Improvement of PaO2 during one-lung ventilation with partial left-heart bypass in pediatric patients is caused by increased blood flow to the dependent lung

摘要

LEFT-HEART BYPASS (LHB) removes a portion of oxygenated pulmonary venous blood from the left atrium for delivery to a distal aortic site or the femoral artery. Partial LHB is often used in thoracoabdominal aneurysm repair in adults,1 whereas aortic coarctation surgery is a main indication in the pediatric population.2 The advantages of this technique when using a centrifugal pump without a venous reservoir or an oxygenator/heat exchanger include a reduction in left ventricular afterload and continuous distal aortic perfusion, which potentially reduces renal, splanchnic, and spinal cord ischemic times.3 Another potential advantage of partial LHB is the improvement of arterial partial pressure of oxygen (PaO2) during one-lung ventilation (OLV) as has been shown in adults undergoing thoracoabdominal aneurysm repair.4 Two cases in children are described in which LHB during OLV substantially improved PaO2. The authors postulate that decompression of the left atrium during partial LHB and OLV increases the proportion of total pulmonary blood delivered to the dependent lung by increasing the gradient between the pulmonary arterial and venous pressures in the dependent lung. In addition, the mathematic modeling to explain the physiology responsible for this finding is presented.