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: A low end-tidal CO₂ level typically reflects hyperventilation or poor perfusion rather than respiratory failure. In early respiratory failure, CO₂ levels usually rise as the client experiences hypoventilation and impaired gas exchange. B. Agitation: Agitation is an early sign of hypoxia as the brain becomes deprived of adequate oxygen. Clients often show restlessness, confusion, or behavioral changes before more obvious signs of respiratory failure appear, making this a critical early indicator. C. Xerostomia: Dry mouth is a nonspecific finding that may result from dehydration, medications, or mouth breathing but does not reliably indicate respiratory failure. It lacks the clinical significance needed to identify deterioration in oxygenation or ventilation. D. Friction rub: A friction rub suggests pleural inflammation rather than respiratory failure. While it may occur with some pulmonary conditions, it does not directly reflect the impaired oxygenation or ventilation associated with respiratory failure.