Final answer:
A patient with a calcium level of 8.9 mg/dL is at potential risk for Digoxin toxicity due to the presence of hypocalcemia, which can enhance the effects of Digoxin on the heart.
Step-by-step explanation:
The patient at potential risk for Digoxin toxicity would be B. A patient with a calcium level of 8.9. Digoxin is a medication that helps to regulate the heartbeat but can become toxic if certain electrolyte imbalances are present. A calcium level of 8.9 mg/dL is considered low (hypocalcemia), which can put a patient at higher risk for Digoxin toxicity. Hypocalcemia can potentiate the effects of Digoxin on heart tissue, making toxicity more likely. In contrast, the other patients (A patient with Cushing's syndrome taking Laxis 20 mg IV twice a day, A patient with a potassium level of 3.8, and A patient presenting with painful muscle spasms and positive Trousseau's sign) do not present obvious risk factors directly associated with increased likelihood of Digoxin toxicity.