Lung Recruitability in COVID-19-associated Acute Respiratory Distress Syndrome: A Single-Center Observational Study.

TLDR: A new mechanics-based index is described to directly quantify the potential for lung recruitment, called the recruitment-to-inflation ratio (R/I ratio), which estimates how much of an increase in endexpiratory lung volume induced by PEEP is distributed between the recruited lung (recruitment) and the inflation and/or hyperinflation of the “baby lung” when a higher PEP is applied.

Abstract: The coronavirus disease (COVID-19) outbreak was declared a public health emergency by the World Health Organization on January 30, 2020. A majority (67–85%) of critically ill patients who were admitted to an ICU with a confirmed infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) developed acute respiratory distress syndrome (ARDS) (1, 2). An observational study of 52 cases at a single center, the Jinyintan Hospital (a temporary designated center for critically ill patients with COVID-19) in Wuhan, China, showed that these patients had a high mortality (61.5%) (2). For patients with ARDS, the specific characteristics of this syndrome, such as the respiratory mechanics, remain unknown. In particular, an important clinical question with regard to personalizing the management of these patients is whether the lungs are recruitable with high positive end-expiratory pressure (PEEP) for each individual patient. Two of the authors of this study (C.P. andH.Q.) were directly in charge of these critically ill patients with SARS-CoV-2–associated ARDS at the Jinyintan Hospital. Clinical decisions about the right PEEP level were challenging, especially when the PEEP was adapted based on the NIH-NHLBI ARDS Network PEEP-FIO2 table. With high PEEP (e.g., 15 cm H2O), the plateau pressure often became extremely high (.45 cm H2O) and patients seemed poorly responsive, often displaying only modest improvement in oxygenation, with increased driving pressure and/or development of hypotension. Because of the high clinical workload and the very constrained environment, these bedside observations were not done in a systematic manner or recorded. Until recently, quantitative assessments of a patient’s potential for lung recruitment at the bedside were very imprecise (3). Recently, members of our group (including L.C., M.C.S., and L.B.) described a new mechanics-based index to directly quantify the potential for lung recruitment, called the recruitment-to-inflation ratio (R/I ratio) (4). It estimates how much of an increase in endexpiratory lung volume induced by PEEP is distributed between the recruited lung (recruitment) and the inflation and/or hyperinflation of the “baby lung” when a higher PEEP is applied. It ranges from 0 to 2.0, and the higher the R/I ratio, the higher the potential for lung recruitment. An R/I ratio of 1.0 suggests a high likelihood of recruitment, as the volume will be distributed similarly to the recruited lung and the baby lung. This method can be performed at the bedside and requires only a single-breath maneuver on any ventilator. This maneuver is particularly useful in conditions of high risk of virus transmission by disconnection, transport, or complex procedures. The clinicians in Wuhan decided to use this measure of recruitment in a systematic way in a series of patients with SARS-CoV-2–associated ARDS, and also to assess the effect of body positioning.