The pathophysiology of atypical tamponade in infants undergoing cardiac surgery

Abstract

A small solid state transducer was used to measure pericardial pressure(PP) in 13 pediatric patients (mean age 18 months) at hourly intervals for24 h following cardiac surgery. The mean PP following closed cardiacsurgery via a left thoracotomy (group 1: 5 patients) was 2.7 +/- 1.4 mmHgand did not change with time. Maximum PP occurred during isovolumicrelaxation of the ventricle rising to a peak at the onset of the 'a' waveof 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, Pless 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). PPwas significantly raised in the 2 patients undergoing transventricularcorrection of Fallot's tetralogy (group 3, PP = 10.2 +/- 3.2 mmHg; group 3vs group 2, P less than 0.001) and in the 3 patients undergoing homograftconduit reconstruction of the right ventricular outflow tract for truncusarteriosus (group 4, PP = 9.3 +/- 2.6 mmHg; group 4 vs group 2, P less than0.001). The results confirm that PP is a mathematical function of theexpansile forces of the heart and the restricting forces of the pericardiumand mediastinum. Patients with pulmonary regurgitation or pulmonaryhypertensive crisis leading to increased right ventricular end diastolicdimension or a space occupying conduit have a high PP and are therefore atrisk of atypical tamponade. In this situation splinting open the chest mayreduce PP and break the cycle of falling cardiac output.