A patient presents with bilateral pitting edema and sleep apnea. What is the appropriate next diagnostic step?

The presence of bilateral pitting edema along with sleep apnea suggests potential cardiovascular involvement, particularly heart failure, as pulmonary congestion can lead to fluid retention and bilateral edema. An echocardiogram is the most appropriate next diagnostic step in this situation because it allows for direct assessment of the heart's function, structure, and any possible abnormalities such as left ventricular dysfunction, which could explain the patient's symptoms.

An echocardiogram can provide crucial information about ejection fraction, chamber sizes, and the presence of any valvular heart disease or other cardiac pathologies that might be contributing to the patient's symptoms. This data helps guide further management and treatment decisions effectively.

In comparison, a chest X-ray (CXR) can provide limited information and may not definitively assess cardiac function or structure. A CT scan of the chest can be useful for evaluating pulmonary conditions, but it is more invasive and less focused on cardiac evaluation than an echocardiogram. Blood gases analysis, while useful in assessing respiratory function, does not provide specific information about cardiac structure or function. Therefore, the echocardiogram is the most relevant and informative next step in this clinical scenario.