After two hours post coronary artery bypass surgery the client experienced a central venous pressure increasing from 13 mm Hg to 17 mm Hg within a half hour. The systolic blood pressure dropped to 90 mm Hg on inspiration and rose to 110 mm Hg on expiration. Heart sounds are distant upon auscultation, and decreased electrocardiogram (ECG) waveform amplitudes are assessed. Which is the cause of these clinical manifestations?