The nurse administers ambrisentan to the client with pulmonary arterial hypertension. What assessment should the nurse prioritize in order to monitor the effectiveness of this medication?

A. Assess the client's oxygen saturation: Oxygen saturation is important, but it is not the best measure of ambrisentan's effectiveness, which is focused on improving exercise capacity and symptoms related to pulmonary arterial hypertension. B. Check the client's blood pressure lying, sitting, and standing: Blood pressure monitoring is important, but ambrisentan's primary goal is to improve exercise tolerance and reduce symptoms, so this is less relevant for assessing effectiveness. C. Determine the client's exercise tolerance: Ambrisentan improves exercise capacity and reduces symptoms of pulmonary arterial hypertension. Assessing exercise tolerance directly evaluates the medication's effectiveness in improving functional status. D. Auscultate the client's lungs: While lung auscultation is helpful, ambrisentan targets pulmonary arterial hypertension, not lung sounds. Exercise tolerance is the best assessment for its effectiveness.