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      COVID-19, Hypercoagulability, and Cautiousness with Convalescent Plasma

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          To the Editor: We read with great interest the elegant study conducted by Patel and colleagues (1) regarding the alterations at pulmonary vessel level in patients with severe coronavirus disease (COVID-19). The authors meticulously presented the combination of physiologic data, the results of high-resolution imaging, and the hematologic observations in a cohort of 39 patients. They showed that the activation of inflammatory and coagulation pathways has a pivotal role in the development of acute respiratory failure induced by COVID-19, demonstrating the great impact of hypercoagulability and reduction of fibrinolysis on the pulmonary vasculature. Such a prothrombotic state finally induces pulmonary (and likely systemic) perfusion abnormalities, heavily contributing to the peculiar phenotype of COVID-19–induced respiratory failure (2). We believe that the results shown by Patel and colleagues (1), highlighting the presence of dilated peripheral lung vessels (roughly two-thirds of patients) and perfusion defects in all patients, are of great importance in cautiously interpreting the results of a recent study on the use of convalescent plasma (CP) in COVID-19. Indeed, this study evaluated the use of CP in more than 5,000 patients with severe or life-threatening COVID-19 (3) and prompted great (and in our opinion excessive) enthusiasm as the authors reported low incidence of serious adverse effects after CP. However, this safety endpoint was evaluated in a particularly short period of observation (4 h), which is far too limited to entirely account for subtle progression of an underlying hypercoagulability state. For instance, plasma is administered in the setting of hemorrhagic shock for its ability to improve hemostasis; thus, the idea of administering plasma to any patient with underlying hypercoagulability should be undertaken very watchfully. Depending on the methods for aiming at inactivating residual virus during the preparation of CP, the content of coagulation factors also may decrease, which would eventually blunt its procoagulant effects (4). However, in the presence of an already stimulated coagulation pathway as demonstrated by Patel and colleagues (1), even small amounts of residual coagulation factors in CP may potentiate the coagulation cascade in patients with COVID-19, representing a source of potential harm. In our opinion, the progression of thrombosis should not be evaluated only as evidence of new pulmonary embolism, but it may result in worsening oxygenations and gas exchanges. This could be the result of thrombosis and progression of perfusion defects with further dilatation of peripheral lung vessels. Moreover, considering the systemic impact of the underlying hypercoagulability, administration of CP may worsen perfusion in other vital organs, potentially increasing, among others, risks of myocardial and cerebral ischemia. Thus, great caution is warranted in looking for specific adverse events related to CP in patients with COVID-19. To add more uncertainty on the use of CP, its efficacy for the treatment of COVID-19 has been questioned by a Cochrane systematic review (5). Moreover, according to another recent meta-analysis of randomized controlled trials at low risk of bias, administration of CP to patients with severe influenza has not been shown to reduce mortality, number of days in the ICU, or number of days on mechanical ventilation (6). In summary, we think the results of the study of Patel and colleagues greatly contribute to the definition of pathogenesis and clinical characteristics of COVID-19, but they are also of great value when considering potential therapeutic strategies and the right approach to control for their safety. New studies on CP in patients with COVID-19 should be encouraged to report the methods of preparation for CP.

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          COVID-19 pneumonia: different respiratory treatments for different phenotypes?

          The Surviving Sepsis Campaign panel recently recommended that “mechanically ventilated patients with COVID-19 should be managed similarly to other patients with acute respiratory failure in the ICU [1].” Yet, COVID-19 pneumonia [2], despite falling in most of the circumstances under the Berlin definition of ARDS [3], is a specific disease, whose distinctive features are severe hypoxemia often associated with near normal respiratory system compliance (more than 50% of the 150 patients measured by the authors and further confirmed by several colleagues in Northern Italy). This remarkable combination is almost never seen in severe ARDS. These severely hypoxemic patients despite sharing a single etiology (SARS-CoV-2) may present quite differently from one another: normally breathing (“silent” hypoxemia) or remarkably dyspneic; quite responsive to nitric oxide or not; deeply hypocapnic or normo/hypercapnic; and either responsive to prone position or not. Therefore, the same disease actually presents itself with impressive non-uniformity. Based on detailed observation of several cases and discussions with colleagues treating these patients, we hypothesize that the different COVID-19 patterns found at presentation in the emergency department depend on the interaction between three factors: (1) the severity of the infection, the host response, physiological reserve and comorbidities; (2) the ventilatory responsiveness of the patient to hypoxemia; (3) the time elapsed between the onset of the disease and the observation in the hospital. The interaction between these factors leads to the development of a time-related disease spectrum within two primary “phenotypes”: Type L, characterized by Low elastance (i.e., high compliance), Low ventilation-to-perfusion ratio, Low lung weight and Low recruitability and Type H, characterized by High elastance, High right-to-left shunt, High lung weight and High recruitability. COVID-19 pneumonia, Type L At the beginning, COVID-19 pneumonia presents with the following characteristics: Low elastance. The nearly normal compliance indicates that the amount of gas in the lung is nearly normal [4]. Low ventilation-to-perfusion (VA/Q) ratio. Since the gas volume is nearly normal, hypoxemia may be best explained by the loss of regulation of perfusion and by loss of hypoxic vasoconstriction. Accordingly, at this stage, the pulmonary artery pressure should be near normal. Low lung weight. Only ground-glass densities are present on CT scan, primarily located subpleurally and along the lung fissures. Consequently, lung weight is only moderately increased. Low lung recruitability. The amount of non-aerated tissue is very low; consequently, the recruitability is low [5]. To conceptualize these phenomena, we hypothesize the following sequence of events: the viral infection leads to a modest local subpleural interstitial edema (ground-glass lesions) particularly located at the interfaces between lung structures with different elastic properties, where stress and strain are concentrated [6]. Vasoplegia accounts for severe hypoxemia. The normal response to hypoxemia is to increase minute ventilation, primarily by increasing the tidal volume [7] (up to 15–20 ml/kg), which is associated with a more negative intrathoracic inspiratory pressure. Undetermined factors other than hypoxemia markedly stimulate, in these patients, the respiratory drive. The near normal compliance, however, explains why some of the patients present without dyspnea as the patient inhales the volume he expects. This increase in minute ventilation leads to a decrease in PaCO2. The evolution of the disease: transitioning between phenotypes The Type L patients may remain unchanging for a period and then improve or worsen. The possible key feature which determines the evolution of the disease, other than the severity of the disease itself, is the depth of the negative intrathoracic pressure associated with the increased tidal volume in spontaneous breathing. Indeed, the combination of a negative inspiratory intrathoracic pressure and increased lung permeability due to inflammation results in interstitial lung edema. This phenomenon, initially described by Barach in [8] and Mascheroni in [9] both in an experimental setting, has been recently recognized as the leading cause of patient self-inflicted lung injury (P-SILI) [10]. Over time, the increased edema increases lung weight, superimposed pressure and dependent atelectasis. When lung edema reaches a certain magnitude, the gas volume in the lung decreases, and the tidal volumes generated for a given inspiratory pressure decrease [11]. At this stage, dyspnea develops, which in turn leads to worsening P-SILI. The transition from Type L to Type H may be due to the evolution of the COVID-19 pneumonia on one hand and the injury attributable to high-stress ventilation on the other. COVID-19 pneumonia, Type H The Type H patient: High elastance. The decrease in gas volume due to increased edema accounts for the increased lung elastance. High right-to-left shunt. This is due to the fraction of cardiac output perfusing the non-aerated tissue which develops in the dependent lung regions due to the increased edema and superimposed pressure. High lung weight. Quantitative analysis of the CT scan shows a remarkable increase in lung weight (> 1.5 kg), on the order of magnitude of severe ARDS [12]. High lung recruitability. The increased amount of non-aerated tissue is associated, as in severe ARDS, with increased recruitability [5]. The Type H pattern, 20–30% of patients in our series, fully fits the severe ARDS criteria: hypoxemia, bilateral infiltrates, decreased the respiratory system compliance, increased lung weight and potential for recruitment. Figure 1 summarizes the time course we described. In panel a, we show the CT in spontaneous breathing of a Type L patient at admission, and in panel b, its transition in Type H after 7 days of noninvasive support. As shown, a similar degree of hypoxemia was associated with different patterns in lung imaging. Fig. 1 a CT scan acquired during spontaneous breathing. The cumulative distribution of the CT number is shifted to the left (well-aerated compartments), being the 0 to − 100 HU compartment, the non-aerated tissue virtually 0. Indeed, the total lung tissue weight was 1108 g, 7.8% of which was not aerated and the gas volume was 4228 ml. Patient receiving oxygen with venturi mask inspired oxygen fraction of 0.8. b CT acquired during mechanical ventilation at end-expiratory pressure at 5 cmH2O of PEEP. The cumulative distribution of the CT scan is shifted to the right (non-aerated compartments), while the left compartments are greatly reduced. Indeed, the total lung tissue weight was 2744 g, 54% of which was not aerated and the gas volume was 1360 ml. The patient was ventilated in volume controlled mode, 7.8 ml/kg of tidal volume, respiratory rate of 20 breaths per minute, inspired oxygen fraction of 0.7 Respiratory treatment Given this conceptual model, it follows that the respiratory treatment offered to Type L and Type H patients must be different. The proposed treatment is consistent with what observed in COVID-19, even though the overwhelming number of patients seen in this pandemic may limit its wide applicability. The first step to reverse hypoxemia is through an increase in FiO2 to which the Type L patient responds well, particularly if not yet breathless. In Type L patients with dyspnea, several noninvasive options are available: high-flow nasal cannula (HFNC), continuous positive airway pressure (CPAP) or noninvasive ventilation (NIV). At this stage, the measurement (or the estimation) of the inspiratory esophageal pressure swings is crucial [13]. In the absence of the esophageal manometry, surrogate measures of work of breathing, such as the swings of central venous pressure [14] or clinical detection of excessive inspiratory effort, should be assessed. In intubated patients, the P0.1 and P occlusion should also be determined. High PEEP, in some patients, may decrease the pleural pressure swings and stop the vicious cycle that exacerbates lung injury. However, high PEEP in patients with normal compliance may have detrimental effects on hemodynamics. In any case, noninvasive options are questionable, as they may be associated with high failure rates and delayed intubation, in a disease which typically lasts several weeks. The magnitude of inspiratory pleural pressures swings may determine the transition from the Type L to the Type H phenotype. As esophageal pressure swings increase from 5 to 10 cmH2O—which are generally well tolerated—to above 15 cmH2O, the risk of lung injury increases and therefore intubation should be performed as soon as possible. Once intubated and deeply sedated, the Type L patients, if hypercapnic, can be ventilated with volumes greater than 6 ml/kg (up to 8–9 ml/kg), as the high compliance results in tolerable strain without the risk of VILI. Prone positioning should be used only as a rescue maneuver, as the lung conditions are “too good” for the prone position effectiveness, which is based on improved stress and strain redistribution. The PEEP should be reduced to 8–10 cmH2O, given that the recruitability is low and the risk of hemodynamic failure increases at higher levels. An early intubation may avert the transition to Type H phenotype. Type H patients should be treated as severe ARDS, including higher PEEP, if compatible with hemodynamics, prone positioning and extracorporeal support. In conclusion, Type L and Type H patients are best identified by CT scan and are affected by different pathophysiological mechanisms. If not available, signs which are implicit in Type L and Type H definition could be used as surrogates: respiratory system elastance and recruitability. Understanding the correct pathophysiology is crucial to establishing the basis for appropriate treatment.
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            Pulmonary Angiopathy in Severe COVID-19: Physiologic, Imaging, and Hematologic Observations

            Rationale: Clinical and epidemiologic data in coronavirus disease (COVID-19) have accrued rapidly since the outbreak, but few address the underlying pathophysiology. Objectives: To ascertain the physiologic, hematologic, and imaging basis of lung injury in severe COVID-19 pneumonia. Methods: Clinical, physiologic, and laboratory data were collated. Radiologic (computed tomography (CT) pulmonary angiography [n = 39] and dual-energy CT [DECT, n = 20]) studies were evaluated: observers quantified CT patterns (including the extent of abnormal lung and the presence and extent of dilated peripheral vessels) and perfusion defects on DECT. Coagulation status was assessed using thromboelastography. Measurements and Results: In 39 consecutive patients (male:female, 32:7; mean age, 53 ± 10 yr [range, 29–79 yr]; Black and minority ethnic, n = 25 [64%]), there was a significant vascular perfusion abnormality and increased physiologic dead space (dynamic compliance, 33.7 ± 14.7 ml/cm H2O; Murray lung injury score, 3.14 ± 0.53; mean ventilatory ratios, 2.6 ± 0.8) with evidence of hypercoagulability and fibrinolytic “shutdown”. The mean CT extent (±SD) of normally aerated lung, ground-glass opacification, and dense parenchymal opacification were 23.5 ± 16.7%, 36.3 ± 24.7%, and 42.7 ± 27.1%, respectively. Dilated peripheral vessels were present in 21/33 (63.6%) patients with at least two assessable lobes (including 10/21 [47.6%] with no evidence of acute pulmonary emboli). Perfusion defects on DECT (assessable in 18/20 [90%]) were present in all patients (wedge-shaped, n = 3; mottled, n = 9; mixed pattern, n = 6). Conclusions: Physiologic, hematologic, and imaging data show not only the presence of a hypercoagulable phenotype in severe COVID-19 pneumonia but also markedly impaired pulmonary perfusion likely caused by pulmonary angiopathy and thrombosis.
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              Convalescent plasma or hyperimmune immunoglobulin for people with COVID-19: a rapid review

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                Author and article information

                Journal
                Am J Respir Crit Care Med
                Am J Respir Crit Care Med
                ajrccm
                American Journal of Respiratory and Critical Care Medicine
                American Thoracic Society
                1073-449X
                1535-4970
                15 January 2021
                15 January 2021
                15 January 2021
                15 January 2021
                : 203
                : 2
                : 257-258
                Affiliations
                [ 1 ]Azienda Ospedaliero Universitaria “Policlinico-Vittorio Emanuele”

                Catania, Italy

                and
                [ 2 ]University of Catania

                Catania, Italy
                Author notes
                [* ]Corresponding author (e-mail: filipposanfi@ 123456yahoo.it ).
                Article
                202008-3139LE
                10.1164/rccm.202008-3139LE
                7874424
                33085908
                9b9ef8e8-344d-4aaf-933d-24ebd3053bf8
                Copyright © 2021 by the American Thoracic Society

                This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 ( http://creativecommons.org/licenses/by-nc-nd/4.0/). For commercial usage and reprints, please contact Diane Gern ( dgern@ 123456thoracic.org ).

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