Do spontaneous and mechanical breathing have similar effects on average transpulmonary and alveolar pressure? A clinical crossover study

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.

Mechanical Ventilation to Minimize Progression of Lung Injury in Acute Respiratory Failure

“…2) Based on classical physiologic concepts, the transpulmonary pressure swings, i.e., the stress on the lungs, are similar for a given tidal volume (starting at the same lung volume), whether generated by a mechanical ventilator, spontaneous effort, both or negative pressure ventilation (13,14), as illustrated in figure 1. However, there are several subtleties that can lead to lung injury in patients with injured lungs, related to the regional distribution of injury, with associated differences in local transpulmonary pressures and local stress (10,15).…”

Ventilation-induced lung injury exists in spontaneously breathing patients with acute respiratory failure: Yes

“…In a series of patients submitted to different levels of pressure support and to controlled mechanical ventilation, and in whom transpulmonary pressure was measured as airway minus esophageal pressure, Bellani et al checked that this assumption held true [15]. Indeed, when breaths were matched to have the same volume and flow, transpulmonary swings were identical whatever the modality of ventilation.…”

Protecting lungs during spontaneous breathing: what can we do?

“…This was supposed to be hold during both passive ventilation and spontaneous breathing. Indeed, Bellani and his colleagues demonstrated that if the volume and flow are comparable, the tidal change in transpulmonary pressure is similar between passive ventilation and spontaneous breathing (17).…”