• Qi Liu, Yong-Hua Gao, Dong-Ming Hua, Wen Li, Zhe Cheng, Hui Zheng, and Rong-Chang Chen.
• 1 Department of Respiratory and Critical Medicine, the First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China ; 2 Respiratory Mechanics Lab, State Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Disease, Guangzhou Institute of Respiratory Disease, First Affiliated Hospital of Guangzhou Medical University, Guangzhou 510182, China ; 3 Department of Radiology, the First Affiliated Hospital of Guangzhou Medical University, Guangzhou 510182, China ; 4 Department of Radiology, the First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China.
• J Thorac Dis. 2015 Aug 1;7(8):1459-66.

BackgroundTraditionally, the choice of tidal volume for mechanical ventilation was based on body weight (BW) and usually, predicted BW was used to correct actual BW inter-individual variations in obesity and muscle weight. The method of selecting tidal volume depended on the fact that normal lung volumes, especially functional residual capacity (FRC), were mainly determined by height (indirectly by predicted BW), sex and age in healthy persons. However, FRCs in patients with acute respiratory distress syndrome (ARDS) might not abide by the same rule and be significantly different from each other in patients with the same height and sex. We hypothesized that FRC was determined by body length (surrogate for predicted BW) and age in healthy male beagle dogs but not in lung injured ones.MethodsA total of 24 dogs were recruited and ARDS model was induced by intravenous injection of oleic acid. FRC was measured by chest computer tomography. Blood gas analysis, extra vascular lung water and respiratory system mechanics were tested at baseline and post-lung injury. Age, body length and actual BW were also recorded before experiments.ResultsAfter lung injury, FRC decreased sharply from baseline (414±84) to (214±70) mL. For healthy lungs, FRC could be estimated by the following formula: FRC =21.86 × age (months) + 20.55 × body length (cm) - 1,337.98 (P<0.05), while for injured lungs, the formula of multiple linear regression was invalid (P=0.305).ConclusionsFRC was linearly related to body length in healthy dogs but not in lung injured ones. The traditional view of setting tidal volume based on predicted BW should be challenged cautiously.

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