key: cord-0707390-s3uffq0c
authors: Stevic, Neven; Chatelain, Emeric; Dargent, Auguste; Argaud, Laurent; Cour, Martin; Guérin, Claude
title: Lung Recruitability Evaluated by Recruitment-to-Inflation Ratio and Lung Ultrasound in COVID-19 Acute Respiratory Distress Syndrome
date: 2021-04-15
journal: Am J Respir Crit Care Med
DOI: 10.1164/rccm.202012-4447le
sha: 76371781fc4b972379c7a65a8fcb14baad90857f
doc_id: 707390
cord_uid: s3uffq0c

nan

A substantial proportion of patients with coronavirus disease admitted to the ICU require invasive mechanical ventilation for acute respiratory distress syndrome (ARDS), which is still associated with a high mortality rate (1) . Applying the optimal positive end-expiratory pressure (PEEP) to ensure lung recruitment while limiting lung hyperinflation remains challenging in ARDS (2, 3) . Yet, there are a few simple tools that might help personalize the level of PEEP in those patients at the bedside. Among them, the lung ultrasound (LUS) aeration score and the recruitment-toinflation (R/I) ratio have the potential to identify patients who are more likely to benefit from PEEP (2) . Previous studies indeed suggested that LUS could assess spatial distribution of PEEPinduced lung recruitment but does not reliably detect hyperinflation (4, 5) . The R/I ratio is a tool that has recently been developed to evaluate both the potential for lung recruitment and the risk for hyperinflation, but it does not provide regional information about lung recruitment (6) (7) (8) . Therefore, these two tools, readily available at the bedside in most ICUs, could provide additive and complementary information on lung recruitment.

In the present study, we aimed to assess lung recruitability simultaneously by the R/I ratio and the LUS in patients with COVID-19-related ARDS.

We conducted a prospective observational study between March 31 and October 29, 2020, in a 26-bed university-affiliated ICU in Lyon, France, which was approved by our institutional ethics committee.

Consecutive adult patients with COVID-19-associated ARDS in whom PEEP-induced lung recruitment was assessed simultaneously with both the LUS and the R/I ratio within the first 48 hours after intubation were included. COVID-19 was biologically confirmed and ARDS diagnosis was based on the Berlin criteria.

Ventilator settings and respiratory mechanics were recorded in sedated and curarized patients, ventilated in volume control with an Evita XL respirator (Dräger Medical). All measurements were performed in patients in the semirecumbent position. The presence of complete airway closure was assessed by measuring the airway opening pressure (AOP), as previously described (6) .

PEEP-induced lung recruitment was assessed by the R/I ratio with high and low PEEP set at 15 cm H 2 O (for 30 min) and 5 cm H 2 O, respectively; in the event that AOP was .5 cm H 2 O, R/I was calculated with AOP instead of 5 cm H 2 O (6-8). Briefly, the recruited volume from low to high PEEP divided by the effective pressure change gave the compliance of the recruited lung; the ratio of this compliance to the compliance at low PEEP gave the R/I ratio (6) (7) (8) . In the absence of a universally validated cut-off value, the median R/I ratio of the cohort was used to classify patients as high and low recruiters.

LUS scores were calculated at PEEP 15 cm H 2 O and PEEP 5 cm H 2 O, by summing regional scores (0-3 points) obtained in six regions of each lung (i.e., up and down anterior, medial, and posterior chest wall) (4, 5, 9, 10) . The delta LUS (DLUS) score was defined as the difference obtained between low and high PEEP. The LUS reaeration score was also determined according to the method validated by Bouhemad and colleagues (5) . All operators were experimented (.100 LUS procedures) and blinded to the R/I ratio results.

Continuous data are expressed as median (first to third quartile). Comparisons were done using nonparametrical tests. Correlations were assessed with the rho Spearman's correlation test and its 95% confidence intervals (CIs).

Twenty-four patients (age: 69 [63-73] yr; sex ratio: 5) were included ( Table 1 ). The time from first symptoms to ICU admission was 8 (7-10) days. Twenty-two patients (88%) were treated with highflow nasal oxygen therapy or noninvasive ventilation before intubation.

Most patients (n = 22/24, 92%) presented moderate to severe ARDS (Table 1) . Complete airway closure was present in one-third of cases; none of them had an AOP above the high PEEP ( Table 1 ). The median R/I ratio was 0.7, thus defining 12 high recruiters (0.8 [0.8-1.1]) and 12 low recruiters (0.5 [0.3-0.6]) ( Table 1 ). The LUS scores measured at low and high PEEP did not significantly differ between the two subgroups, whereas both DLUS and LUS reaeration scores were significantly higher in high recruiters ( Table 1) . The difference in LUS reaeration scores was mainly driven by more reaeration in lateral and posterior lung regions in the recruiters ( (Figure 1 ).

The main and new finding of the present study is that the R/I ratio at a threshold of 0.7 correlated with the LUS reaeration score, in particular in patients without complete airway closure. To the best of our knowledge, this is the first report combining the R/I ratio and LUS to assess lung recruitment, even considering patients with non-COVID-19 ARDS.

Our result extends the previous validation of the LUS reaeration score against the recruited volume measured by the volume-pressure curve (4), by consistently underscoring the need to consider AOP when assessing lung recruitment by the spirometric methods. In our study, the LUS reaeration score was significantly higher in the posterior lung regions of recruiters than in nonrecruiters but not in the anterior lung regions. This important finding suggests that lung recruitment occurred in the dependent lung regions, which is the desirable effect of PEEP or of any other method used to elicit this process. The fact that compliance of the respiratory system was greater in the former than in the latter, and that ventilatory ratio, a marker of dead space, was not different between the two groups, argue against a significant hyperinflation.

In the princeps study by Chen and colleagues in non-COVID-19 ARDS, the R/I ratio that differentiated recruiters from nonrecruiters, corresponding to the median value of their cohort, was 0.5. In the present study, the median value of the R/I ratio was 0.7, which was used for the analysis. Nevertheless, we found similar results at a threshold of 0.5 (data not shown).

Our study is limited by the fact that it is single-centered and that the gold standard method for lung recruitment assessment (i.e., quantitative computed tomography scan) was not used. Also, 1 (0 to 2) 2 (0 to 2) 1 (0 to 2) 0.633 Lateral lung regions 0 (0 to 1) 1 (0 to 2) 0 (0 to 1) 0.077 Posterior lung regions 1 (0 to 1) 1 (1 to 2) 0 (0 to 1) 0.009 LUS reaeration score 3 (1 to 5) 4 (3 to 6) 2 (0 to 3) 0.017 Anterior lung regions 1 (0 to 2) 2 (0 to 3) 1 (0 to 2) 0.593 Lateral lung regions 0 (0 to 1) 1 (0 to 3) 0 (0 to 1) 0.084 Posterior lung regions 1 (0 to 1) 1 (1 to 2) 0 (0 to 1) 0.009

Definitions of abbreviations: AOP = airway opening pressure; ARDS = acute respiratory distress syndrome; COPD = chronic obstructive pulmonary disease; Crec = compliance of the recruited lung; Crs = compliance of the respiratory system; LUS = lung ultrasound score; PBW = predicted body weight; PEEP = positive end-expiratory pressure; Pplat= plateau pressure; R/I ratio = recruitment-to-inflation ratio; SAPS II = Simplified Acute Physiology Score II; Sp O 2 = oxygen saturation as measured by pulse oximetry; Vrec = recruited lung volume. Data are expressed as median (first to third quartile) unless otherwise indicated. *P values refer to the comparison between the high-and low-recruiter groups. † Defined as (VĖ 3 Pa CO 2 )/(predicted body weight 3 100 3 37.5 Pseudomonas aeruginosa in the Cystic Fibrosis Airway: Does It Deserve Its Reputation as a Predatory "Bully"?

To the Editor:

Despite similarities in global standards of care in cystic fibrosis (CF), one long-standing area of regional disagreement is prevention of 

Clinical characteristics and day-90 outcomes of 4244 critically ill adults with COVID-19: a prospective cohort study

Positive endexpiratory pressure-induced recruited lung volume measured by volume-pressure curves in acute respiratory distress syndrome: a physiologic systematic review and meta-analysis

High versus low PEEP in non-recruitable collapsed lung tissue: possible implications for patients with COVID-19

Bedside ultrasound assessment of positive end-expiratory pressure-induced lung recruitment

Assessment of lung aeration and recruitment by CT scan and ultrasound in acute respiratory distress syndrome patients

Potential for lung recruitment estimated by the recruitment-to-inflation ratio in acute respiratory distress syndrome: a clinical trial

Lung recruitability in COVID-19-associated acute respiratory distress syndrome: a single-center observational study

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

ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin definition

AZUREA Network. Comparative study of lung ultrasound and chest computed tomography scan in the assessment of severity of confirmed COVID-19 pneumonia