Weight and Abdominal Girth Predict Tidal Volume Requirement During Mechanical Ventilation for General Anaesthesia: A Cross-sectional Study

Abstract

Background: Evidence that tidal volume (TV) is related to age, height, weight, chest circumference, and abdominal girth exists. However, it is unclear which of these has the strongest association with TV. This study aimed to investigate the main factors associated with TV and determine a method for accurately predicting TV requirement during mechanical ventilation. Methods: From December 2019 to January 2021, we enrolled 133 patients who were scheduled for surgery. Their age, height, weight, abdominal girth, and chest circumference were recorded. Intraoperatively, at 30 minutes after mechanical ventilation during general anaesthesia, the TV was increased or decreased by 25 ml if the partial pressure of carbon dioxide (PaCO2) was > 45 mmHg or < 35 mmHg, respectively. This was continued until we observed two consecutive PaCO2 values between 35 and 45 mmHg. The TV setting was recorded at this point. Linear regression and multiple regression analyses were performed. Results: The data of 100 patients were analysed. Linear regression analysis showed significant univariate correlations between age, weight, height, abdominal girth, chest circumference, and TV requirement. (all P ≤ 0.049). Multiple linear regression analysis showed that weight and abdominal girth were key determinants of TV requirement (both P < 0.001). The adjusted R2 for the regression equation was 0.813. The regression equation for accurately predicting TV requirement was Y = 312 + 5.717X1 - 2.798X2 (Y, TV requirement; X1, weight; and X2, abdominal girth). Conclusion: TV requirement during mechanical ventilation for general anaesthesia can accurately be set based on weight and abdominal girth.