The effects of low tidal ventilation on lung strain correlate with respiratory system compliance.
The effect of alterations in tidal volume on mortality of acute respiratory distress syndrome (ARDS) is determined by respiratory system compliance. We aimed to investigate the effects of different tidal volumes on lung strain in ARDS patients who had various levels of respiratory system compliance.



Nineteen patients were divided into high (Chighgroup) and low (Clowgroup) respiratory system compliance groups based on their respiratory system compliance values. We defined compliance ≥0.6 ml/(cmH2O/kg) as Chighand compliance <0.6 ml/(cmH2O/kg) as Clow. End-expiratory lung volumes (EELV) at various tidal volumes were measured by nitrogen wash-in/washout. Lung strain was calculated as the ratio between tidal volume and EELV. The primary outcome was that lung strain is a function of tidal volume in patients with various levels of respiratory system compliance.



The mean baseline EELV, strain and respiratory system compliance values were 1873 ml, 0.31 and 0.65 ml/(cmH2O/kg), respectively; differences in all of these parameters were statistically significant between the two groups. For all participants, a positive correlation was found between the respiratory system compliance and EELV (R = 0.488, p = 0.034). Driving pressure and strain increased together as the tidal volume increased from 6 ml/kg predicted body weight (PBW) to 12 ml/kg PBW. Compared to the ChighARDS patients, the driving pressure was significantly higher in the Clowpatients at each tidal volume. Similar effects of lung strain were found for tidal volumes of 6 and 8 ml/kg PBW. The "lung injury" limits for driving pressure and lung strain were much easier to exceed with increases in the tidal volume in Clowpatients.



Respiratory system compliance affected the relationships between tidal volume and driving pressure and lung strain in ARDS patients. These results showed that increasing tidal volume induced lung injury more easily in patients with low respiratory system compliance.



Clinicaltrials.gov identifier NCT01864668 , Registered 21 May 2013.
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Jianfeng
J
Xie
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Fang
F
Jin
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Chun
C
Pan
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Songqiao
S
Liu
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Ling
L
Liu
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Jingyuan
J
Xu
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China.
Yi
Y
Yang
Department of Critical Care Medicine, Nanjing ZhongDa Hospital, School of Medicine, Southeast University, 87 Dingjiaqiao Road, Gulou District, Nanjing, Jiangsu, 210009, China. haiboq2000@163.com.
Haibo
H
Qiu
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008170:Lung Compliance; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000401:mortality / Q000503:physiopathology / Q000628:therapy*; D013990:Tidal Volume / Q000502:physiology*
Acute respiratory distress syndrome; Lung strain; Mechanical ventilation; Tidal volume; Ventilator-induced lung injury