A nurse is assessing a client. Which of the following findings should the nurse identify as an indication of respiratory failure?

A. Decreased end-tidal CO2 (ETCO₂) typically indicates hyperventilation, low cardiac output, or decreased perfusion. While it reflects changes in ventilation and perfusion, it is not a reliable early indicator of respiratory failure. Respiratory failure is often associated with hypoventilation and hypercapnia (elevated CO₂), especially in cases of ventilatory failure, making low ETCO₂ misleading in this context. B. Xerostomia, or dry mouth, is a common symptom related to dehydration, medication side effects, or mouth breathing, and does not reflect respiratory compromise or failure. C. Agitation is an early neurologic manifestation of hypoxemia, which can indicate impending respiratory failure. Hypoxemia reduces oxygen delivery to the brain, leading to restlessness, confusion, irritability, or anxiety. Recognizing these early signs allows for prompt assessment and intervention, such as administering supplemental oxygen, supporting ventilation, or addressing the underlying cause of respiratory compromise, to prevent progression to respiratory arrest. D. A pleural friction rub is a physical finding caused by inflammation of the pleura, as seen in pleuritis, pneumonia, or pulmonary embolism, but it does not indicate inadequate gas exchange or respiratory failure. It is a localized lung sound rather than a systemic sign of hypoxemia or hypercapnia.