Introduction: Coronavirus disease 2019 (COVID-19) causes a hypercoagulable state. Several autopsy studies have found microthrombi in pulmonary circulation. Methods: In this randomized, open-label, phase II study, we randomized COVID-19 patients requiring mechanical ventilation to receive either therapeutic enoxaparin or the standard anticoagulant thromboprophylaxis. We evaluated the gas exchange over time through the ratio of partial pressure of arterial oxygen (PaO2) to the fraction of inspired oxygen (FiO2) at baseline, 7, and 14 days after randomization, the time until successful liberation from mechanical ventilation, and the ventilator-free days. Results: Ten patients were assigned to the therapeutic enoxaparin and ten patients to prophylactic anticoagulation. There was a statistically significant increase in the PaO2/FiO2 ratio over time in the therapeutic group (163 [95% confidence interval-CI 133-193] at baseline, 209 [95% CI 171-247] after 7 days, and 261 [95% CI 230-293] after 14 days), p = 0.0004. In contrast, we did not observe this improvement over time in the prophylactic group (184 [95% CI 146-222] at baseline, 168 [95% CI 142-195] after 7 days, and 195 [95% CI 128-262] after 14 days), p = 0.487. Patients of the therapeutic group had a higher ratio of successful liberation from mechanical ventilation (hazard ratio: 4.0 [95% CI 1.035-15.053]), p = 0.031 and more ventilator-free days (15 days [interquartile range IQR 6-16] versus 0 days [IQR 0-11]), p = 0.028 when compared to the prophylactic group. Conclusion: Therapeutic enoxaparin improves gas exchange and decreases the need for mechanical ventilation in severe COVID-19. Trial registration: REBEC RBR-949z6v.

Several autopsy studies showed microthrombi in pulmonary circulation of severe COVID-19 patients. The major limitation of these investigations is that the autopsy provided static information. Some of these alterations could be secondary to the disseminated intravascular coagulation (DIC) observed as the final standard route to the multisystem organ failure exhibited in critically ill patients. We report preliminary results of an in vivo evaluation of sublingual microcirculation in thirteen patients with severe COVID-19 requiring mechanical ventilation. We observed multiple filling defects moving within the microvessels indicative of thrombi in most of the cases 11/13 (85%). This is the first imaging documentation of microvascular thrombosis in living severe COVID-19 patients since the beginning of the hospitalization. The clinical relevance of microvascular thrombosis in this disease requires further research.

Several autopsies studies showed the presence of microthrombi in the pulmonary circulation of the severe COVID-19. The major limitation of these investigations is that the autopsy provided static information. Some of these alterations could be secondary to the disseminated intravascular coagulation (DIC) observed as the final common pathway of the multisystem organ failure exhibited in the critical patient. We report the preliminary results of an in vivo evaluation of the sublingual microcirculation in thirteen patients with severe COVID-19 requiring mechanical ventilation at the beginning of the hospitalization. They did not have any laboratorial DIC evidence. We observed multiple filling defects moving within the sublingual microvessels indicative of microthrombi in 11 (85%) patients. This is the first imaging documentation of microvascular thrombosis in living patients with severe COVID-19. The clinical relevance of microvascular thrombosis in this disease requires further research.

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