In a differential block, which fiber is blocked two levels above sensory blockade?

In a differential block, which fiber is blocked two levels above sensory blockade?

• A. A Alpha and A Gamma
• B. A Delta
• C. B Autonomic
• D. A Beta

Answer: (C)

In differential block, the pattern of blockade depends on fiber sensitivity to local anesthetic. Autonomic fibers, specifically the small, myelinated preganglionic autonomic (B) fibers, are the most susceptible. Because of their size and myelination, they lose function earlier and at a higher level than sensory fibers. That’s why the autonomic block is seen two dermatomes above the sensory blockade. The sensory fibers (like A-delta and others) require a bit more exposure to the anesthetic, and the motor fibers (larger A-fibers) are blocked even later. So the fiber blocked two levels above the sensory blockade is the autonomic B fiber.

In differential block, the pattern of blockade depends on fiber sensitivity to local anesthetic. Autonomic fibers, specifically the small, myelinated preganglionic autonomic (B) fibers, are the most susceptible. Because of their size and myelination, they lose function earlier and at a higher level than sensory fibers. That’s why the autonomic block is seen two dermatomes above the sensory blockade. The sensory fibers (like A-delta and others) require a bit more exposure to the anesthetic, and the motor fibers (larger A-fibers) are blocked even later. So the fiber blocked two levels above the sensory blockade is the autonomic B fiber.