key: cord-0737965-gnwi1t0c
authors: Abou-Arab, Osama; Haye, Guillaume; Beyls, Christophe; Huette, Pierre; Roger, Pierre-Alexandre; Guilbart, Mathieu; Bernasinski, Michaël; Besserve, Patricia; Trojette, Faouzi; Dupont, Hervé; Jounieaux, Vincent; Mahjoub, Yazine
title: Hypoxemia and prone position in mechanically ventilated Covid-19 patients: a prospective cohort study
date: 2020-11-04
journal: Can J Anaesth
DOI: 10.1007/s12630-020-01844-9
sha: 7fb7303964041228869ae576bc4be20bf727a9b5
doc_id: 737965
cord_uid: gnwi1t0c

nan

During the COVID-19 outbreak, severe cases of COVID-19 related acute respiratory distress syndrome (ARDS) were admitted to our tertiary hospital ICU. The benefits of prone position (PP) on survival have been highlighted in previous ARDS studies. 1 The aim of the study was to report the effects of PP in mechanically ventilated patients with COVID-19 related ARDS.

Between March 1st and April 30th, we prospectively included all patients admitted to our ICU with COVID-19 related acute respiratory failure. COVID-19 was diagnosed by Rt-PCR on a nasopharyngeal swab. During this period, 70 patients with COVID-19 diagnosis were admitted; 64 (91%) received invasive mechanical ventilation during the course of the disease. They were ventilated with low tidal volume (B 6ml.kg -1 ), plateau pressure below 30 cmH 2 O, low driving pressure (B15 cmH 2 O) and PEEP according to the strategy proposed by the ARDS Network. 2 Patients for whom PaO 2 /FiO 2 ratio remained below 150 for 12 hours despite this protective ventilation, received at least one 16hour PP session (flow chart in Electronic supplementary material (ESM)). All patients were sedated and paralyzed before PP. Respiratory parameters were recorded before and at the end of the first 16-hour PP session. The compliance of the respiratory system (Crs) was calculated as tidal volume/(plateau pressure minus end-expiratory pressure). Ventilator setting were not modified during PP; and FiO 2 was adapted for a target SpO 2 of 92%.

Local IRB waived the need for written consent and data collection was approved by the French licensing authority (number: PI2020_843_0026). Oral and written information was provided to the patients and their families. All parameters were compared using a Wilcoxon rank-sum test and P \ 0.05 was considered as significant.

Twenty-five patients were analyzed. Clinical data appear in ESM- PP significantly improved oxygenation without any change in PaCO 2 or Crs in our population of mainly male patients. One of the beneficial effect of PP is the recruitment of non-aerated areas of the lungs. Previous studies have shown that improvement of PaCO 2 with PP suggests lung recruitment. 3 We found that PaCO 2 , plateau pressure, Crs and ventilatory ratio (a surrogate for dead space; see ESM3) remained stable suggesting a lack of significant lung recruitment induced by PP . Hence, the increase in PaO 2 /FiO 2 ratio may be explained by an Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12630-020-01844-9) contains supplementary material, which is available to authorized users. improvement in ventilation-to-perfusion ratio (VA/Q). Because ventilation is unchanged, VA/Q increase could only be explained by a decrease in pulmonary capillary flow (Q). If the decrease of Q is sufficient to improve oxygenation, we may suggest that a major mechanism involved in COVID-19 related ARDS is a VA/Q mismatch and probably an intra pulmonary shunt. 4 Gattinoni et al. have observed an increased shunt fraction in COVID-19 ''atypical ARDS'' and suggested ''hyperperfusion'' of gasless tissue. 5 In this hypothesis, because lung shape is conical, the distribution of the shunt that predominates in the larger (posterior) part may be reduced by PP explaining the significant improve in PaO 2 /FiO 2 ratio.

Despite its limited sample size, this study suggests that PP may improve oxygenation without any changes in ventilatory parameters highlighting the possible role of a hidden intra-pulmonary shunt. Further investigations are mandatory before any formal conclusion. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Figure 1 Effect of prone positioning on respiratory parameters. Changes in PaO 2 / FiO 2 ratio, respiratory system compliance (Crs) and PaCO 2 from supine to prone position

Prone position for acute respiratory distress syndrome. A systematic review and meta-analysis

Effect of lung recruitment and titrated positive end-expiratory pressure (PEEP) vs low PEEP on mortality in patients with acute respiratory distress syndrome: a randomized clinical trial

Relationship between gas exchange response to prone position and lung recruitability during acute respiratory failure

Severe Covid-19 disease: rather AVDS* than ARDS?

COVID-19 Does Not Lead to a ''Typical'' Acute Respiratory Distress Syndrome

Acknowledgements The authors thanks Prof. Antoine Gabrion and the ''surgical DV team'' for their help during the crisis.

Funding Only institutional funds were used for this study.Implication statement In this study on severe ARDS related to Covid-19, prone positioning enhances oxygenation without improvement neither in PaCO 2 nor in respiratory compliance. This effect may be due to a decrease in intra-pulmonary shunt related to Covid-19.