To evaluate the effectiveness of prescribed therapies for a patient with ventilatory failure, which diagnostic test will be most useful to the nurse?

A. Pulse oximetry: Pulse oximetry provides continuous monitoring of oxygen saturation but does not measure carbon dioxide levels or acid-base status. In ventilatory failure, hypoventilation can cause hypercapnia even if oxygen saturation is normal, making pulse oximetry insufficient for full assessment. B. Chest x-rays: Chest x-rays can identify structural lung changes, infiltrates, or complications such as pneumothorax, but they do not provide real-time information about gas exchange or the effectiveness of ventilatory support. C. Pulmonary artery pressure monitoring: Pulmonary artery catheters assess cardiac output and pulmonary pressures, which may be helpful in some critically ill patients, but they do not directly measure ventilation or gas exchange, which are central to evaluating ventilatory failure. D. Arterial blood gas (ABG) analysis: ABGs provide direct measurement of PaO₂, PaCO₂, and pH, offering critical information about oxygenation, ventilation, and acid-base balance. These parameters are essential for determining the effectiveness of therapies such as mechanical ventilation, supplemental oxygen, or pharmacologic interventions in patients with ventilatory failure.