Determination of the side-separated pulmonary right-toleft shunt volume

Background :With the present method of intrapulmonary right-to-left shunt volume calculation, no differentiation can be made between the shunt volume shares of the right and left lungs. For a better understanding of pathophysiological processes during thorax surgery with side-separated ventilation, a side-separated shunt volume determination would be useful. Materials and Methods : In 14 young female pigs, catheters were implanted into the left atrium after left thoracotomy. After transient clamping of the ipsilateral pulmonary veins, pulmonary venous blood was selectively obtained from the right lung. Cardiac output (CO) and side-separated pulmonary perfusion were determined with flowprobes at the pulmonary trunk and the left pulmonary artery. The shunt volumes were determined before and after thoracotomy during two-lung ventilation (Two-LV), after one-lung (right) ventilation (One-LV) with a continuous positive airway pressure (CPAP) of +7.5, +5.0 cm H2O, and under atelectasis of the non-dependent left lung (NDL). Results : After thoracotomy in lateral decubitus position and Two-LV, the shunt volumes of the two lungs differ. The right lung holds the major share (11.0±1.7%CO) [mean±SD]. The share of the left NDL is only 3.3±1.4. Under One-LV (right) and CPAP in the NDL, the total pulmonary shunt volume rises. This is caused by the increase in the NDL shunt volume share to 8.8±5.2 under CPAP +7.5 (p<0.05) and to 9.7±2.5 under CPAP +5.0 (p<0.05). Conclusions : The new intraoperative method of side-separated arterial blood gas analysis in conjunction with side-separated perfusion measurement makes side- separated rightto- left shunt volume determination possible and may lead to interesting new pathophysiological insights.