Volume of Tidal Gas Movement in the Nonventilated Lung during One-lung Ventilation and its Relevant Factors

Abstract Background: The passive ventilation of nonventilated lung results in tidal gas movement (TGM) and thus affects lung collapse. The present study aimed to measure the volume of TGM and to analyse the relevant factors of the TGM index (TGM/body surface area). Methods: One hundred eight patients scheduled for elective thoracoscopic surgeries were enrolled. Lung isolation was achieved with a double-lumen endobronchial tube (DLT). The paediatric spirometry sensor was connected to the double-lumen connector of the nonventilated lung to measure the volume of TGM during one-lung ventilation (OLV) in the lateral position. The TGM index was calculated. The multiple linear regression was analysed using the TGM index as the dependent variables. Independent variables were also recorded: 1) age, sex, body mass index (BMI); 2) forced vital capacity (FVC), FEV1/FVC, minute ventilation volume (MVV); 3) dynamic lung compliance (Cdyn) and peak inspiratory pressure (PIP) during dual lung ventilation; 4) the side of OLV; and 5) whether lung puncture for localization of the pulmonary nodule was performed on the day of surgery. The oxygen concentration in the nonventilated lung was measured at 5 min after OLV, and its correlation with the TGM index was analysed. Results: The volume of TGM in the nonventilated lung during OLV was 78 [37] mL. The TGM index was 45 [20] mL/m2 and was negatively correlated with the oxygen concentration in the nonventilated lung at 5 min after OLV. The multiple linear regression model for the TGM index was deduced as follows: TGM index (mL/m2)=C+12.770×a-3.987×b-1.237×c-2.664×d, where C is a constant 95.621 mL/m2, a is 1 for males and 0 for females, b is 1 for right OLV and 0 for left OLV, c is BMI (kg/m2), and d is PIP (cmH2O). Conclusions: The TGM index is negatively correlated with the oxygen concentration of the nonventilated lung at 5 min after OLV. Sex, side of OLV, BMI and PIP are independently correlated with the TGM index.Trial registration: This study was registered at ChiCTR (www.chictr.org.cn, ChiCTR1900024220) on July 1, 2019.Key Words: tidal gas movement, TGM index, one-lung ventilation, lung collapse, double-lumen endobronchial tube, dynamic lung compliance, thoracoscopy