The use of continuous pulmonary artery monitoring system and the analysis of pulmonary artery wave contour after open heart sugery in children

The evaluate hemodynamics of pulmonary circulation after open heart surgery, an analysis of pulmonary artery wave contour using the Windkessel model was performed in 97 children with ventricular septal defect (VSD), tetralogy of Fallot (TF), total anomalous pulmonary venous connection (TAPVC), and transposition of the great artery with large VSD (TGA with VSD). Various parameters used for the analysis were mean pulmonary artery pressure, pulmonary to systemic pressure ratio (Pp/Ps), pulmonary vascular resistance, time constant (TC) and compliance (C). Cardiac output was measured by dye dilution methods. The patients were divided into 3 groups: 1) VSD PH group;26 patients with VSD and pulmonary hypertension (PH), 2) TF group;25 patients with TF, 3) VSD group;29 patients with ventricular septal defect without pulmonary hypertension. In addition to these 3 groups, separate analysis was also carried out on so called PH group which consisted of 12 patients with TAPVC, 2 patients with TGA and 26 patients with VSD PH. Early Postoperative Pp/Ps in VSD PH group and TF group were significantly higher than that in VSD group. TC at 6 hours after the termination of cardiopulmonary bypass was lower (P<0.05) in TF group than that in VSD PH and VSD group. In TF group, there was a weak correlation between postoperative C and postoperative Pp/Ps (r=-0.383) In VSD PH group, there was a weak correlation between TC and postoperative Pp/Ps (r=0.471) Five patients in PH group demonstrated an acute elevation of Pp/Ps (>0.5) upon withdrawal from mechanical ventilation despite of low Pp/Ps in the early postoperative period. The TC and C in these 5 patients were characteristically discriminated from others by showing the value lower than 0.14 and 0.8, respectively. It is concluded that 1) TC and C may represent the difference in the mechanism of development of pulmonary hypertension and 2) these two parameters could be useful indicators to predict acute elevation of pulmonary vascular resistance which may take place at the time of weaning from mechanica:l ventilation.