Abstract
BackgroundThe 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.MethodsNineteen patients were divided into high (Chigh group) and low (Clow group) respiratory system compliance groups based on their respiratory system compliance values. We defined compliance ≥0.6 ml/(cmH2O/kg) as Chigh and 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.ResultsThe 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 Chigh ARDS patients, the driving pressure was significantly higher in the Clow patients 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 Clow patients.ConclusionsRespiratory 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.Trial registrationClinicaltrials.gov identifier NCT01864668, Registered 21 May 2013.
Highlights
The effect of alterations in tidal volume on mortality of acute respiratory distress syndrome (ARDS) is determined by respiratory system compliance
Our study found that respiratory system compliance affected the relationship between tidal volume and strain in ARDS patients
We found that in the patients with low respiratory system compliance, the driving pressure and lung strain could exceed the safe thresholds, even when using a tidal volume of 6 ml/kg predicted body weight (PBW) (Figs. 2 and 3)
Summary
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. Mechanical ventilation is an established intervention in the supportive management of patients with acute respiratory distress syndrome (ARDS) [1]. Protti et al found that there was a safe lung strain threshold during mechanical ventilation [9]. A recent study reported that patients with higher strain values showed fourfold increases in the interleukin (IL) and IL-8 concentrations in their bronchoalveolar lavage fluid that were associated with aggravated lung injury [11]. Strain has been applied to titrate the positive end-expiratory pressure (PEEP) and tidal volume settings [12, 13]
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