Increased histone-DNA complexes and endothelial-dependent thrombin generation in severe COVID-19.

Coagulopathy in severe COVID-19 is common but poorly understood. The purpose of this study was to determine how SARS-CoV-2 infection impacts histone levels, fibrin structure, and endogenous thrombin potential in the presence and absence of endothelial cells. We studied individuals with SARS-CoV-2 infection and acute respiratory distress syndrome at the time of initiation of mechanical ventilation compared to healthy controls. Circulating histone-DNA complexes were elevated in the plasma of COVID-19 patients relative to healthy controls (n=6, each group). Using calibrated automated thrombography, thrombin generation was altered in COVID-19 patient plasma samples. Despite having increased endogenous thrombin potential, patient plasma samples exhibited prolonged lag times and times to peak thrombin in the presence of added tissue factor and PCPS. Strikingly different results were observed when endothelial cells were used in place of tissue factor and PCPS. While healthy control plasma samples did not generate measurable thrombin after 60 min, plasma samples from COVID-19+ patients formed thrombin (mean lag time ~20 min). Consistent with the observed alterations in thrombin generation, clots from COVID-19 subjects exhibited a denser fibrin network, thinner fibers and lower fibrin resolvability. Elevated histones, aberrant fibrin formation, and increased endothelial-dependent thrombin generation may contribute to coagulopathy in COVID-19.

Dense and dangerous: The tissue plasminogen activator-resistant fibrinolysis shutdown phenotype is due to abnormal fibrin polymerization.

BACKGROUND: Both hyperfibrinolysis and fibrinolysis shutdown can occur after severe trauma. The subgroup of trauma patients with fibrinolysis shutdown resistant to tissue plasminogen activator (t-PA)-mediated fibrinolysis have increased mortality. Fibrin polymerization and structure may influence fibrinolysis subgroups in trauma, but fibrin architecture has not been characterized in acutely injured subjects. We hypothesized that fibrin polymerization measured in situ will correlate with fibrinolysis subgroups. METHODS: Blood samples were collected from trauma patients and noninjured controls. We selected samples across a range of fibrinolysis phenotypes (shutdown, physiologic, hyperfibrinolysis) and t-PA sensitivities (sensitive, physiologic, resistant) determined by thrombelastography. Plasma clots were created in situ with fluorescent fibrinogen and imaged using confocal microscopy for analysis of clot architecture in three dimensions. For each clot, we quantified the fiber resolvability, a metric of fiber distinctness or clarity, by mapping the variance of fluorescence intensity relative to background fluorescence. We also determined clot porosity by measuring the size and distribution of the gaps between fibrin fibers in three-dimensional space. We compared these measures across fibrinolysis subgroups. RESULTS: Fiber resolvability was significantly lower in all trauma subgroups compared with controls (n = 35 and 5, respectively; p < 0.05). We observed markedly different patterns of fibrin architecture among trauma patients stratified by fibrinolysis subgroup. Subjects with t-PA-resistant fibrinolysis shutdown exhibited abnormal, densely packed fibrin clots nearly devoid of pores. Individuals with t-PA-hypersensitive fibrinolysis shutdown had highly irregular clots with pores as large as 2500 µm to 20,000 µm, versus 78 µm to 1250 µm in noninjured controls. CONCLUSION: Fiber resolvability was significantly lower in trauma patients than controls, and subgroups of fibrinolysis differ in the porosity of the fibrin clot structure. The dense fibrin network in the t-PA-resistant group may prevent access to plasmin, suggesting a mechanism for thrombotic morbidity after injury.

Diagnostic Performance of Carbon Monoxide Testing by Pulse Oximetry in the Emergency Department.

BACKGROUND: Carbon monoxide (CO) exposure causes roughly 40,000 emergency department (ED) visits annually and is commonly misdiagnosed. Whereas the standard method of carboxyhemoglobin (HbCO) measurement utilizes blood gas analysis, a noninvasive, FDA-cleared alternative exists. We evaluated the performance of pulse oximetry (SpCO) for identification of CO exposure in ED patients. METHODS: We compared pulse oximetry to blood HbCO levels in a prospective observational study of adult and pediatric subjects recruited from the ED. Nurses screened a convenience sample of patients and referred those with SpCO ≥ 10% to research staff. Researchers also approached individuals who presented with signs and symptoms of CO toxicity. We determined diagnostic performance with a Bland-Altman analysis and calculated sensitivity and specificity for detection of elevated HbCO at thresholds of ≥ 10% and ≥ 15%. To optimize the potential sensitivity of SpCO for detection of CO toxicity, research technicians performed 3 SpCO readings within 5 min of the blood draw for laboratory measurement. A positive SpCO test was defined as any SpCO ≥ 10%. RESULTS: 42,000 patients were screened, 212 were evaluated, and 126 subjects were enrolled. Median HbCO level was 6% (range 1.6-21.9%). Limits of agreement were -10.3% and 8.1%. Of 23 individuals with elevated HbCO ≥ 10%, 13 were not suspected based on clinical assessment. Critically elevated HbCO was present in 6 individuals. Based on our a priori threshold of 10% for a positive test, pulse oximetry identified 14 of 23 subjects with HbCO ≥ 10%, with a sensitivity of 61% (95% CI 39-80%) and a specificity of 86% (95% CI 78-92%), and 5 of 6 subjects with HbCO ≥ 15%, with a sensitivity of 83% (95% CI 36-100%) and a specificity of 81% (95% CI 73-87%). CONCLUSIONS: Pulse oximetry underestimated HbCO and produced false negative results (ie, SpCO < 10% for all three measurements) in 17% of ED subjects with elevated HbCO ≥ 15%. Triage screening with pulse oximetry detected cases of elevated HbCO that were not suspected by the clinical provider.

Accuracy of Point-of-Care Testing for Anemia in the Emergency Department.

BACKGROUND: Pulse oximetry has become the standard of care in emergency medicine, operating rooms, and medical wards for the monitoring of oxygenation, but the use of pulse oximetry for assessment of hemoglobin (Hb) is controversial. The purpose of this study was to compare the accuracy and precision of 2 point-of-care Hb measurement devices, the Pronto-7 and the HemoCue 201+, to laboratory testing. METHODS: We studied a convenience sample of patients in the emergency department who required a complete blood count. We excluded patients in critical condition or those with elevated methemoglobin, impaired perfusion, or finger deformities. Each subject provided 2 capillary samples for measurement with the HemoCue 201+ and 2 consecutive readings with the Pronto-7. We used Bland-Altman analysis to compare the performance of the point-of-care devices to laboratory measurements. We also determined the diagnostic performance for the detection of anemia by sex (Hb < 11.6 g/dL for females, Hb < 13.8 g/dL for males). RESULTS: 201 of the 350 subjects enrolled (57%) were female. Mean (SD) age was 50.9 (19.0) y. Complete data were available for 297 (84.9%) of the Pronto-7 readings and 323 (92.3%) of the HemoCue 201+ readings. Mean (SD) laboratory Hb was 13.1 g/dL (2.3). Mean bias (Bland-Altman limits of agreement) for the Pronto-7 was -0.52 g/dL (-3.29 to 2.25), and for the HemoCue 201+ the mean bias was -0.98 g/dL (-3.57 to 1.61). Sensitivity and specificity for diagnosis of anemia were 81.6% (95% CI 72.5-88.7) and 75.4% (95% CI 68.8-81.1) for the Pronto-7 and 99.1% (95% CI 94.8-100.0) and 71.0% (95% CI 64.4-76.9) for HemoCue 201+. CONCLUSION: Both devices provided clinically useful methods to screen for anemia.