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

Assessment of a client with potential respiratory failure involves identifying early signs of inadequate oxygenation and ventilation. Respiratory failure occurs when the lungs cannot effectively oxygenate blood or remove carbon dioxide, leading to hypoxemia, hypercapnia, and impaired tissue perfusion. Early recognition is critical because neurologic changes often appear before complete decompensation. Monitoring mental status, respiratory pattern, and oxygenation helps guide timely intervention. Rationale: A. A friction rub is typically associated with pleural inflammation such as pleuritis and is not a direct indicator of respiratory failure. It results from inflamed pleural surfaces rubbing together during respiration. While it may indicate an underlying pulmonary condition, it does not specifically reflect impaired gas exchange or ventilatory failure. B. Decreased end-tidal CO₂ may occur in certain conditions such as hyperventilation or reduced cardiac output, but it is not a primary or reliable standalone indicator of respiratory failure. In respiratory failure, CO₂ levels are more commonly elevated due to hypoventilation. C. Xerostomia (dry mouth) is not related to respiratory failure and is more commonly associated with dehydration, medication side effects, or chronic conditions affecting salivary glands. It does not reflect oxygenation or ventilation status. Therefore, it is not a clinically significant indicator of respiratory compromise. D. Agitation is an early neurologic sign of hypoxemia or hypercapnia and can indicate developing respiratory failure. As oxygen delivery to the brain decreases or carbon dioxide levels rise, the client may become restless, confused, or anxious. These behavioral changes often precede more severe manifestations such as decreased consciousness or respiratory arrest, making it an important early warning sign.