Final answer:
The nurse should first obtain a stat 12-lead ECG for Mr. Ocampo, as it is critical for diagnosing a potential myocardial infarction or angina and guiding further treatment.
Step-by-step explanation:
The first intervention the nurse should implement for treating Mr. Ocampo's chest pain is A. Obtain a stat 12-lead ECG. Since Mr. Ocampo is experiencing sharp chest pains that radiate to the left shoulder, this could indicate an acute myocardial infarction (MI) or angina, and an ECG is essential for quick diagnosis. The ECG can help determine if the discomfort is heart-related and guide further treatment. Although administering oxygen, sublingual nitroglycerin, and morphine sulfate are part of the treatment, these should follow the initial assessment provided by the ECG.