Changes in Functional Residual Capacity and Lung Mechanics during Surgical Repair of Congenital Heart Diseases

Abstract

Background To characterize the impact of lung volume changes in the lung function impairment after the surgical repair of congenital heart diseases, combined measurements of functional residual capacity, lung clearance index, and respiratory mechanics were performed in children with hypoperfused lungs (tetralogy of Fallot [TOF]) or with pulmonary hyperperfusion (ventricular septal defect [VSD]). Methods Lung volume and clearance were assessed by using a sulfur hexafluoride washout technique, and the mechanical properties of the respiratory system were assessed using a low-frequency oscillation technique. Lung volume and oscillatory measurements were made preoperatively, before and after cardiopulmonary bypass and aortic clamping (AC), and after chest closure. Results Impairments in airway (36 +/- 2%) and tissue mechanics (22 +/- 3%) were observed in the children with TOF after bypass; AC and chest closure were associated with marked decreases in functional residual capacity (-24 +/- 3% and -13 +/- 2% for TOF and VSD after AC, respectively) and increases in lung clearance index (-60 +/- 6% and -24 +/- 3% for TOF and VSD after AC, respectively). Smaller impairments in lung mechanics were observed after bypass and AC in children with VSD. Conclusions These findings suggest that the lung volume loss and lung mechanical deteriorations are probably caused by a diminished tethering effect of the lung periphery through a reduced filling of the pulmonary capillaries. This effect seems to be more pronounced in children with hypoperfused lungs (TOF) than in those with pulmonary hyperperfusion (VSD). The beneficial postoperative changes in children with VSD are consequences of the reversal of the pulmonary vascular engorgement after surgical repair.