Abstract
BackgroundLung-protective ventilation strategy suggests the use of low tidal volume, depending on ideal body weight, and adequate levels of PEEP. However, reducing tidal volume according to ideal body weight does not always prevent overstress and overstrain. On the contrary, titrating mechanical ventilation on airway driving pressure, computed as airway pressure changes from PEEP to end-inspiratory plateau pressure, equivalent to the ratio between the tidal volume and compliance of respiratory system, should better reflect lung injury. However, possible changes in chest wall elastance could affect the reliability of airway driving pressure. The aim of this study was to evaluate if airway driving pressure could accurately predict lung stress (the pressure generated into the lung due to PEEP and tidal volume).MethodsOne hundred and fifty ARDS patients were enrolled. At 5 and 15 cmH2O of PEEP, lung stress, driving pressure, lung and chest wall elastance were measured.ResultsThe applied tidal volume (mL/kg of ideal body weight) was not related to lung gas volume (r2 = 0.0005 p = 0.772). Patients were divided according to an airway driving pressure lower and equal/higher than 15 cmH2O (the lower and higher airway driving pressure groups). At both PEEP levels, the higher airway driving pressure group had a significantly higher lung stress, respiratory system and lung elastance compared to the lower airway driving pressure group. Airway driving pressure was significantly related to lung stress (r2 = 0.581 p < 0.0001 and r2 = 0.353 p < 0.0001 at 5 and 15 cmH2O of PEEP). For a lung stress of 24 and 26 cmH2O, the optimal cutoff value for the airway driving pressure were 15.0 cmH2O (ROC AUC 0.85, 95 % CI = 0.782–0.922); and 16.7 (ROC AUC 0.84, 95 % CI = 0.742–0.936).ConclusionsAirway driving pressure can detect lung overstress with an acceptable accuracy. However, further studies are needed to establish if these limits could be used for ventilator settings.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-016-1446-7) contains supplementary material, which is available to authorized users.
Highlights
Lung-protective ventilation strategy suggests the use of low tidal volume, depending on ideal body weight, and adequate levels of positive endexpiratory pressure (PEEP)
Trying to reduce overstress/ strain, the majority of the studies applied a tidal volume standardized to ideal body weight, computed according to the patient’s height and sex [37], as in healthy subjects the lung volume is related to height [38]
One possible solution should be to titrate the tidal volume according to the airway driving pressure, which depends on the respiratory system elastance, better reflecting the severity of the disease [3]
Summary
Lung-protective ventilation strategy suggests the use of low tidal volume, depending on ideal body weight, and adequate levels of PEEP. Lung-protective ventilation strategy, commonly employed for moderate to severe forms of acute respiratory distress syndrome (ARDS) [1], suggests the use of low tidal volume, set according to the ideal body weight of the patient (6 mL/kgIBW) [2], and higher levels of positive endexpiratory pressure (PEEP) to limit ventilator-induced lung injury (VILI) [2,3,4,5,6,7]. On the contrary, titrating the mechanical ventilation on the airway driving pressure, measured as the airway pressure changes from PEEP to end-inspiratory plateau pressure, equivalent to the ratio between the tidal volume and compliance of respiratory system, should better reflect the lung injury because in each patient the applied tidal volume is related to the available lung gas volume [11, 24]. The transpulmonary driving pressure (dynamic stress), taking into account the chest wall elastance, could better reflect lung stress
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