Recruitability and effect of PEEP in SARS-Cov-2-associated acute respiratory distress syndrome

Abstract

Background: A large proportion of patients with a SARS-Cov-2-associated respiratory failure develop an acute respiratory distress syndrome (ARDS). It has been recently suggested that SARS-Cov-2-associated ARDS may differ from usual non-SARS-Cov-2-associated ARDS by higher respiratory system compliance (C RS ), lower potential for recruitment with positive end-expiratory pressure (PEEP) contrasting with severe shunt fraction. The purpose of the study was to systematically assess respiratory mechanics and recruitability in SARS-Cov-2-associated ARDS. Methods:Gas exchanges, C RS and hemodynamics were assessed at 2 levels of PEEP (15 cmH 2 O and 5 cmH 2 O) within 36 h (day1) and from 4 to 6 days (day 5) after intubation. The recruited volume was computed as the difference between the volume expired from PEEP 15 to 5 cmH 2 O and the volume predicted by compliance at PEEP 5 cmH 2 O (or above airway opening pressure). The recruitment-to-inflation (R/I) ratio (i.e. the ratio between the recruited lung compliance and C RS at PEEP 5 cmH 2 O) was used to assess lung recruitability. A R/I ratio value higher than or equal to 0.5 was used to define highly recruitable patients. Results:The R/I ratio was calculated in 25 of the 26 enrolled patients at day 1 and in 15 patients at day 5. At day 1, 16 (64%) were considered as highly recruitable (R/I ratio median [interquartile range] 0.7 [0.55-0.94]) and 9 (36%) were considered as poorly recruitable (R/I ratio 0.41 [0.31-0.48]). The PaO 2 /FiO 2 ratio at PEEP 15 cmH 2 O was higher compared to PEEP 5 cmH 2 O only in highly recruitable patients (173 [139-236] vs 135 [89-167] mmHg; p < 0.01). Neither PaO 2 /FiO 2 or C RS measured at PEEP 15 cmH 2 O or at PEEP 5 cmH 2 O nor changes in PaO 2 /FiO 2 or C RS in response to PEEP changes allowed to identify highly or poorly recruitable patients. Conclusion:In this series of 25 patients with SARS-Cov-2 associated ARDS, 64% were considered as highly recruitable and only 36% as poorly recruitable based on the R/I ratio performed on the day of intubation. This observation suggests that a systematic R/I ratio assessment may help to guide initial PEEP titration to limit harmful effect of unnecessary high PEEP in the context of Covid-19 crisis.

COVID-19– versus non–COVID-19–related Acute Respiratory Distress Syndrome: Differences and Similarities

“…This consolidation might be explained by the long median (IQR) time interval between the onset of symptoms and orotracheal intubation (10 [7–15] d) in our study population. Other studies have reported similar findings, but we cannot rule out the possible occurrence of “patient self-inflicted lung injury” due to excessive breathing efforts and delayed intubation ( 4 , 7 ).…”

In Silico Modeling of Coronavirus Disease 2019 Acute Respiratory Distress Syndrome: Pathophysiologic Insights and Potential Management Implications

“…Several studies have examined lung recruitability in small cohorts of CARDS patients using PEEP titration ( 23 – 25 ). Results reveal a wide variation in the level of recruitability, consistent with our results.…”

“…Results reveal a wide variation in the level of recruitability, consistent with our results. Data from these studies suggest that there is potential for PEEP-induced VILI in nonrecruitable CARDS lungs (higher driving pressures due to increased PEEP in [ 24 ] and reduced compliance in [ 25 ]), and this is confirmed by the marked elevation in multiple VILI indicators in our type 1 CARDS model as PEEP is increased from 5 to 15 cm H 2 O. Based on these results, and as recently argued in ( 26 ), the use of high PEEP in type 1 CARDS patients does not appear to yield a favorable risk/benefit profile; it is, therefore, essential to evaluate the recruitability of each patient carefully before employing a standard ARDSnet low V t /high PEEP strategy.…”

Behandlungsempfehlungen zur Beatmung von COVID‑19-Patienten

“…So haben bereits Arbeiten der letzten Jahre gezeigt, dass bei ARDS-Patienten eine Individualisierung der Beatmung über eine Phänotypisierung des klinisch sehr heterogenen ARDS-Kollektivs, mortalitätsrelevante Vorteile ergeben kann [23,24]. Auch scheint die Einteilung der beatmeten COVID-19-Patienten in einen L-und H-Typ meist nicht zu gelingen [25][26][27][28][29][30]. Die Individualisierung der Beatmung kann im Wesentlichen über eine Anpassung von TV und PEEP erfolgen (.…”

“…Ein RIR <0,5 wird als geringes und ein RIR >0,5 als hohes RP interpretiert [41]. Das RIR wurde inzwischen auch an COVID-19-Patienten erprobt [27,29,32,42]. In diesen Arbeiten zeigt sich, dass das RP interindividuell sehr unterschiedlich ist.…”