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Respiratory Mechanics and Gas Exchanges in the Early Course of COVID‑19 ARDS: a Hypothesis‑Generating Study J.‑L

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Respiratory Mechanics and Gas Exchanges in the Early Course of COVID‑19 ARDS: a Hypothesis‑Generating Study J.‑L Diehl et al. Ann. Intensive Care (2020) 10:95 https://doi.org/10.1186/s13613-020-00716-1 RESEARCH Open Access Respiratory mechanics and gas exchanges in the early course of COVID-19 ARDS: a hypothesis-generating study J.‑L. Diehl1,2* , N. Peron3, R. Chocron4,5, B. Debuc6, E. Guerot3, C. Hauw‑Berlemont3, B. Hermann3, J. L. Augy3, R. Younan3, A. Novara3, J. Langlais3, L. Khider7, N. Gendron1,8, G. Goudot5, J.‑F. Fagon3, T. Mirault4,9 and D. M. Smadja1,8 Abstract Rationale: COVID‑19 ARDS could difer from typical forms of the syndrome. Objective: Pulmonary microvascular injury and thrombosis are increasingly reported as constitutive features of COVID‑19 respiratory failure. Our aim was to study pulmonary mechanics and gas exchanges in COVID‑2019 ARDS patients studied early after initiating protective invasive mechanical ventilation, seeking after corresponding patho‑ physiological and biological characteristics. Methods: Between March 22 and March 30, 2020 respiratory mechanics, gas exchanges, circulating endothelial cells (CEC) as markers of endothelial damage, and D‑dimers were studied in 22 moderate‑to‑severe COVID‑19 ARDS patients, 1 [1–4] day after intubation (median [IQR]). Measurements and main results: Thirteen moderate and 9 severe COVID‑19 ARDS patients were studied after initiation of high PEEP protective mechanical ventilation. We observed moderately decreased respiratory system compliance: 39.5 [33.1–44.7] mL/cmH2O and end‑expiratory lung volume: 2100 [1721–2434] mL. Gas exchanges were characterized by hypercapnia 55 [44–62] mmHg, high physiological dead‑space (VD/VT): 75 [69–85.5] % and ventila‑ 2 tory ratio (VR): 2.9 [2.2–3.4]. VD/VT and VR were signifcantly correlated: r 0.24, p 0.014. No pulmonary embolism was suspected at the time of measurements. CECs and D‑dimers were elevated= as= compared to normal values: 24 [12–46] cells per mL and 1483 [999–2217] ng/mL, respectively. Conclusions: We observed early in the course of COVID‑19 ARDS high VD/VT in association with biological markers of endothelial damage and thrombosis. High VD/VT can be explained by high PEEP settings and added instrumental dead space, with a possible associated role of COVID‑19‑triggered pulmonary microvascular endothelial damage and microthrombotic process. Keywords: ARDS, COVID‑19, Physiological dead‑space, Ventilatory ratio Introduction Patients with Covid-19 pneumonia fulflling Berlin crite- ria of ARDS may present some specifc features, as com- pared to typical forms of the syndrome [1]. Such reported *Correspondence: jean‑[email protected] features are severe hypoxemia contrasting with relative 2 Intensive Care Unit and Biosurgical Research Lab (Carpentier preservation in respiratory mechanics [1, 2], and a com- Foundation), AH‑HP, Georges Pompidou European Hospital, 20 Rue mon hypercapnia with high ventilatory ratio (VR) [2]. Leblanc, 75015 Paris, France Full list of author information is available at the end of the article Low recruitability, improved by body positioning, has © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://crea‑ tivecommons.org/licenses/by/4.0/. Diehl et al. Ann. Intensive Care (2020) 10:95 Page 2 of 7 been reported by some authors [3], while others men- PaCO2: 103 mmHg and VR: 3.5; with the following set- tioned that most of the patients were highly recruitable tings: VT: 6 mL/Kg PBW, RR: 22/min, PEEP: 16 cmH2O, [4]. Mauri et al. reported in 10 intubated COVID-19 FiO2: 60%. Increasing respiratory rate from 22 to 35/ ARDS patients a large variability in potential for lung min was associated with a decrease in PaCO2 from 103 recruitment together with an elevated dead space frac- to 79 mmHg. Te patient was thereafter transferred to tion evaluated by electrical impedance tomography (EIT) another hospital because of the absence of biosafety [5]. level 3 laboratory in our center [15]. Such a respiratory During the initial epidemic in China, abnormal coag- pattern prompted us to plan to further precisely ana- ulation profles were observed in severe COVID-19 lyze the respiratory characteristics of other COVID-19 patients. D-dimers above 1000 ng/mL was an independ- ARDS patients admitted in the ICU. ent risk factor of in-hospital death [6]. In another study, Results were obtained thereafter between March 22, D-dimers were also correlated with mortality [7]. Te 2020 and March 30, 2020 in 22 consecutive COVID-19 hypothesis of microthrombosis was proposed since high ARDS patients without history of chronic respiratory levels of creatinine were associated with higher levels of disease. No patient was clinically suspected of pulmo- D-dimers (> 500 ng/mL), in favor of a microthrombotic nary embolism at the time of measurements. A prophy- origin for kidney failure [8]. lactic anticoagulation regimen (enoxaparin 40 mg once Endothelial damage at the microvascular level may daily subcutaneously) was administered. All patients thus play an important role not only in the incidence of were included in the French-COVID national cohort renal failure, but also for some aspects of the pathogen- after informed consent of proxies or family members esis of respiratory failure, beside alveolar insults. Indeed, by phone, due to quarantine. Additionally, proxies the SARS-CoV-2 receptor (ACE2) is strongly expressed or family members gave also an informed consent by in endothelial cells [9]. Since the lung accepts the whole phone for a formalized local process of collecting bio- of the cardiac output in its rich vascular and microvas- logical samples in relation to cardiovascular, metabolic cular bed, it could be therefore possible that infection or renal diseases (Comité de Protection des Personnes of endothelial cells could induce pulmonary endothelial Ile-De-France II, IRB registration 00001072, approval: lesions, triggering activation of coagulation. Accord- November 11, 2016). ingly, endothelial cells viral infection, pulmonary vascular While using a 5-cmH2O PEEP setting, 13 patients endothelialitis and pulmonary vascular microthrombo- fulflled the Berlin criteria for moderate ARDS and 9 sis are increasingly reported in autopsy studies [10–12]. patients for severe ARDS, with a median [IQR] PaO2/ Finally, based on an initial series of 40 COVID-19 hos- FiO2 value of 108 [87–134]. We therefore used a high- pitalized patients and on an independent cohort of 32 PEEP protective ventilation strategy, as part of our COVID-19 patients, we recently reported the interest respiratory bundle in ARDS patients [14]. We present of angiopoietin-2, a marker of endothelial activation, for measurements obtained early during the IMV course in predicting the need for ICU admission [13]. deeply sedated and paralyzed patients. Te CareScape Based on initial clinical fndings observed in a Covid-19 R860 ventilator (GE Healthcare, USA) was used, allow- ARDS patient in January 2020, we planned to systemati- ing the following measurements or calculations: cally investigate respiratory mechanics and gas exchanges in Covid-19 ARDS patients subsequently admitted to • Respiratory mechanics: plateau pressure (Pplateau), the medical ICU of the Georges Pompidou European total PEEP (PEEPtot), driving pressure (DP), res- Hospital. piratory system compliance (Crs), end-expiratory lung volume (EELV) as determined by the nitrogen Patients and methods washin–washout method. Study design and population • Gas exchanges: arterial blood gases, end-tidal A COVID-19 80-year-old patient without history of expired CO2 (ETCO2), PaO2/FiO2 ratio, alveolo- respiratory disease was placed on invasive mechani- arterial O2 diference (DAaO2), VR, physiological cal ventilation (IMV) after non-invasive ventilation dead space (VD/VT) as calculated by the respirator failure on Jan 27, 2020. After tracheal intubation, the using the Enghof–Bohr equation, O2 total body patient rapidly fulflled severe ARDS criteria. A high- uptake (VO2), CO2 total body production (VCO2). PEEP protective ventilation strategy was used, as part of our respiratory bundle [14]. While the respiratory We also obtained additional VD/VT measurements in patients in whom PEEP level was lowered of at least 5 system compliance was 25 mL/cmH2O and the PaO2/ cmH O within 4 days following initial measurements, FiO2 ratio 183 mmHg, the patient exhibited very high 2 when clinically indicated. Diehl et al. Ann. Intensive Care (2020) 10:95 Page 3 of 7 Laboratory confrmation of SARS‑CoV‑2 infection Results Nasopharyngeal swabs were collected in universal Among the 22 COVID-19 ARDS patients, 19 (86.4%) ® transport medium (Xpert nasopharyngeal sample were males with a median age of 65 [55–73] years. Sim- collection kit) at hospital admission. SARS-CoV-2 was plifed Acute Physiologic Score II (SAPSII) and Sequen- ™ detected using Allplex 2019-nCoV Assay (Seegene), tial Organ Failure Assessment (SOFA) scores were 55 a multiplex real-time PCR assay that detects three tar- [43–63] and 9 [7–11], respectively. Measurements were get genes (E gene, RdRP gene and N gene) in a single obtained 1 [1–4] day after intubation. Criteria for intu- tube. Data were automatically analyzed using Seegene bation followed French national guidelines [20]. Delay viewer software. Only qualitative data were available. between frst symptoms and tracheal intubation was 9 Broncho-alveolar lavage procedures were performed [7–11] days.
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