PEEP-induced alveolar recruitment in patients with COVID-19 pneumonia: take the right time!

To the Editor,

Acute respiratory disease syndrome (ARDS) related to novel coronavirus-19 disease (COVID-19) is a specific pathological condition characterized, at an early stage, by normal or high respiratory system compliance and hypoxemia [1]. This so-called “low” phenotype of ARDS associated to COVID-19 is also characterized by a low lung weight, with ground-glass opacities located in subpleural areas at chest computed tomography scan (CT-scan), and low response to lung recruitment [1]. In case of adverse evolution of COVID-19 pneumonia and high stress ventilation as for patient-self-inflicted lung-injury induced by vigorous negative pressure developed during spontaneous breathing or non-invasively assisted breath, “low” phenotype may worsen in “high” phenotype with low respiratory system compliance, high right-to-left shunt, high lung weight, and good response to lung recruitment. Thus, while assuring a protective ventilation, a high positive end-expiratory pressure (PEEP) strategy, similar to that employed in managing severe COVID-19-free ARDS, can be pursued when a predominant “high” phenotype is observed [1].

In the interesting investigation by Ball and colleagues [2], the authors addressed the effects of PEEP on alveolar recruitment evaluated through CT-scan. They concluded against the adoption of high PEEP strategy because it did not lead to a substantial alveolar recruitment and worsened respiratory mechanics. However, while reading in details the investigation by Ball et all [2], some concerns raise about the modalities of PEEP application proposed. First of all, no lung recruitment maneuver was performed prior to switch from 8 to 16 cmH₂O of PEEP. This might have led to the occurrence of lung overdistention and partial atelectasis resolution, limiting the potential positive effects exerted by PEEP in those circumstances. Indeed, in ARDS patients, lung recruitment maneuver is usually performed to normalize lung volumes both during invasive [3] and non-invasive mechanical ventilation [4]. Lastly, the assessment of lung recruitment through CT-scan was performed 1 min following the application of 16 cmH₂O-PEEP. This time frame might not be enough to induce an improvement in the extent of aerated lung tissue and reduction of poorly/non aerated lung zones. According to Chiumello et al. [5], the evaluation of lung aeration at 5 and 15 cmH₂O of PEEP through CT-scan and lung ultrasound was performed during a 2-h-lasting trial. Also, the changes in respiratory system compliance induced by a PEEP of 15 cmH₂O were clinically relevant at 5 and 15 min from the baseline assessment with a 5 cmH₂O of PEEP in intubated ARDS patients [3].

Abbreviations

ARDS

Acute respiratory disease syndrome

COVID-19

Novel coronavirus-19 disease

PEEP

Positive end-expiratory pressure

CT-scan

Computed tomography scan

Authors contributions

All authors listed concur with the submitted version of the manuscript and with the listing of the authors. In particular, all authors meet the following criteria for authorship: substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; drafting or revising the manuscript; final approval of the version submitted for publication; accountability for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. GC, EDR: conception of the work; GC, RS: manuscript drafting; GC, EDR: final version revision. All author read and approved the final manuscript.

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