The nurse is caring for a client in the post anesthesia care unit (PACU) who underwent a thoracotomy two hours ago. The nurse observes vital signs of a heart rate of 140 beats/minute, a respiratory rate of 26 breaths/minute, and a blood pressure of 140/90 mm Hg. Which intervention is most important for the nurse to implement?

A. Administer IV fluid bolus as prescribed by the healthcare provider is not the priority unless there is evidence of hypovolemia or shock, which isn't indicated by the current vital signs alone. B. Medicate for pain and monitor vital signs according to protocol is the most important intervention. The client's elevated heart rate, respiratory rate, and blood pressure are likely due to inadequate pain control following a thoracotomy, a major surgical procedure known for causing significant postoperative pain. Managing the pain is crucial because uncontrolled pain can lead to increased sympathetic nervous system activity, resulting in tachycardia, hypertension, and tachypnea. Addressing the pain effectively will help stabilize these vital signs. C. Encourage the client to splint the incision with a pillow to cough and deep breathe is an important postoperative intervention to prevent complications such as atelectasis, but it should be done after pain is adequately controlled, as pain can inhibit the ability to deep breathe and cough effectively. D. Apply oxygen at 10 L/minute via non-rebreather mask and monitor pulse oximeter may be necessary if there are signs of hypoxia. However, the vital sign changes here are more likely related to pain rather than respiratory distress, making pain management the immediate priority.