Abstract
BackgroundPreservation of spontaneous breathing (SB) is sometimes debated because it has potentially both negative and positive effects on lung injury in comparison with fully controlled mechanical ventilation (CMV). We wanted (1) to verify in mechanically ventilated patients if the change in transpulmonary pressure was similar between pressure support ventilation (PSV) and CMV for a similar tidal volume, (2) to estimate the influence of SB on alveolar pressure (Palv), and (3) to determine whether a reliable plateau pressure could be measured during pressure support ventilation (PSV).MethodsWe studied ten patients equipped with esophageal catheters undergoing three levels of PSV followed by a phase of CMV. For each condition, we calculated the maximal and mean transpulmonary (ΔPL) swings and Palv.ResultsOverall, ΔPL was similar between CMV and PSV, but only loosely correlated. The differences in ΔPL between CMV and PSV were explained largely by different inspiratory flows, indicating that the resistive pressure drop caused this difference. By contrast, the Palv profile was very different between CMV and SB; SB led to progressively more negative Palv during inspiration, and Palv became lower than the set positive end-expiratory pressure in nine of ten patients at low PSV. Finally, inspiratory occlusion holds performed during PSV led to plateau and Δ PL pressures comparable with those measured during CMV.ConclusionsUnder similar conditions of flow and volume, transpulmonary pressure change is similar between CMV and PSV. SB during mechanical ventilation can cause remarkably negative swings in Palv, a mechanism by which SB might potentially induce lung injury.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-016-1290-9) contains supplementary material, which is available to authorized users.
Highlights
Preservation of spontaneous breathing (SB) is sometimes debated because it has potentially both negative and positive effects on lung injury in comparison with fully controlled mechanical ventilation (CMV)
We evaluated the reliability of the measurement of plateau pressure (Pplat) during pressure support ventilation (PSV) compared with that obtained during CMV
We enrolled patients admitted to our general intensive care unit who were orotracheally intubated and undergoing PSV or neurally adjusted ventilatory assist with a positive end-expiratory pressure (PEEP) level greater than 5 cmH2O
Summary
Preservation of spontaneous breathing (SB) is sometimes debated because it has potentially both negative and positive effects on lung injury in comparison with fully controlled mechanical ventilation (CMV). The total PL can be divided into the pressure generated to overcome the resistance to airflow between the airway opening and the alveoli, and the pressure needed to expand the terminal airways (i.e., the transalveolar pressure). The latter part of the PL, which equals the product of lung elastance and volume, is dissipated across the alveolus and is commonly considered to cause VILI [17]. Airflow generation in the presence of elevated airflow resistance may lead to an extremely high PL during both fully controlled and spontaneously assisted ventilation, but accompanied in the latter case by very negative pressure around and even inside the alveoli
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