What ABG result is expected for a patient with an acute on chronic episode of COPD?

In a patient experiencing an acute on chronic episode of Chronic Obstructive Pulmonary Disease (COPD), the typical arterial blood gas (ABG) results reflect a combination of respiratory acidosis due to hypoventilation and carbon dioxide retention, as well as potential metabolic compensation.

The expected ABG result indicated in the correct choice shows a pH of 7.48, which is slightly elevated (alkalosis), with a PaCO2 of 50 mm Hg that suggests that carbon dioxide levels are starting to rise and the patient is not adequately ventilating, but this does not fully lead to significant respiratory acidosis at this stage. The PaO2 of 51 mm Hg indicates that the patient is experiencing hypoxemia, which can occur during an exacerbation of COPD. The HCO3- level of 34 mEq/L suggests that there is some metabolic compensation happening, as the kidneys may be retaining bicarbonate to buffer the acidosis.

This picture can be typical in those patients who have chronic respiratory acidosis and are undergoing an acute exacerbation, where the elevated HCO3- reflects chronic compensation and the pH still being relatively normal or mildly elevated due to mixed acid-base disorders.

In contrast, other given options