Estimation of shunt fraction by transesophageal echocardiography during one-lung ventilation

As the blood flow volume in non-dependent lung composed the primary part of the intrapulmonary shunt during one-lung ventilation (OLV), the shunt fraction (SF) during OLV can be represented by the ratio of blood flow volume in non-dependent lung to the bilateral lung. The purpose of this study is to estimate the shunt in non-dependent lung by transesophageal echocardiography (TEE). Fifteen adult patients requiring OLV for thoracic surgery were enrolled in the study. The upper pulmonary venous flow pattern in bilateral lung and main pulmonary artery flow pattern were acquired respectively by TEE for their velocity time integral (VTI) measurements in following time intervals: before OLV (T₀), 30 min after OLV (T₃₀) and 60 min after OLV (T₆₀). Simultaneously the arterial blood was sampled for gas analysis. SF was calculated by VTI of bilateral upper pulmonary veins, and percentage change of blood flow (BFP) was the ratio of upper pulmonary venous VTI between in OLV period and before OLV in non-dependent lung. There was significant decrease in PaO₂ and increase in cardiac output after OLV. The pulmonary blood flow in non-dependent lung decreased significantly compared with T₀, and SF was 37.1 ± 8.3 and 35.2 ± 7.2 % respectively at T₃₀ and T₆₀. There was significant liner correlation between SF and PaO₂ (r = 0.717), and between BFP and PaO₂ (r = 0.593). It is feasible to estimate intrapulmonary shunt by TEE in anesthetized patients undergoing OLV. SF measured by TEE has significant correlation with PaO₂, and it would expected to be used to predict hypoxemia during OLV.