Observations of a small sample of patients with acute respiratory distress syndrome (ARDS) related to COVID-19 infection suggested that lung recruitability, which is related to the restoration of aeration in lung tissue using positive end-expiratory pressure (PEEP), was affected by body position. These findings were published in the American Journal of Respiratory Critical Care Medicine.1
The goal of this study was to evaluate lung recruitability in patients with ARDS, a condition characterized by widespread inflammation of lung tissue, admitted to the intensive care unit (ICU) with a confirmed COVID-19 infection and placed on invasive mechanical ventillation.1
The percentage of recruitable lung, defined in an earlier study as “the proportion of the total lung weight accounted for by nonaerated lung tissue in which aeration was restored (confirmed by CT) by an airway pressure of 45 cm of water from an airway pressure of 5 cm of water,”is an important parameter in assessing the potential benefit of PEEP.2
In this retrospective study, bedside assessment of lung recruitability was evaluated from data that were recorded in the medical charts over a 6-day period during February 2020 for a series of 12 patients with ARDS related to COVID-19 infection who were receiving treatment with PEEP at a single hospital in China.1
In contrast to the method previously described, a single-breath maneuver was used to measure the recruitment-to-inflation (R/I) ratio which “estimates how much of an increase in end-expiratory 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.”3 In this context, the term baby lung refers to a model of the amount of normally aerated tissue in severe ARDS at the end of expiration, estimated to be that of a healthy child aged 5 or 6 years.4 Using this method, R/I ratios of 0 to 2 are possible, with an R/I ratio of 1.0 considered to be suggestive of lung recruitability.1,3,4
A key finding from this study was that there was a significant association between improved lung recruitability in those patients for whom body position was alternated between supine and prone compared with those who were not placed in a prone position (P =.020).1
Although they mentioned that this study was not randomized and included only a small number of patients who may or may not be generally representative of critically ill patients with ARDS related to COVID-19 infection, the study authors concluded that the “surprising finding that alternating body position is followed with increased lung recruitability is interesting but needs to be confirmed.”1
1. Pan C, Chen L, Lu C, et al. Lung recruitability in SARS-CoV-2 associated acute respiratory distress syndrome: a single-center, observational study [published online March 23, 2020].Am J Respir Crit Care Med. doi:10.1164/rccm.202003-0527LE
2. Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med. 2006;354(17):1775-1786.
3. Chen L, Del Sorbo L, Grieco DL, et al. Potential for lung recruitment estimated by the recruitment-to-inflation ratio in acute respiratory distress syndrome. A clinical trial. Am J Respir Crit Care Med 2020;201(2):178-187.
4. Gattinoni L, Pesenti A. The concept of “baby lung.” Intensive Care Med. 2005;31(6):776-784.