dosing is incremental to titrate to the desired level, which typically takes longer than a single-shot spinal. This aligns with a rapid onset for spinal (around 3–5 minutes) and a slower onset for epidural (around 10–20 minutes) with incremental dosing. The other descriptions conflict with the basic diffusion and access differences between the two techniques.