Physiological Effects of the Open Lung Approach in Patients with Early, Mild, Diffuse Acute Respiratory Distress Syndrome

Abstract

The OLA decreases the driving pressure and improves the oxygenation and lung mechanics in patients with early, mild, diffuse ARDS. EIT is useful to assess the impact of OLA on regional tidal volume distribution.

Early severe acute respiratory distress syndrome: What’s going on? Part I: pathophysiology

“…Vt and PEEP observed on day 1 were not associated with survival. Conversely, reductions in Vt or increases in PEEP driven by random treatment-group assignment were beneficial only if they were associated with decreases in the driving pressure (data in [92]; Fig. 2 in [17]).…”

“…prevention of cyclical collapse at end-expiration by positive end-expiratory pressure (loop B in rabbits: Fig. 5 in [174]) rather than to recruit alveoli by recruiting maneuvers, at end-inspiration Finally, a comparison showed differences between trial-PEEP (PEEP at which the greatest PaO 2 improvement is observed [80] [These data suggest (Table 1, part II) to: a) ascertain severe ARDS: P/F < 100 after 30 min (Vt ~7 mL kg -1 , PEEP = 10 cm H 2 O, and FiO 2 = 1) [20] or preferably PEEP = 5 cm H 2 O according to the Berlin definition [19] and Grasso [92] b) perform investigations (CT scan, fiberoptic bronchoscopy, etc.) and iterative echocardiography/circulatory optimization upfront c) move early to alveoli recruitment (minimize alveolar "penumbra") using an esophageal catheter or a trial-PEEP (keeping in mind that an SaO 2 = = 88−92% is to be considered in the setting of CMV [141,160], while an SaO 2 = 95−100% is to be considered in the setting of SV [161]]…”

“…A last factor in explaining the absence of reduced mortality in large trials may be the inclusion of patients with high intra-abdominal, pleural or esophageal pressures [10] Anatomical heterogeneity: Before applying PEEP to highly recruitable lungs, assessing recruitability with a CT scan is needed. Now, electrical impedance tomography allows one to avoid transportation of unstable patients to the CT scan [92]. In the setting of early ARDS (< 10 days) a) 27% of the patients present lower lobes with mechanical/compression atelectasis (pure loss of aeration) while 73% of the patients present inflammatory atelectasis (loss of aeration + excess of lung tissue) b) ARDS may be characterized by evenly distributed diffuse alterations (23% of the patients; mortality rate: 75%; lower inflection point: 8 ± 2 cm H 2 O) vs. lobar attenuations predominating in the lower lobes (36%; mortality: 42%; LIP: 5 ± 2 cm H 2 O) vs. patchy attenuations unevenly distributed in the 2 lungs (40%; mortality: 41%; LIP: 6 ± 3 cm H 2 O) [87,89].…”

“…In the setting of severe diffuse ARDS, early in the disease, when recruitability is expected to make important difference in mortality, early ventilator management is key [177]: high PEEP-low Vt are beneficial in severe early diffuse ARDS [8]. Accordingly, in early mild diffuse ARDS, Grasso observes that increasing PEEP lowers driving pressure [92]. A meta-analysis [169] confirms that the higher the predicted mortality, the greater the mortality reduction associated with high PEEP: the sicker the patients, the higher the PEEP should be viii) Recently, transpulmonary pressure was estimated without the use of an esophageal catheter [133].…”

“…6 in [81] and Fig. 1 in [82]), electrical impedance tomography [92], compliance or transpulmonary end-inspiratory pressure [17]. The compliance is related to the amount of aerated tissue but not the amount of non-aerated tissue.…”