Outcomes of Patients Presenting with Mild Acute Respiratory Distress Syndrome

Abstract

T HE Berlin definition of acute respiratory distress syndrome (ARDS) categorizes patients with partial pressure of arterial blood oxygen content to inspired fraction of oxygen (PaO 2 /fraction of inspired oxygen [FIO 2 ]) ranging from 200 to 300 mmHg as "mild ARDS." 1 In the preceding American European Consensus Conference, this population was defined as having "non-ARDS acute lung injury." 2 Some clinicians continue to overlook these less severely hypoxemic patients and instead pay closer attention to patients they consider to have "actual" ARDS (i.e., moderate and severe ARDS groups). This group has not been included in some recent studies recruiting patients with ARDS. 3-6 Patients Editor's Perspective What We Already Know about This Topic • Hospital mortality in acute respiratory distress syndrome is approximately 40%, but mortality and trajectory in "mild" acute respiratory distress syndrome (classified only since 2012) are unknown, and many cases are not detected What This Article Tells Us That Is New • Approximately 80% of cases of mild acute respiratory distress syndrome persist or worsen in the first week; in all cases, the mortality is substantial (30%) and is higher (37%) in those in whom the acute respiratory distress syndrome progresses

Prevention and treatment of acute lung injury with time-controlled adaptive ventilation: physiologically informed modification of airway pressure release ventilation

“…The ARDSnet Low Vt (LVt) method is intended to protect the non-dependent normal lung tissue from overdistension (OD) and reduce alveolar recruitment/ derecruitment (R/D) with positive end expiratory pressure (PEEP), while resting severely injured tissue by allowing it to remain collapsed throughout the ventilation cycle [2]. However, this strategy has not further reduced ARDS mortality [1,[3][4][5][6][7][8][9][10][11]. This suggests that our understanding of ARDS pathophysiology remains [12] all using the airway pressure release ventilation (APRV) mode but with different methods: a Stock et al used a CPAP phase that encompassed 60% of each breath, a release phase of 1.27 s and a respiratory rate (RR) of 20/min [98]; b Davis et al decreased the respiratory rate by prolonging both the CPAP and release phase [99]; c Gama de Abreau et al adjusted their CPAP and release phase to values typical of a conventional breath [100]; d Roy et al minimized the release phase and extended CPAP to occupy 90% of each breath, typical of the time-controlled adaptive ventilation (TCAV) method [83].…”

“…The current understanding is that open and collapsed tissues are not delineated into compartments, but are rather intermingled throughout the entire lung [17][18][19][20][21]. The unchanged mortality associated with the LVt method may also reflect the fact that maintaining lung tissue collapse ("resting") may not be protective [1,[3][4][5][6][7][8][9][10][11]. The atelectatic lung does not exchange gas, is susceptible to pneumonia, and may ultimately lead to collapse induration and fibrosis with the inability to re-inflate or epithelialize the airspace [22][23][24].…”

“…Current ARDS treatment is supportive: protective mechanical ventilation, typically using lower tidal volume ventilation (Vt) and low-moderate positive end expiratory pressure (PEEP) [2]. Unfortunately, current protective ventilation strategies have not lessened ARDS mortality rate [1,[3][4][5][6][7][8][9][10][11]. The determinant of VILI is not the "mode" of ventilation, but the way parameters of the mechanical breath are set and combined.…”

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

“…These methods include using dead space, lung stress and strain, lung compliance, CT, pressure-volume curve inflection points, and electrical impedance tomography, but there is no current bedside technique to determine whether the set PEEP has actually stabilized the lung (Nieman et al, 2017a). The above problems with the ARDSnet protect, rest, and stabilize method may partially explain the lack of improved outcome in ARDS mortality over the last 20 years (Figure 1) (Brun-Buisson et al, 2004;Phua et al, 2009;Villar et al, 2011;Caser et al, 2014;Bellani et al, 2016;Laffey et al, 2016;Villar et al, 2016;Maca et al, 2017;Raymondos et al, 2017;Rezoagli et al, 2017;Fan et al, 2018;McNicholas et al, 2018;Pham et al, 2019). By allowing the lung to remain heterogeneously collapsed, the protect, rest, and stabilize method is unintendedly preserving the constraints of ventilating the heterogeneously injured lung, which is nearly impossible to do without causing some degree of VILI.…”

“…It was not until the ARDS Network (ARDSnet) conducted the seminal ARMA study, published in 2000, that a reduction in mortality was shown (Acute Respiratory Distress Syndrome Network, 2000). However, most (Phua et al, 2009;Villar et al, 2011;Caser et al, 2014;Bellani et al, 2016;Laffey et al, 2016;Villar et al, 2016;Maca et al, 2017;Raymondos et al, 2017;Rezoagli et al, 2017;Fan et al, 2018;McNicholas et al, 2018;Pham et al, 2019;Shen et al, 2019) but not all (Brun-Buisson et al, 2004;Fan et al, 2005;Putensen et al, 2009;Petrucci and De Feo, 2013;Shen et al, 2019) of the recent statistical-and meta-analyses have shown that ARDS mortality has not been reduced below the 31% "gold standard" of the 2000 ARMA study but rather remains unacceptably high at ∼40% (Figure 1). Despite these disappointing results, the low-Vt ARDSnet method is still recommended as the standard-of-care protective ventilation strategy for ARDS patients (Fan et al, 2017(Fan et al, , 2018Papazian et al, 2019).…”