**Core Concept**
The question tests the understanding of **local anesthetic toxicity**, specifically the consequences of accidental intravenous administration. Local anesthetics work by blocking **sodium channels** in neurons, preventing the initiation and transmission of nerve impulses.

**Why the Correct Answer is Right**
Accidental intravenous administration of a local anesthetic can lead to **systemic toxicity**, affecting the central nervous and cardiovascular systems. The most significant adverse consequences include seizures, coma, and cardiac arrest due to the blockade of **sodium channels** in the heart, leading to arrhythmias.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while local anesthetic toxicity can cause CNS effects, it is not the most significant consequence.
**Option B:** Incorrect as it is not directly related to the immediate effects of intravenous local anesthetic administration.
**Option C:** Incorrect because, although relevant, it does not encompass the full scope of the most significant adverse consequences.

**Clinical Pearl / High-Yield Fact**
The key to managing local anesthetic systemic toxicity is early recognition and prompt intervention, including seizure management and supportive care for cardiovascular instability.

**Correct Answer:** D. Cardiovascular collapse