Optimizing Lower Extremity Duplex Ultrasound Screening After Traumatic Injury

Direct red blood cell effect on thrombosis is dependent on the interaction of tissue factor and calcium with membrane phosphatidylserine

BACKGROUND

Prior literature has implicated red blood cells (RBCs) in the initiation of thrombosis and suggests that posttransfusion hypercoagulability may occur secondary to the effects of RBCs. Elevated serum tissue factor is a known sequelae of acute trauma. Phosphatidylserine (PS) is a prothrombotic phospholipid present within the RBC cell membrane. We hypothesized that RBC aggregation is dependent on the interaction between RBC membrane bound (exposed) PS, extracellular calcium, and tissue factor.

METHODS

Human whole blood (WB) was separated into components, including RBCs and platelet-rich plasma (PRP). Whole blood, PRP, and RBCs underwent impedance aggregometry utilizing arachidonic acid (AA), ADP, collagen, calcium, and tissue factor (TF)-based agonists. Red blood cells then underwent impedance aggregometry utilizing combined calcium and TF agonists. Red blood cells were pretreated with Annexin V, a known PS blocking agent, and underwent impedance aggregometry with combined calcium and TF agonists to determine if the mechanism of calcium/TF-induced RBC aggregability is dependent on PS. Red blood cells treated with calcium, TF, calcium+TF, and pre-treated with Annexin V followed by calcium+TF were perfused through an in vitro model of pulmonary microcirculatory flow.

RESULTS

Red blood cell aggregation was significantly higher than that of WB and PRP when utilizing a TF agonist, an effect unique to TF. The combination of calcium and TF demonstrated significantly higher RBC aggregation than either agonist alone. Pretreatment with Annexin V resulted in a significantly reduced aggregability of RBC following treatment with TF + calcium. Red blood cells aged to 42 days did not exhibit significant change in aggregation. Exposure to calcium and TF significantly reduced time to thrombosis of RBCs perfused through a pulmonary microcirculatory model.

CONCLUSION

Treatment with both TF and calcium synergistically induces RBC aggregation. Phosphatidylserine appears to play an integral role in the TF/calcium-based, age-independent RBC aggregation response. Red blood cells treated with TF + calcium exhibit more rapid thrombus formation in an in vitro model of pulmonary microcirculatory perfusion.

Haemostasis and Inflammatory Parameters as Potential Diagnostic Biomarkers for VTE in Trauma-Immobilized Patients

Venous thromboembolism (VTE), which encompasses deep venous thrombosis (DVT) and pulmonary embolism (PE), is a major public health concern due to its high incidences of morbidity and mortality. Patients who have experienced trauma with prolonged immobilization are at an increased risk of developing VTE. Plasma D-dimer levels have been known to be elevated in trauma patients, and they were closely correlated with the number of fractures. In other words, plasma D-dimer levels cannot be used as the only indicator of VTE in trauma cases. Given the limitations, further study is needed to explore other potential biomarkers for diagnosing VTE. To date, various established and novel VTE biomarkers have been studied in terms of their potential for predicting VTE, diagnostic performance, and improving clinical therapy for VTE. Therefore, this review aims to provide information regarding classic and essential haemostasis (including prothrombin time (PT), activated partial thromboplastin time (aPTT), D-dimer, fibrinogen, thrombin generation, protein C, protein S, antithrombin, tissue factor pathway inhibitor, and platelet count) and inflammatory biomarkers (C-reactive protein, erythrocyte sedimentation rate, and soluble P-selectin) as potential diagnostic biomarkers that can predict the risk of VTE development among trauma patients with prolonged immobilization. Thus, further advancement in risk stratification using these biomarkers would allow for a better diagnosis of patients with VTE, especially in areas with limited resources.

The Utility of Lower Extremity Screening Duplex for The Detection of Deep Vein Thrombosis in Trauma

BACKGROUND

Trauma patients are high-risk for venous thromboembolism (VTE). Lower extremity screening duplex ultrasonography (LESDUS) is controversial and not standardized for early VTE diagnosis. By implementing risk stratification and selective screening, we aim to optimize resource utilization.

MATERIALS AND METHODS

A retrospective review were conducted at a Level-1 Trauma Center, January 2015-October 2019. LESDUS was performed within 72-h of presentation, then weekly. Demographics, VTE data, and outcomes were collected from the trauma registry. Risk assessment profile (RAP) score was calculated based on collected data.

RESULTS

Of 5,645 patients included, 2,813 (49.8%) were screened for lower extremity deep vein thrombosis (LEDVT). Of 187 patients with LEDVT, 154 were diagnosed on LESDUS, 18 after negative LESDUS, and 15 in unscreened patients. Patients with VTE were older (61y versus 55, P < 0.01), more often male (70.9% versus 29.1%, P = 0.03), had higher ISS (16 versus 10, P < 0.01), longer hospital length of stay (LOS) (11.5 d versus 3, P < 0.01), longer ICU LOS (4.5 d versus 1, P < 0.01), and increased mortality (9.1% versus 4.3%, P = 0.01). RAP was higher in VTE patients versus those without (nine versus three, P < 0.01). RAP ≥8 was 62.5% sensitive and 70.4% specific for VTE. Chemoprophylaxis delay also correlated with increased VTE (OR = 1.48, 95% CI = 1.03-2.12).

CONCLUSIONS

VTE remains a significant complication in trauma patients. Despite a universal LESDUS protocol, only 50% of patients underwent screening and 20% of all LE DVTs were not identified on LESDUS. To optimize resource utilization and protocol adherence, LESDUS should only be performed if RAP ≥8 or if unable to administer timely chemoprophylaxis.

Impact of antithrombin III and enoxaparin dosage adjustment on prophylactic anti-Xa concentrations in trauma patients at high risk for venous thromboembolism: a randomized pilot trial

The impact of antithrombin III activity (AT-III) on prophylactic enoxaparin anti-factor Xa concentration (anti-Xa) is unknown in high-risk trauma patients. So too is the optimal anti-Xa-adjusted enoxaparin dosage. This prospective, randomized, pilot study sought to explore the association between AT-III and anti-Xa goal attainment and to preliminarily evaluate two enoxaparin dosage adjustment strategies in patients with subprophylactic anti-Xa. Adult trauma patients with Risk Assessment Profile (RAP) ≥ 5 prescribed enoxaparin 30 mg subcutaneously every 12 h were eligible. AT-III and anti-Xa were drawn 8 h after the third enoxaparin dose and compared between patients with anti-Xa ≥ 0.1 IU/mL (goal; control group) or anti-Xa < 0.1 IU/mL (subprophylactic; intervention group). The primary outcome was difference in baseline AT-III. Subsequently, intervention group patients underwent 1:1 randomization to either enoxaparin 40 mg every 12 h (up to 50 mg every 12 h if repeat anti-Xa < 0.1 IU/mL) (enox12) or enoxaparin 30 mg every 8 h (enox8) with repeat anti-Xa assessments. The proportion of patients achieving goal anti-Xa after dosage adjustment were compared. A total of 103 patients were included. Anti-Xa was subprophylactic in 50.5%. Baseline AT-III (median [IQR]) was 87% [80-98%] in control patients versus 82% [71-96%] in intervention patients (p = 0.092). Goal trough anti-Xa was achieved on first assessment in 38.1% enox12 versus 50% enox8 patients (p = 0.67), 84.6% versus 53.3% on second assessment (p = 0.11), and 100% vs. 54.5% on third trough assessment (p = 0.045). AT-III activity did not differ between high-risk trauma patients with goal and subprophylactic enoxaparin anti-Xa concentrations, although future investigation is warranted. Enoxaparin dose adjustment rather than frequency adjustment may be associated with a higher proportion of patients achieving goal anti-Xa over time.

Trauma patients at risk for venous thromboembolism who undergo routine duplex ultrasound screening experience fewer pulmonary emboli: A prospective randomized trial

BACKGROUND

Although guidelines are established for the prevention and management of venous thromboembolism (VTE) in trauma, no consensus exists regarding protocols for the diagnostic approach. We hypothesized that at-risk trauma patients who undergo duplex ultrasound (DUS) surveillance for lower extremity deep venous thrombosis (DVT) will have a lower rate of symptomatic or fatal pulmonary embolism (PE) than those who do not undergo routine surveillance.

METHODS

Prospective, randomized trial between March 2017 and September 2019 of trauma patients admitted to a single, level 1 trauma center, with a risk assessment profile score of ≥5. Patients were randomized to receive either bilateral lower extremity DUS surveillance on days 1, 3, and 7 and weekly during hospitalization ultrasound group (US) or no surveillance no ultrasound group (NoUS). Rates of in-hospital and 90-day DVT and PE were reported as was DVT propagation and all-cause mortality. Standard care for the prevention and management of VTE per established institutional protocols was provided to all patients.

RESULTS

A total of 3,236 trauma service admissions were screened, and 1,989 moderate- and high-risk patients were randomized (US, 995; NoUS, 994). The mean ± SD age was 62 ± 20.1 years, Injury Severity Score was 14 ± 9.7, risk assessment profile was 7.1 ± 2.4, and 97% suffered blunt trauma. There was no difference in demographics or VTE risk factors between the groups. There were significantly fewer in-hospital PE in the US group than the NoUS group (1 [0.1%] vs. 9 [0.9%], p = 0.01). The US group experienced more in-hospital below-knee DVTs (124 [12.5%] vs. 8 [0.8%], p < 0.001) and above-knee DVTs (19 [1.9%] vs. 8 [0.8%], p = 0.05). There was no difference in 90-day PE or DVT, or overall mortality.

CONCLUSION

The implementation of a selective routine DUS protocol was associated with significantly fewer in-hospital PE. More DVTs were identified with routine screening; however, surveillance bias appears to exist primarily with distal DVT. Larger trials are needed to further characterize the relationship between routine DUS screening and VTE outcomes in the high-risk trauma population.

LEVEL OF EVIDENCE

Therapeutic/care management, level II.

Impact of Weight on Anti-Xa Attainment in High-Risk Trauma Patients on Enoxaparin Chemoprophylaxis

BACKGROUND

Serum anti-factor Xa (anti-Xa) concentration may guide low molecular weight heparin chemoprophylaxis in trauma patients. Higher total body weight (TBW) is a risk factor for subprophylactic anti-Xa and venous thromboembolism (VTE). The purpose of this study was to evaluate TBW differences in patients with subprophylactic versus prophylactic trough anti-Xa.

METHODS

This retrospective study included adults admitted to the trauma service who received enoxaparin chemoprophylaxis, trough anti-Xa assessment, and screening duplex ultrasound. Initial enoxaparin dose was determined per trauma team weight-tiered protocol with subsequent 10 mg increase if anti-Xa was subprophylactic. Patients were stratified into subprophylactic (anti-Xa <0.1 IU/ml) and prophylactic (anti-Xa ≥0.1 IU/mL) groups. The primary outcome was difference in TBW. Secondary outcomes were weight-adjusted enoxaparin dose (mg/kg), VTE, red blood cell (pRBC) transfusions.

RESULTS

A total of 887 patients were included with 681 (76.8%) having subprophylactic anti-Xa. The subprophylactic group had significantly younger age, higher proportion male sex, higher Injury Severity Score (ISS), higher BMI, and longer length of hospital stay. The subprophylactic group had higher TBW (median [IQR], 87.8 [74-102] kg vs. 78.9 [68-91.8] kg; P < 0.001) which equated to a lower weight-adjusted dose (0.34 [0.3-0.41] mg/kg vs. 0.38 (0.33-0.44) mg/kg; P < 0.001). There were no differences in VTE (10.4% vs. 9.2%; P = 0.71) or pRBC administration (17.0% vs. 16.0%; P = 0.81).

CONCLUSIONS

TBW is higher and weight-adjusted enoxaparin dose is lower in high-risk trauma patients with subprophylactic anti-Xa concentrations. These data suggest TBW should be considered when determining the optimal prophylactic enoxaparin dose in high-risk trauma patients.