Review of ‘Recruitability and effect of PEEP in COVID-19 associated Acute Respiratory Distress Syndrome’
More studies continue to shed light on how COVID-19 affects lung mechanics. Phenotype L had been suggested to dominate early on during the disease process and characterised by high compliance and low recruitability. (1,2) Consequently, high PEEP and recruitment are not indicated. (1)
A group of French investigators studied lung recruitability in 26 COVID-19 intubated ARDS patients. (3) They were significantly hypoxic (median PaO2/FiO2 ratio 135 mmHg; and most less than 200 mmHg) and none of them received NIV or HFNC before intubation.
Recruitability and the airway opening pressure (AOP) have been tested as previously described by Chen et al. (4,5). They tested the patients on two levels of PEEP 15 and 5 cmH2O, then calculated the ratio between the compliance of the recruited lung and the compliance of the baby lung (recruitment to inflation (R/I) ratio). An R/I ratio >0.5 was considered to indicate high recruitability.
The results showed 64% of patients to have high recruitability at day 1(n=16/25) and 7 out of 10 among them retained it at Day 5.
Among the poor recruitability group at Day 1 (n=9), 4 out of 5 became responsive to recruitment at Day 5. The median recruited lung volume was 277 and 338 ml in the two groups.
The high recruitability group only had better oxygenation at a PEEP of 15 compared to 5 cmH2O.
24% of patients had AOP more than 5 mmHg (median: 8).
The respiratory system compliance (CRS) was around 45 mL/cmH2O and was not statistically different between the two groups. In a recent small number cohort study, Ziehr et al reported a median compliance of 35 mL/cm H2O on day 1 in 19 intubated patients with no previous NIV or HFNC. (6)
The shunt fraction was lower in high PEEP versus lower PEEP in both recruitable and non-recruitable lungs.
The authors were able to demonstrate that neither oxygenation (PaO2/FiO2) nor CRS at low or high PEEP were able to predict recruitability. This partially contrasts the CT based findings of Gattinoni et al findings in 2006, which showed that higher potentially recruitable lungs were associated with lower PaO2/FiO2 ratio, CRS and higher shunt fraction compared to the poorly recruitable lungs. (7)
The study findings are interesting. The authors used a previously described bedside test of recruitability which may be of interest for clinicians. The measured CRS was largely preserved despite significant hypoxia, which is compatible with the two previously described phenotypes. However, as many as two thirds of those patients showed significant response to recruitment which contrast the recommendations. (1) Also, there was no haemodynamic effect of recruitment in both groups.
The preserved CRS may be secondary to the avoidance of NIV and HFNC and subsequent protection from patient self-inflicted lung injury (P-SILI). To note that the group with low recruitability had a statistically non-significant delay between symptoms onset and ICU admission; also a short delay in matter of hours between admission and intubation (median 9 hours).
All the findings and interpretations are limited by the small number of the studied patients. However, and apart from characterising the COVID-19 lungs, I think the most interesting message is the superior role of a dynamic bedside test to detect R/I over static parameters (e.g. Oxygenation, CRS). Such tests may have a role before exposing the patients to the risks of recruitment manoeuvers, high PEEP and even proning. They may have a role in the future management of various mechanically ventilated patients (4,5).
If this is to be confirmed in larger studies, it can follow the path of the established concepts in haemodynamics: superiority of dynamic parameters over static one, and test before you do.
STUDY STRENGTHS & LIMITATIONS
1. Interesting methodology (testing bedside recruitability).
2. Can impact clinical practice.
3. Interesting findings in a highly-interesting subject (Mechanical Ventilation in COVID-19).
1. Small sample size (n=26) as expected in a mono-centric trial and most recently published COVID-19 studies.
2. 20% had COPD (or asthma) which can affect lung mechanics baseline compliance.
3. Pulmonary embolism is common and can contribute to hypoxaemia, but has not been excluded.
TAKE HOME MESSAGE
A bedside lung recruitability test is feasible to calculate the R/I ratio in COVID-19 patients. Oxygenation (PaO2/FiO2 ratio) and compliance were not a good predictor of recruitability. The R/I ratio showed significant lung recruitability in a small sample of COVID-19 patients and can guide a more personalised approach to the patients.
This article review was prepared and submitted by Dr Ashraf Roshdy, Whipps Cross University Hospital – Barts Health NHS Trust, London, United Kingdom, on behalf of the ESICM Journal Review Club.
1. Gattinoni L, Chiumello D, Caironi P, et al. COVID-19 pneumonia: different respiratory treatments for different phenotypes? [published online ahead of print, 2020 Apr 14]. Intensive Care Med. 2020;1‐4. doi:10.1007/s00134-020-06033-2
2. Amit Jain & D. John Doyle. Stages or phenotypes? A critical look at COVID-19 pathophysiology. Intensive Care Medicine (2020)
3. Beloncle, F.M., Pavlovsky, B., Desprez, C. et al. Recruitability and effect of PEEP in SARS-Cov-2-associated acute respiratory distress syndrome. Ann. Intensive Care 10, 55 (2020). https://doi.org/10.1186/s13613-020-00675-7
4. Chen L, Del Sorbo L, Grieco DL, Junhasavasdikul D, Rittayamai N, Soliman I, 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;201:178–87.
5. Chen L, Del Sorbo L, Grieco DL, Shklar O, Junhasavasdikul D, Telias I, et al. Airway closure in acute respiratory distress syndrome: an underestimated and misinterpreted phenomenon. Am J Respir Crit Care Med.2018;197:132–6.
6. Gattinoni L, Caironi P, Cressoni M, Chiumello D, Ranieri VM, Quintel M, Russo S, Patroniti N, Cornejo R, Bugedo G. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med. 2006 Apr 27;354(17):1775-86.
7. Ziehr DR, Alladina J, Petri CR, Maley JH, Moskowitz A, Medoff BD, Hibbert KA, Thompson BT, Hardin CC. Respiratory Pathophysiology of Mechanically Ventilated Patients with COVID-19: A Cohort Study. Am J Respir Crit Care Med. 2020 Apr 29. doi: 10.1164/rccm.202004-1163LE.