A 25 year old male who met with a roadside accident underwent debridement and reduction of fracture of both bones of right forearm under axillary block. Commonest cause of persistent numbness and paresthesia in the right forearm and hand on the second post operative day includes all of the following, EXCEPT:

**Core Concept**
The question is testing the understanding of peripheral nerve injury or compression, particularly in the context of regional anesthesia. The axillary block involves the interruption of the brachial plexus, which provides sensory innervation to the forearm and hand.

**Why the Correct Answer is Right**
In the context of axillary block, persistent numbness and paresthesia can occur due to various reasons. However, the correct answer is the exception among the given options. The common causes include nerve ischemia or compression due to the tourniquet used during the procedure, direct trauma to the nerves during the debridement and reduction of the fracture, and nerve injury due to the prolonged compression of the nerves in the axillary block.

**Why Each Wrong Option is Incorrect**
* **Option A:** Nerve ischemia or compression due to the tourniquet used during the procedure is a possible cause of persistent numbness and paresthesia.
* **Option B:** Direct trauma to the nerves during the debridement and reduction of the fracture is another possible cause.
* **Option C:** Nerve injury due to the prolonged compression of the nerves in the axillary block is also a possible cause.

**Clinical Pearl / High-Yield Fact**
In regional anesthesia, the duration of the block can be prolonged by the use of a long-acting local anesthetic or by the compression of the nerves due to the tourniquet or direct trauma.

**Correct Answer:** D.

✓ Correct Answer: C. Systemic toxicity of local anaesthetics