**Core Concept**
Succinylcholine is a depolarizing neuromuscular blocker that mimics the action of acetylcholine at the neuromuscular junction, leading to muscle contraction and eventually paralysis. However, in patients with muscle damage or denervation, such as paraplegic individuals, succinylcholine can cause the release of potassium ions from the damaged muscle cells, leading to hyperkalemia.

**Why the Correct Answer is Right**
When succinylcholine is administered to a paraplegic patient, it can cause depolarization of the muscle cells, leading to an influx of sodium ions into the cells. This results in an efflux of potassium ions from the cells into the bloodstream, causing a rapid increase in serum potassium levels, or hyperkalemia. Hyperkalemia can lead to cardiac dysrhythmias, conduction abnormalities, and ultimately cardiac arrest if left untreated. The rapid increase in potassium levels can also activate the sodium-potassium pump, leading to further depolarization of the cardiac myocytes and increased excitability.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypercalcemia is unlikely to be the cause of cardiac arrest in this scenario, as it would more likely cause vasoconstriction and hypertension rather than cardiac dysrhythmias.

**Option C:** Anaphylaxis is a severe allergic reaction that can occur in response to succinylcholine, but it would typically present with symptoms such as hypotension, bronchospasm, and urticaria, rather than cardiac dysrhythmias.

**Option D:** Hypermagnesemia can cause cardiac arrest, but it would typically present with symptoms such as muscle weakness, respiratory depression, and hypotension, rather than cardiac dysrhythmias.

**Clinical Pearl / High-Yield Fact**
Succinylcholine should be used with caution in patients with muscle damage or denervation, as it can cause a rapid release of potassium ions from the damaged muscle cells, leading to hyperkalemia and cardiac complications. A pre-treatment dose of neostigmine or edrophonium can be used to detect patients at risk of succinylcholine-induced hyperkalemia.

**Correct Answer Line**
✓ Correct Answer: B. Hyperkalemia