**Core Concept**
Accidental intra-arterial injection of thiopentone is a medical emergency that requires prompt action to prevent further complications. Thiopentone is a highly lipid-soluble barbiturate that can cause severe tissue necrosis and gangrene when injected into an artery.

**Why the Correct Answer is Right**
Removing the needle (Option A) would only worsen the situation by allowing more thiopentone to flow into the arterial circulation, exacerbating the damage. The correct course of action is to leave the needle in place and act quickly to minimize the extent of the injury. This may involve flushing the artery with a vasodilator, such as papaverine, to help displace the thiopentone and restore blood flow to the affected area.

**Why Each Wrong Option is Incorrect**
**Option B:** Intra-arterial heparin would not be effective in reversing the damage caused by thiopentone and may even worsen the bleeding.
**Option C:** While intra-arterial papaverine is a correct treatment for accidental intra-arterial injection of thiopentone, it is not a reason not to do something. The question is asking what should not be done.
**Option D:** A stellate ganglion block may be considered in some cases of accidental intra-arterial injection, but it is not the immediate step that should be taken and is not a reason not to remove the needle.

**Clinical Pearl / High-Yield Fact**
In case of accidental intra-arterial injection of thiopentone, it is essential to leave the needle in place and act quickly to minimize the extent of the injury. Flushing the artery with a vasodilator, such as papaverine, can help displace the thiopentone and restore blood flow to the affected area.

**✓ Correct Answer: A. Remove the needle**