Increased alveolar deadspace after closure of cardiac septal defects: pulmonary air embolism or failure of homeostasis?

During surgery for closure of atrial or ventricular septal defects (ASD, VSD), we used a computerized on-line system to follow changes in the alveolar deadspace fraction. We observed a large increase in the alveolar deadspace immediately following septal defect closure. No increase had been observed post-cardio-pulmonary bypass in children operated upon because of aortic or pulmonary stenosis, or in adults undergoing myocardial revascularization. The increase in deadspace is probably a result of the lung's failure to adjust to the large decrease in pulmonary blood flow following septal defect closure. An alternative cause for the finding, that of pulmonary artery air embolism occurring intraoperatively, appears to be less likely.