Regional lung aeration and ventilation during pressure support and biphasic positive airway pressure ventilation in experimental lung injury

Abstract

IntroductionThere is an increasing interest in biphasic positive airway pressure with spontaneous breathing (BIPAP+SBmean), which is a combination of time-cycled controlled breaths at two levels of continuous positive airway pressure (BIPAP+SBcontrolled) and non-assisted spontaneous breathing (BIPAP+SBspont), in the early phase of acute lung injury (ALI). However, pressure support ventilation (PSV) remains the most commonly used mode of assisted ventilation. To date, the effects of BIPAP+SBmean and PSV on regional lung aeration and ventilation during ALI are only poorly defined.MethodsIn 10 anesthetized juvenile pigs, ALI was induced by surfactant depletion. BIPAP+SBmean and PSV were performed in a random sequence (1 h each) at comparable mean airway pressures and minute volumes. Gas exchange, hemodynamics, and inspiratory effort were determined and dynamic computed tomography scans obtained. Aeration and ventilation were calculated in four zones along the ventral-dorsal axis at lung apex, hilum and base.ResultsCompared to PSV, BIPAP+SBmean resulted in: 1) lower mean tidal volume, comparable oxygenation and hemodynamics, and increased PaCO2 and inspiratory effort; 2) less nonaerated areas at end-expiration; 3) decreased tidal hyperaeration and re-aeration; 4) similar distributions of ventilation. During BIPAP+SBmean: i) BIPAP+SBspont had lower tidal volumes and higher rates than BIPAP+SBcontrolled; ii) BIPAP+SBspont and BIPAP+SBcontrolled had similar distributions of ventilation and aeration; iii) BIPAP+SBcontrolled resulted in increased tidal re-aeration and hyperareation, compared to PSV. BIPAP+SBspont showed an opposite pattern.ConclusionsIn this model of ALI, the reduction of tidal re-aeration and hyperaeration during BIPAP+SBmean compared to PSV is not due to decreased nonaerated areas at end-expiration or different distribution of ventilation, but to lower tidal volumes during BIPAP+SBspont. The ratio between spontaneous to controlled breaths seems to play a pivotal role in reducing tidal re-aeration and hyperaeration during BIPAP+SBmean.

Associations between positive end-expiratory pressure and outcome of patients without ARDS at onset of ventilation: a systematic review and meta-analysis of randomized controlled trials

“…Atelectasis is more extensive in patients with the acute respiratory distress syndrome (ARDS) than in patients without lung injury and is more frequently seen with mandatory than spontaneous forms of ventilation [10, 11]. In patients with ARDS, therefore, the balance between prevention of atelectrauma and induction of overdistension could result in a net beneficial effect.…”

A fibre optic oxygen sensor that detects rapid PO2 changes under simulated conditions of cyclical atelectasis in vitro

“…These studies are new, but still employed a relatively slow oxygen sensing technology, and so no firm conclusions can be drawn as yet on the effect of elevated RRs on the amplitude of $P_{a_{{\text{O}}_2}}$ oscillations associated with cyclical atelectasis. A different explanation for $P_{a_{{\text{O}}_2}}$ oscillations that have the same period as breathing is related to regional aeration compartments and gas exchange in the lung, where pulmonary blood flow can cyclically be shifted from poorly to better ventilated regions in the lung (Gama de Abreu et al, 2010). …”

Experiences Using Airway Pressure Release Ventilation for Pneumonia with Severe Hypercapnia or Postoperative Pulmonary Edema

“…As described above, the APRV methodologies were subdivided into two categories: F-APRV; (Tables 1 and 3) and P-APRV (Tables 2 and 4). The majority of the animal studies (69 % of total) [2,4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] and human studies (82 % of total) [3, were in the F-APRV category.…”

“…1. Indeed, all of these mechanical breaths were defined as APRV [2][3][4][5]. As can be readily seen, the biggest difference between these APRV breaths is the duration at inspiration and expiration.…”