What should the nurse initially administer to a client who reports shortness of breath and chest pain after surgery?

In situations where a client presents with shortness of breath and chest pain, the priority is to ensure adequate oxygenation. Administering supplemental oxygen is crucial because it can quickly alleviate hypoxemia and improve oxygen delivery to the tissues, particularly in the post-operative setting where respiratory complications may arise.

By providing supplemental oxygen, the nurse addresses the immediate risk of inadequate oxygen levels, which can lead to further complications such as respiratory failure or cardiac ischemia. This intervention helps stabilize the client's condition, allowing for additional assessments, such as evaluating the underlying cause of symptoms and determining whether further treatments, like pain management or medications, are necessary.

The other options, while they may be indicated in certain contexts, do not address the immediate need for oxygenation. Intravenous morphine is used for pain relief but does not directly address the critical nature of potential hypoxia. Endotracheal intubation is an invasive procedure reserved for cases of severe respiratory failure or when airway protection is necessary, and sublingual nitroglycerin would be more appropriate for chest pain related to angina rather than initial management for shortness of breath after surgery.