Following initiation of oxygen therapy in a patient with COPD, which parameter should be continuously monitored?

Chronic obstructive pulmonary disease involves airflow limitation, ventilation-perfusion mismatch, and potential CO2 retention, especially during oxygen therapy due to altered hypoxic respiratory drive and worsening hypercapnia from increased dead space ventilation and Haldane effect-related changes in gas exchange. Rationale: A. Blood pressure monitoring is important in overall hemodynamic assessment but does not directly reflect adequacy of ventilation or gas exchange in COPD patients receiving oxygen therapy. It is not the primary parameter for oxygen therapy monitoring. B. Arterial blood gas (ABG) levels provide direct measurement of oxygenation (PaO2), ventilation (PaCO2), and acid-base status. In COPD patients, oxygen therapy can lead to hypercapnia and respiratory acidosis, making ABGs the most critical parameter for continuous evaluation. C. Heart rate may reflect general physiologic stress or hypoxia but is non-specific and does not accurately assess ventilatory effectiveness or CO2 retention during oxygen therapy. D. Tidal volume reflects ventilatory mechanics but is not routinely or continuously measured in standard nursing care compared to ABGs. It provides limited information about gas exchange status in COPD management.