The pathophysiology of atypical tamponade in infants undergoing cardiac surgery.

A small solid state transducer was used to measure pericardial pressure (PP) in 13 pediatric patients (mean age 18 months) at hourly intervals for 24 h following cardiac surgery. The mean PP following closed cardiac surgery via a left thoracotomy (group 1: 5 patients) was 2.7 +/- 1.4 mmHg and did not change with time. Maximum PP occurred during isovolumic relaxation of the ventricle rising to a peak at the onset of the 'a' wave of the central venous pressure (CVP). PP was strongly correlated with CVP (r = 0.58, P less than 0.001) but not with airways pressure (r = 0.27, P less than 0.2). Mean PP in the 3 patients undergoing transatrial surgery (group 2) was 4.5 +/- 2.7 mmHg (group 1 vs group 2, P less than 0.001). PP was significantly raised in the 2 patients undergoing transventricular correction of Fallot's tetralogy (group 3, PP = 10.2 +/- 3.2 mmHg; group 3 vs group 2, P less than 0.001) and in the 3 patients undergoing homograft conduit reconstruction of the right ventricular outflow tract for truncus arteriosus (group 4, PP = 9.3 +/- 2.6 mmHg; group 4 vs group 2, P less than 0.001). The results confirm that PP is a mathematical function of the expansile forces of the heart and the restricting forces of the pericardium and mediastinum. Patients with pulmonary regurgitation or pulmonary hypertensive crisis leading to increased right ventricular end diastolic dimension or a space occupying conduit have a high PP and are therefore at risk of atypical tamponade. In this situation splinting open the chest may reduce PP and break the cycle of falling cardiac output.