What are core differences between spinal and epidural anesthesia?

• A. Spinal Anesthesia Is A Subarachnoid, Single-Shot With Rapid Onset; Epidural Is Injected Into The Epidural Space And Can Use A Catheter For Ongoing Analgesia With Slower Onset.
• B. Spinal Anesthesia Is Injected Into The Epidural Space; Epidural Is Subarachnoid.
• C. Spinal Uses Catheter For Ongoing Analgesia; Epidural Is Single-Shot Only.
• D. Spinal Is Slower Onset; Epidural Is Rapid Onset.

Answer: (A)

The main idea is where the anesthetic is placed and how that affects how it works. Spinal anesthesia goes into the subarachnoid space, where the local anesthetic mixes with cerebrospinal fluid to quickly block nerve roots. That makes the onset rapid and the block typically dense, often delivered as a single shot for a procedure. Epidural anesthesia is injected into the epidural space, outside the dura mater. Because the drug must diffuse across the dura to reach the nerve roots, the onset is slower, but you can place a catheter in the epidural space for ongoing or repeated dosing, giving extended analgesia or anesthesia as needed.

So the best statement captures both distinctions: spinal is subarachnoid, usually a single-shot with rapid onset; epidural is in the epidural space and can use a catheter for ongoing analgesia with slower onset. The other options misplace the spaces, misstate catheter use, or misstate onset speed, which is why they don’t fit.