Microrheological aspects of severe COVID-19: relationship with anticoagulant therapy and possible disorders of the Fåhræus-Lindqvist effect, Мікрореологічні аспекти тяжкого перебігу COVID-19: взаємозв’язок із антикоагулянтною терапією та можливими порушеннями ефекту Фареуса — Ліндквіста

<jats:p>Background. Severe COVID-19 is characterized by endothelial dysfunction, immunothrombosis, and microvascular coagulopathy, which play a pivotal role in the development of multiple organ failure and increased mortality. Despite the widespread use of anticoagulant therapy, the optimal intensity of its use in critically ill patients remains controversial. Particular attention has been directed toward microrheological disturbances that may be associated with alterations in red blood cell parameters and impaired tissue perfusion. Objective: to evaluate the relationship between changes in hemogram parameters, hemostatic indices, and the intensity of anticoagulant therapy in patients with severe COVID-19, and to investigate the potential association between impaired blood microrheology and adverse clinical outcomes. Materials and methods. A retrospective study included 268 patients with severe COVID-19 who were treated in the intensive care unit of Bila Tserkva City Hospital 1 in 2021. They were divided into three groups according to the anticoagulant regimen: prophylactic-dose low-molecular-weight heparin (LMWH), therapeutic-dose LMWH, and escalated anticoagulation using LMWH combined with unfractionated heparin. Changes in hemoglobin, erythrocyte, platelet count, coagulation parameters, D-dimer levels, and clinical outcomes were evaluated. Statistical analysis was performed using SPSS Statistics version 26.0. Results. The use of prophylactic-dose anticoagulation was associated with the highest in-hospital mortality (90.8 %) and the most pronounced decline in hemoglobin, erythrocyte, and platelet levels during treatment. Transition to therapeutic and escalation anticoagulation regimens was associated with significant reductions in mortality to 61.9 and 41.2 %, respectively, along with better pre­servation of hematological parameters. These findings suggest a potential association between progressive microvascular coagulopathy, impaired blood microrheology, and unfavorable clinical outcomes. Conclusions. In patients with severe COVID-19, prophylactic-dose anticoagulation was associated with higher in-hospital mortality and unfavorable hematological dynamics compared to more intensive anticoagulation strategies. Progressive decreases in hemoglobin, erythrocyte, hematocrit, and platelet count may reflect the deve­lopment of microvascular coagulopathy and impaired microcirculation. The observed findings are consistent with the hypothesis that alterations in blood microrheology and mechanisms related to the Fåhræus-Lindqvist effect may contribute to disease progression; however, this concept requires confirmation in prospective studies employing direct assessment of microcirculation.</jats:p>