Four hours post-CABG, a patient is receiving supplemental oxygen through a nasal cannula at 2 L/min. What is the most appropriate method for evaluating the patient's response to oxygen therapy?

The most appropriate method for evaluating the patient's response to oxygen therapy is measuring the SpO2 (oxygen saturation). This non-invasive method provides an immediate and continuous assessment of the patient's oxygen levels, allowing healthcare providers to determine whether the supplemental oxygen is effectively increasing the amount of oxygen in the patient's bloodstream.

Using a pulse oximeter to measure SpO2 is particularly relevant in the context of post-CABG patients, as it can quickly indicate how well oxygen is being delivered and utilized by the body without the need for arterial blood samples. Furthermore, maintaining adequate oxygenation is critical after major surgery, and the SpO2 reading can help guide further interventions if needed.

While evaluating the patient for respiratory distress and observing for cyanosis can provide additional clinical information, these assessments are more subjective and not as precise as measuring SpO2. Arterial blood gas (ABG) analysis, while reliable, is more invasive and would not be the immediate or practical choice in a stable post-operative patient when a non-invasive option is readily available. Thus, measuring SpO2 is the most effective approach for monitoring oxygen therapy in this situation.