Is COVID-19 different from other causes of acute respiratory distress syndrome?

Coronavirus disease 2019 (COVID-19) pneumonia can lead to acute hypoxemic respiratory failure. When mechanical ventilation is needed, almost all patients with COVID-19 pneumonia meet the criteria for acute respiratory distress syndrome (ARDS). The question of the specificities of COVID-19-associated ARDS compared to other causes of ARDS is of utmost importance, as it may justify changes in ventilatory strategies. This review aims to describe the pathophysiology of COVID-19-associated ARDS and discusses whether specific ventilatory strategies are required in these patients.

Intravenous immunoglobulins in patients with COVID-19-associated moderate-to-severe acute respiratory distress syndrome (ICAR): multicentre, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: Acute respiratory distress syndrome (ARDS) is a major complication of COVID-19 and is associated with high mortality and morbidity. We aimed to assess whether intravenous immunoglobulins (IVIG) could improve outcomes by reducing inflammation-mediated lung injury. METHODS: In this multicentre, double-blind, placebo-controlled trial, done at 43 centres in France, we randomly assigned patients (1:1) receiving invasive mechanical ventilation for up to 72 h with PCR confirmed COVID-19 and associated moderate-to-severe ARDS to receive either IVIG (2 g/kg over 4 days) or placebo. Random assignment was done with a web-based system and was stratified according to the participating centre and the duration of invasive mechanical ventilation before inclusion in the trial (<12 h, 12-24 h, and >24-72 h), and treatment was administered within the first 96 h of invasive mechanical ventilation. To minimise the risk of adverse events, the IVIG administration was divided into four perfusions of 0·5 g/kg each administered over at least 8 hours. Patients in the placebo group received an equivalent volume of sodium chloride 0·9% (10 mL/kg) over the same period. The primary outcome was the number of ventilation-free days by day 28, assessed according to the intention-to-treat principle. This trial was registered on ClinicalTrials.gov, NCT04350580. FINDINGS: Between April 3, and October 20, 2020, 146 patients (43 [29%] women) were eligible for inclusion and randomly assigned: 69 (47%) patients to the IVIG group and 77 (53%) to the placebo group. The intention-to-treat analysis showed no statistical difference in the median number of ventilation-free days at day 28 between the IVIG group (0·0 [IQR 0·0-8·0]) and the placebo group (0·0 [0·0-6·0]; difference estimate 0·0 [0·0-0·0]; p=0·21). Serious adverse events were more frequent in the IVIG group (78 events in 22 [32%] patients) than in the placebo group (47 events in 15 [20%] patients; p=0·089). INTERPRETATION: In patients with COVID-19 who received invasive mechanical ventilation for moderate-to-severe ARDS, IVIG did not improve clinical outcomes at day 28 and tended to be associated with an increased frequency of serious adverse events, although not significant. The effect of IVIGs on earlier disease stages of COVID-19 should be assessed in future trials. FUNDING: Programme Hospitalier de Recherche Clinique.

Longitudinal changes in compliance, oxygenation and ventilatory ratio in COVID-19 versus non-COVID-19 pulmonary acute respiratory distress syndrome.

BACKGROUND: Differences in physiology of ARDS have been described between COVID-19 and non-COVID-19 patients. This study aimed to compare initial values and longitudinal changes in respiratory system compliance (CRS), oxygenation parameters and ventilatory ratio (VR) in patients with COVID-19 and non-COVID-19 pulmonary ARDS matched on oxygenation. METHODS: 135 patients with COVID-19 ARDS from two centers were included in a physiological study; 767 non-COVID-19 ARDS from a clinical trial were used for the purpose of at least 1:2 matching. A propensity-matching was based on age, severity score, oxygenation, positive end-expiratory pressure (PEEP) and pulmonary cause of ARDS and allowed to include 112 COVID-19 and 198 non-COVID pulmonary ARDS. RESULTS: The two groups were similar on initial oxygenation. COVID-19 patients had a higher body mass index, higher CRS at day 1 (median [IQR], 35 [28-44] vs 32 [26-38] ml cmH2O-1, p = 0.037). At day 1, CRS was correlated with oxygenation only in non-COVID-19 patients; 61.6% and 68.2% of COVID-19 and non-COVID-19 pulmonary ARDS were still ventilated at day 7 (p = 0.241). Oxygenation became lower in COVID-19 than in non-COVID-19 patients at days 3 and 7, while CRS became similar. VR was lower at day 1 in COVID-19 than in non-COVID-19 patients but increased from day 1 to 7 only in COVID-19 patients. VR was higher at days 1, 3 and 7 in the COVID-19 patients ventilated using heat and moisture exchangers compared to heated humidifiers. After adjustment on PaO2/FiO2, PEEP and humidification device, CRS and VR were found not different between COVID-19 and non-COVID-19 patients at day 7. Day-28 mortality did not differ between COVID-19 and non-COVID-19 patients (25.9% and 23.7%, respectively, p = 0.666). CONCLUSIONS: For a similar initial oxygenation, COVID-19 ARDS initially differs from classical ARDS by a higher CRS, dissociated from oxygenation. CRS become similar for patients remaining on mechanical ventilation during the first week of evolution, but oxygenation becomes lower in COVID-19 patients. TRIAL REGISTRATION: clinicaltrials.gov NCT04385004.

Continuous positive airway pressure for respiratory support during COVID-19 pandemic: a frugal approach from bench to bedside.

BACKGROUND: We describe a frugal approach (focusing on needs, performance, and costs) to manage a massive influx of COVID-19 patients with acute hypoxemic respiratory failure (AHRF) using the Boussignac valve protected by a filter ("Filter Frugal CPAP", FF-CPAP) in and out the ICU. METHODS: (1) A bench study measured the impact of two filters with different mechanical properties on CPAP performances, and pressures were also measured in patients. (2) Non-ICU healthcare staff working in COVID-19 intermediate care units were trained with a video tutorial posted on a massive open online course. (3) A clinical study assessed the feasibility and safety of using FF-CPAP to maintain oxygenation and manage patients out of the ICU during a massive outbreak. RESULTS: Bench assessments showed that adding a filter did not affect the effective pressure delivered to the patient. The resistive load induced by the filter variably increased the simulated patient's work of breathing (6-34%) needed to sustain the tidal volume, depending on the filter's resistance, respiratory mechanics and basal inspiratory effort. In patients, FF-CPAP achieved pressures similar to those obtained on the bench. The massive training tool provided precious information on the use of Boussignac FF-CPAP on COVID-19 patients. Then 85 COVID-19 patients with ICU admission criteria over a 1-month period were studied upon FF-CPAP initiation for AHRF. FF-CPAP significantly decreased respiratory rate and increased SpO2. Thirty-six (43%) patients presented with respiratory indications for intubation prior to FF-CPAP initiation, and 13 (36%) of them improved without intubation. Overall, 31 patients (36%) improved with FF-CPAP alone and 17 patients (20%) did not require ICU admission. Patients with a respiratory rate > 32 breaths/min upon FF-CPAP initiation had a higher cumulative probability of intubation (p < 0.001 by log-rank test). CONCLUSION: Adding a filter to the Boussignac valve does not affect the delivered pressure but may variably increase the resistive load depending on the filter used. Clinical assessment suggests that FF-CPAP is a frugal solution to provide a ventilatory support and improve oxygenation to numerous patients suffering from AHRF in the context of a massive outbreak.

Reliability and limits of transport-ventilators to safely ventilate severe patients in special surge situations.

BACKGROUND: Intensive Care Units (ICU) have sometimes been overwhelmed by the surge of COVID-19 patients. Extending ICU capacity can be limited by the lack of air and oxygen pressure sources available. Transport ventilators requiring only one O2 source may be used in such places. OBJECTIVE: To evaluate the performances of four transport ventilators and an ICU ventilator in simulated severe respiratory conditions. MATERIALS AND METHODS: Two pneumatic transport ventilators, (Oxylog 3000, Draeger; Osiris 3, Air Liquide Medical Systems), two turbine transport ventilators (Elisee 350, ResMed; Monnal T60, Air Liquide Medical Systems) and an ICU ventilator (Engström Carestation-GE Healthcare) were evaluated on a Michigan test lung. We tested each ventilator with different set volumes (Vtset = 350, 450, 550 ml) and compliances (20 or 50 ml/cmH2O) and a resistance of 15 cmH2O/l/s based on values described in COVID-19 Acute Respiratory Distress Syndrome. Volume error (percentage of Vtset) with P0.1 of 4 cmH2O and trigger delay during assist-control ventilation simulating spontaneous breathing activity with P0.1 of 4 cmH2O and 8 cmH2O were measured. RESULTS: Grouping all conditions, the volume error was 2.9 ± 2.2% for Engström Carestation; 3.6 ± 3.9% for Osiris 3; 2.5 ± 2.1% for Oxylog 3000; 5.4 ± 2.7% for Monnal T60 and 8.8 ± 4.8% for Elisee 350. Grouping all conditions (P0.1 of 4 cmH2O and 8 cmH2O), trigger delay was 50 ± 11 ms, 71 ± 8 ms, 132 ± 22 ms, 60 ± 12 and 67 ± 6 ms for Engström Carestation, Osiris 3, Oxylog 3000, Monnal T60 and Elisee 350, respectively. CONCLUSIONS: In surge situations such as COVID-19 pandemic, transport ventilators may be used to accurately control delivered volumes in locations, where only oxygen pressure supply is available. Performances regarding triggering function are acceptable for three out of the four transport ventilators tested.

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

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 (CRS), 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, CRS and hemodynamics were assessed at 2 levels of PEEP (15 cmH2O and 5 cmH2O) 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 cmH2O and the volume predicted by compliance at PEEP 5 cmH2O (or above airway opening pressure). The recruitment-to-inflation (R/I) ratio (i.e. the ratio between the recruited lung compliance and CRS at PEEP 5 cmH2O) 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 PaO2/FiO2 ratio at PEEP 15 cmH2O was higher compared to PEEP 5 cmH2O only in highly recruitable patients (173 [139-236] vs 135 [89-167] mmHg; p < 0.01). Neither PaO2/FiO2 or CRS measured at PEEP 15 cmH2O or at PEEP 5 cmH2O nor changes in PaO2/FiO2 or CRS 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.