While ambulating in the hallway following an appendectomy yesterday, a client complains of chest tightness and shortness of breath. Which action should the practical nurse (PN) implement first?

A. Administer sublingual nitroglycerin: Not appropriate without confirming cardiac ischemia and provider order. B. Assist the client back to the room: Delays immediate safety measures; sitting down is faster. C. Obtain a 12-lead electrocardiogram: Important but comes after ensuring client safety and reducing workload on the heart. D. Have the client sit down in the hall: First action is to stop activity and reduce oxygen demand while further assessment and interventions are arranged.