TBI risk stratification at presentation: A prospective study of the incidence and timing of radiographic worsening in the Parkland Protocol

Early venous thromboembolism chemoprophylaxis in traumatic brain injury requiring neurosurgical intervention: Safe and effective

BACKGROUND

Traumatic brain injury patients who require neurosurgical intervention are at the highest risk of worsening intracranial hemorrhage. This subgroup of patients has frequently been excluded from prior research regarding the timing of venous thromboembolism chemoprophylaxis. This study aims to assess the efficacy and safety of early venous thromboembolism chemoprophylaxis in patients with traumatic brain injuries requiring neurosurgical interventions.

METHODS

This is a single-center retrospective review (2016-2020) of traumatic brain injury patients requiring neurosurgical intervention admitted to a level I trauma center. Interventions included intracranial pressure monitoring, subdural drain, external ventricular drain, craniotomy, and craniectomy. Exclusion criteria included neurosurgical intervention after chemoprophylaxis initiation, death within 5 days of admission, and absence of chemoprophylaxis. The total population was stratified into Early (≤72 hours of intervention) versus Late (>72 hours after intervention) chemoprophylaxis initiation.

RESULTS

A total of 351 patients met the inclusion criteria, of whom 204 (58%) had early chemoprophylaxis initiation. Overall, there were no significant differences in baseline and admission characteristics between cohorts. The Early chemoprophylaxis cohort had a statistically significant lower venous thromboembolism rate (5% vs 13%, P < .001) with no increased risk of worsening intracranial hemorrhage (10% vs 13%, P = .44) or neurosurgical reintervention (8% vs 10%, P = .7). On subgroup analysis, a total of 169 patients required either a craniotomy or a craniectomy before chemoprophylaxis. The Early chemoprophylaxis cohort had statistically significant lower venous thromboembolism rates (2% vs 11%, P < .001) with no increase in intracranial hemorrhage (8% vs 11%, P = .6) or repeat neurosurgical intervention (8% vs 10%, P = .77).

CONCLUSION

Venous thromboembolism prophylaxis initiation within 72 hours of neurosurgical intervention is safe and effective. Further prospective research is warranted to validate the results of this study.

Saudi Critical Care Society clinical practice guidelines on the prevention of venous thromboembolism in adults with trauma: reviewed for evidence-based integrity and endorsed by the Scandinavian Society of Anaesthesiology and Intensive Care Medicine

BACKGROUND

To develop evidence-based clinical practice guidelines on venous thromboembolism (VTE) prevention in adults with trauma in inpatient settings.

METHODS

The Saudi Critical Care Society (SCCS) sponsored guidelines development and included 22 multidisciplinary panel members who completed conflict-of-interest forms. The panel developed and answered structured guidelines questions. For each question, the literature was searched for relevant studies. To summarize treatment effects, meta-analyses were conducted or updated. Quality of evidence was assessed using the Grading Recommendations, Assessment, Development, and Evaluation (GRADE) approach, then the evidence-to-decision (EtD) framework was used to generate recommendations. Recommendations covered the following prioritized domains: timing of pharmacologic VTE prophylaxis initiation in non-operative blunt solid organ injuries; isolated blunt traumatic brain injury (TBI); isolated blunt spine trauma or fracture and/or spinal cord injury (SCI); type and dose of pharmacologic VTE prophylaxis; mechanical VTE prophylaxis; routine duplex ultrasonography (US) surveillance; and inferior vena cava filters (IVCFs).

RESULTS

The panel issued 12 clinical practice recommendations-one, a strong recommendation, 10 weak, and one with no recommendation due to insufficient evidence. The panel suggests starting early pharmacologic VTE prophylaxis for non-operative blunt solid organ injuries, isolated blunt TBIs, and SCIs. The panel suggests using low molecular weight heparin (LMWH) over unfractionated heparin (UFH) and suggests either intermediate-high dose LMWH or conventional dosing LMWH. For adults with trauma who are not pharmacologic candidates, the panel strongly recommends using mechanical VTE prophylaxis with intermittent pneumatic compression (IPC). The panel suggests using either combined VTE prophylaxis with mechanical and pharmacologic methods or pharmacologic VTE prophylaxis alone. Additionally, the panel suggests routine bilateral lower extremity US in adults with trauma with elevated risk of VTE who are ineligible for pharmacologic VTE prophylaxis and suggests against the routine placement of prophylactic IVCFs. Because of insufficient evidence, the panel did not issue any recommendation on the use of early pharmacologic VTE prophylaxis in adults with isolated blunt TBI requiring neurosurgical intervention.

CONCLUSION

The SCCS guidelines for VTE prevention in adults with trauma were based on the best available evidence and identified areas for further research. The framework may facilitate adaptation of recommendations by national/international guideline policymakers.

Association of Venous Thromboembolism Prophylaxis After Neurosurgical Intervention for Traumatic Brain Injury With Thromboembolic Complications, Repeated Neurosurgery, and Mortality

Importance

There is a lack of evidence regarding the effectiveness and safety of pharmacologic venous thromboembolism (VTE) prophylaxis among patients who undergo neurosurgical interventions for traumatic brain injury (TBI).

Objective

To measure the association between timing of VTE prophylaxis after urgent neurosurgical intervention for TBI and thromboembolic and intracranial complications.

Design, Setting, and Participants

This retrospective cohort study included adult patients (aged ≥16 years) who underwent urgent neurosurgical interventions (craniotomy/craniectomy or intracranial monitor/drain insertion within 24 hours after admission) for TBI at level 1 and 2 trauma centers participating in the American College of Surgeons Trauma Quality Improvement Program between January 1, 2012, and December 31, 2016. Data were analyzed from January to August 2020.

Exposures

Timing of pharmacologic VTE prophylaxis initiation after urgent neurosurgical intervention (prophylaxis delay) measured in days (24-hour periods).

Main Outcomes and Measures

The primary outcome was VTE (deep vein thrombosis or pulmonary embolism). Secondary outcomes were repeated neurosurgery (neurosurgical reintervention after initiation of VTE prophylaxis) and mortality. Hierarchical logistic regression models were used to evaluate the association between prophylaxis delay and each outcome at the patient level and were adjusted for patient baseline and injury characteristics.

Results

The study included 4951 patients (3676 [74%] male; median age, 50 years [IQR, 31-64 years]) who underwent urgent neurosurgical intervention for TBI at 304 trauma centers. The median prophylaxis delay was 3 days (IQR, 1-5 days). After adjustment for patient baseline and injury characteristics, prophylaxis delay was associated with increased odds of VTE (adjusted odds ratio [aOR], 1.08 per day; 95% CI, 1.04-1.12). Earlier initiation of prophylaxis was associated with increased risk of repeated neurosurgery. During the first 3 days, each additional day of prophylaxis delay was associated with a 28% decrease in odds of repeated neurosurgery (aOR, 0.72 per day; 95% CI, 0.59-0.88). After 3 days, each additional day of prophylaxis delay was associated with an additional 15% decrease in odds of repeated neurosurgery (aOR, 0.85 per day; 95% CI, 0.80-0.90). Earlier prophylaxis was associated with greater mortality among patients who initially underwent intracranial monitor/drain procedures, such that each additional day of prophylaxis delay was associated with decreased odds of death (aOR, 0.94 per day; 95% CI, 0.89-0.99).

Conclusions and Relevance

In this cohort study of patients who underwent urgent neurosurgical interventions for TBI, early pharmacologic VTE prophylaxis was associated with reduced risk of thromboembolism. However, earlier initiation of prophylaxis was associated with increased risk of repeated neurosurgery. These findings suggest that although timely initiation of prophylaxis should be prioritized, caution should be used particularly during the first 3 days after the index procedure, when this risk appears to be highest.

Progression of Intracranial Hemorrhage After Chemical Prophylaxis Using Low-Molecular-Weight Heparin in Patients With Traumatic Brain Injury

INTRODUCTION

Chemical prophylaxis using low-molecular-weight heparin (LMWH) is considered a standard of care for venous thromboembolism in trauma patients. Our center performs a head computed tomography (CT) scan 24 hours after initiation with prophylactic LMWH in the setting of a known traumatic brain injury (TBI). The purpose was to determine the overall incidence of ICH progression after chemoprophylaxis in patients with a TBI.

METHODS

This retrospective study was performed at a Level I trauma center, from 1/1/2014 to 12/31/2017. Study patients were drawn from the institution's trauma registry based on Abbreviated Injury Score codes.

RESULTS

778 patients met all inclusion criteria after initial chart review. The proportion of patients with an observed radiographic progression of intracranial hemorrhage after LMWH was 5.8%. 3.1% of patients had a change in clinical management. Observed radiographic progression after LMWH prophylaxis and the presence of SDH on initial CT, the bilateral absence of pupillary response in the emergency department, and a diagnosis of dementia were found to have statistically significant correlation with bleed progression after LMWH was initiated.

CONCLUSION

Over a 4-year period, the use of CT to evaluate for radiographic progression of traumatic intracranial hemorrhage 24 hours after receiving LMWH resulted in a change in clinical management for 3.1% of patients. The odds of intracranial hemorrhage progression were approximately 6.5× greater in patients with subdural hemorrhage on initial CT, 3.1× greater in patients with lack of bilateral pupillary response in ED, and 4.2× greater in patients who had been diagnosed with dementia.

TBI weight-drop model with variable impact heights differentially perturbs hippocampus-cerebellum specific transcriptomic profile

The degree of brain injury is the governing factor for the magnitude of the patient's psycho- and physiological deficits post-injury, and the associated long-term consequences. The present scaling method used to segregate the patients among mild, moderate and severe phases of traumatic brain injury (TBI) has major limitations; however, a more continuous stratification of TBI is still elusive. With the anticipation that differentiating molecular markers could be the backbone of a robust method to triage TBI, we used a modified closed-head injury (CHI) Marmarou model with two impact heights (IH). By definition, IH directly correlates with the impact force causing TBI. In our modified CHI model, the rat skull was fitted with a helmet to permit a diffuse axonal injury. With the frontal cortex as the focal point of injury, the adjacent brain regions (hippocampus, HC and cerebellum, CB) were susceptible to diffuse secondary shock injury. At 8 days post injury (po.i.), rats impacted by 120 cm IH (IH₁₂₀) took a longer time to find an escape route in the Barnes maze as compared to those impacted by 100 cm IH (IH₁₀₀). Using a time-resolved interrogation of the transcriptomic landscape of HC and CB tissues, we mined those genes that altered their regulations in correlation with the variable IHs. At 14 days po.i., when all rats demonstrated nearly normal visuomotor performance, the bio-functional analysis suggested an advanced healing mechanism in the HC of IH₁₀₀ group. In contrast, the HC of IH₁₂₀ group displayed a delayed healing with evidence of active cell death networks. Combining whole genome rat microarrays with behavioral analysis provided the insight of neuroprotective signals that could be the foundation of the next generation triage for TBI patients.

Traumatic Parafalcine Subdural Hematoma: A Clinically Benign Finding

BACKGROUND

Guidelines for management of intracranial hemorrhage do not account for bleed location. We hypothesize that parafalcine subdural hematoma (SDH), as compared to convexity SDH, is a distinct clinical entity and these patients do not benefit from critical care monitoring or repeat imaging.

METHODS

We identified patients presenting to a single level I trauma center with isolated head injuries from February 2016 to August 2017. We identified 88 patients with isolated blunt traumatic parafalcine SDH and 228 with convexity SDH.

RESULTS

Demographics, comorbidities, and use of antiplatelet and anticoagulant agents were similar between the groups. As compared to patients with convexity SDH, patients with parafalcine SDH had a significantly lower incidence of radiographic progression, and had no cases of neurologic deterioration, neurosurgical intervention, or mortality (all P < 0.005). Compared to patients admitted to the intensive care unit, patients with parafalcine SDH admitted to the floor had a shorter length of stay (2.0 ± 1.6 versus 3.8 ± 2.9 d, P < 0.005) with no difference in outcomes.

CONCLUSIONS

Patients presenting with a parafalcine SDH are a distinct and relatively benign clinical entity as compared to convexity SDH and do not benefit from repeat imaging or intensive care unit admission.

Routine repeat head CT may not be necessary for patients with mild TBI

Background

Routine repeat cranial CT (RHCT) is standard of care for CT-verified traumatic brain injury (TBI). Despite mixed evidence, those with mild TBI are subject to radiation and expense from serial CT scans. Thus, we investigated the necessity and utility of RHCT for patients with mild TBI. We hypothesized that repeat head CT in these patients would not alter patient care or outcomes.

Methods

We retrospectively studied patients suffering from mild TBI (Glasgow Coma Scale (GCS) score 13–15) and treated at the R Adams Cowley Shock Trauma Center from November 2014 through January 2015. The primary outcome was the need for surgical intervention. Outcomes were compared using paired Student’s t-test, and stratified by injury on initial CT, GCS change, demographics, and presenting vital signs (mean ± SD).

Results

Eighty-five patients met inclusion criteria with an average initial GCS score=14.6±0.57. Our center sees about 2800 patients with TBI per year, or about 230 per month. This includes patients with concussions. This sample represents about 30% of patients with TBI seen during the study period. Ten patients required operation (four based on initial CT and others for worsening GCS, headaches, large unresolving injury). There was progression of injury on repeat CT scan in only two patients that required operation, and this accompanied clinical deterioration. The mean brain Abbreviated Injury Scale (AIS) score was 4.8±0.3 for surgical patients on initial CT scan compared with 3.4±0.6 (P<0.001) for non-surgical patients. Initial CT subdural hematoma size was 1.1±0.6 cm for surgical patients compared with 0.49±0.3 cm (P=0.05) for non-surgical patients. There was no significant difference between intervention groups in terms of other intracranial injuries, demographics, vital signs, or change in GCS. Overall, 75 patients that did not require surgical intervention received RHCT. At $340 per CT, $51 000 was spent on unnecessary imaging ($367 000/year, extrapolated).

Discussion

In an environment of increased scrutiny on healthcare expenditures, it is necessary to question dogma and eliminate unnecessary cost. Our data questions the use of routine repeat head CT scans in every patient with anatomic TBI and suggests that clinically stable patients with small injury can simply be followed clinically.

Level of evidence

Level III.

Variation in Blood Transfusion and Coagulation Management in Traumatic Brain Injury at the Intensive Care Unit: A Survey in 66 Neurotrauma Centers Participating in the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury Study

Our aim was to describe current approaches and to quantify variability between European intensive care units (ICUs) in patients with traumatic brain injury (TBI). Therefore, we conducted a provider profiling survey as part of the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study. The ICU Questionnaire was sent to 68 centers from 20 countries across Europe and Israel. For this study, we used ICU questions focused on 1) hemoglobin target level (Hb-TL), 2) coagulation management, and 3) deep venous thromboembolism (DVT) prophylaxis. Seventy-eight participants, mostly intensivists and neurosurgeons of 66 centers, completed the ICU questionnaire. For ICU-patients, half of the centers (N = 34; 52%) had a defined Hb-TL in their protocol. For patients with TBI, 26 centers (41%) indicated an Hb-TL between 70 and 90 g/L and 38 centers (59%) above 90 g/L. To treat trauma-related hemostatic abnormalities, the use of fresh frozen plasma (N = 48; 73%) or platelets (N = 34; 52%) was most often reported, followed by the supplementation of vitamin K (N = 26; 39%). Most centers reported using DVT prophylaxis with anticoagulants frequently or always (N = 62; 94%). In the absence of hemorrhagic brain lesions, 14 centers (21%) delayed DVT prophylaxis until 72 h after trauma. If hemorrhagic brain lesions were present, the number of centers delaying DVT prophylaxis for 72 h increased to 29 (46%). Overall, a lack of consensus exists between European ICUs on blood transfusion and coagulation management. The results provide a baseline for the CENTER-TBI study, and the large between-center variation indicates multiple opportunities for comparative effectiveness research.

Venous thromboembolism prophylaxis in neurosurgical trauma patients

BACKGROUND

Venous thromboembolisms (VTEs) occur more frequently in patients with traumatic brain injuries (TBIs) and spinal cord injuries, yet the use of chemoprophylaxis is controversial. The purpose of this study was to investigate the relationship between the timing of chemical VTE prophylaxis initiation and the development of VTE events in these patients.

METHODS

Prospective data were collected and retrospectively reviewed on 1425 patients sustaining TBIs or spinal injuries from 2010 to 2014. Patients were reviewed with respect to age, gender, injury severity score, Glasgow coma score, and mechanism of injury as well as timing of initiation of chemical VTE prophylaxis and presence or absence of VTE.

RESULTS

Patients who developed a VTE had a significantly longer time to initiation of chemical VTE prophylaxis (6.7 ± 4.9 d versus 4.7 ± 4.9 d, P < 0.001) compared with those that did not develop a VTE. Also, for each 1 d increase in time to prophylaxis initiation, the odds of developing a VTE increased significantly (odds ratio = 1.055, P < 0.001). The combination subarachnoid hemorrhage/subdural hemorrhage group was started on VTE prophylaxis significantly later (8.3 ± 6.1 d versus 6.7 ± 3.9 d, P < 0.01) than the overall TBI group and had a higher incidence of VTE (14.4 versus 10.4%, P = NS). In contrast, patients sustaining isolated spinal injuries received chemical VTE prophylaxis significantly earlier (3.4 ± 4.2 d versus 6.7 ± 3.9 d, P < 0.001) and had a significant decrease in their VTE rate (4.4 versus 10.4%, P < 0.0001) compared with the overall TBI group.

CONCLUSIONS

Patients with VTEs had a significant delay in time to initiation of chemoprophylaxis compared with patients without VTEs. Patients sustaining a TBI had a 2-fold delay in initiation of chemoprophylaxis and an associated 2-fold increase in VTE events compared with patients who sustained spinal injuries. Of those patients who developed a TBI, patients who sustained a combination subarachnoid hemorrhage and/or subdural hemorrhage had a significant delay in initiation of chemoprophylaxis with a higher rate of VTE events.

Timing for deep vein thrombosis chemoprophylaxis in traumatic brain injury: an evidence-based review

Multiple studies have addressed deep vein thrombosis chemoprophylaxis timing in traumatic brain injuries. However, a precise time for safe and effective chemoprophylaxis is uncertain according to experts. A comprehensive literature review on brain injuries was performed to delineate temporal proportions for 1) spontaneous intracranial hemorrhage (ICH) progression, 2) post-chemoprophylaxis ICH expansion, and 3) post-chemoprophylaxis deep vein thrombosis. Twenty-three publications were found including more than 5,000 patients. Spontaneous ICH expansion at 24 hours was 14.8% in 1,437 patients from chemoprophylaxis studies and 29.9% in 1,257 patients not in chemoprophylaxis studies (P < 0.0001). With low-risk ICH (n = 136), 99% of spontaneous ICH expansion occurred within 48 hours. In moderate or high-risk ICH (n = 109), 18% of spontaneous ICH expansion occurred after day 3. If patients with pre-chemoprophylaxis ICH expansion are included, the post-chemoprophylaxis ICH expansion proportion was 5.6% in 1,258 patients with chemoprophylaxis on days 1 to 3 and was 1.5% in 401 with chemoprophylaxis after day 3 (P = 0.0116). If patients with pre-chemoprophylaxis ICH expansion were excluded, the post-chemoprophylaxis ICH expansion proportion was 3.1% in 1,570 patients with chemoprophylaxis on days 1 to 3 and was 2.8% in 582 with chemoprophylaxis after day 3 (P = 0.7769). In diffuse axonal injury (n = 188), the post-chemoprophylaxis ICH expansion proportion was 1.6% with chemoprophylaxis after day 3. The deep vein thrombosis proportions were as follows: chemoprophylaxis on days 1 to 3, 2.6% in 2,384 patients; chemoprophylaxis on days 4 or 5, 2.2% in 831; and chemoprophylaxis on day 8, 14.1% in 99 (P < 0.0001). Spontaneous ICH expansion proportions at 24 hours substantially vary between chemoprophylaxis and non-chemoprophylaxis studies. Chemoprophylaxis should not be given within 3 days of injury for moderate-risk or high-risk ICH. Chemoprophylaxis is reasonable when low-risk patients have not developed ICH expansion within 48 hours post-injury. Chemoprophylaxis is also acceptable after day 3, when low-risk patients develop ICH expansion within 48 hours post-injury. In diffuse axonal injury patients who have not developed ICH within 72 hours, chemoprophylaxis is reasonable. Deep vein thrombosis proportions significantly increase when chemoprophylaxis is withheld for greater than 7 days.

The Parkland Protocol's modified Berne-Norwood criteria predict two tiers of risk for traumatic brain injury progression

As a basis for venous thromboembolism (VTE) prophylaxis after traumatic brain injury (TBI), we have previously published an algorithm known as the Parkland Protocol. Patients are classified by risk for spontaneous progression of hemorrhage with chemoprophylaxis regimens tailored to each tier. We sought to validate this schema. In our algorithm, patients with any of the following are classified "low risk" for spontaneous progression: subdural hemorrhage ≤8 mm thick; epidural hemorrhage ≤8 mm thick; contusions ≤20 mm in diameter; a single contusion per lobe; any amount of subarachnoid hemorrhage; or any amount of intraventricular hemorrhage. Patients with any injury exceeding these are "moderate risk" for progression, and any patient receiving a monitor or craniotomy is "high risk." From February 2010 to November 2012, TBI patients were entered into a dedicated database tracking injury types and sizes, risk category at presentation, and progression on subsequent computed tomgraphies (CTs). The cohort (n=414) was classified as low risk (n=200), moderate risk (n=75), or high risk (n=139) after first CT. After repeat CT scan, radiographic progression was noted in 27% of low-risk, 53% of moderate-risk, and 58% of high-risk subjects. Omnibus analysis of variance test for differences in progression rates was highly significant (p<0.0001). Tukey's post-hoc test showed the low-risk progression rate to be significantly different than both the moderate- and high-risk arms; no difference was noted between the moderate- and high-risk arms themselves. These criteria are a valid tool for classifying TBI patients into two categories of risk for spontaneous progression. This supports tailored chemoprophylaxis regimens for each arm.

Does isolated traumatic subarachnoid hemorrhage merit a lower intensity level of observation than other traumatic brain injury?

Evidence is emerging that isolated traumatic subarachnoid hemorrhage (ITSAH) may be a milder form of traumatic brain injury (TBI). If true, ITSAH may not benefit from intensive care unit (ICU) admission, which would, in turn, decrease resource utilization. We conducted a retrospective review of all TBI admissions to our institution between February 2010 and November 2012 to compare the presentation and clinical course of subjects with ITSAH to all other TBI. We then performed descriptive statistics on the subset of ITSAH subjects presenting with a Glasgow Coma Score (GCS) of 13-15. Of 698 subjects, 102 had ITSAH and 596 had any other intracranial hemorrhage pattern. Compared to all other TBI, ITSAH had significantly lower injury severity scores (p<0.0001), lower head abbreviated injury scores (p<0.0001), higher emergency department GCS (p<0.0001), shorter ICU stays (p=0.007), higher discharge GCS (p=0.005), lower mortality (p=0.003), and significantly fewer head computed tomography scans (p<0.0001). Of those ITSAH subjects presenting with a GCS of 13-15 (n=77), none underwent placement of an intracranial monitor or craniotomy. One subject (1.3%) demonstrated a change in exam (worsened headache and dizziness) concomitant with a progression of his intracranial injury. His symptoms resolved with readmission to the ICU and continued observation. Our results suggest that ITSAH are less-severe brain injuries than other TBI. ITSAH patients with GCS scores of 13-15 demonstrate low rates of clinical progression, and when progression occurs, it resolves without further intervention. This subset of TBI patients does not appear to benefit from ICU admission.

Pharmacologic venous thromboembolism prophylaxis after traumatic brain injury: a critical literature review

Despite the frequency and morbidity of venous thromboembolism (VTE) development after traumatic brain injury (TBI), no national standard of care exists to guide TBI caregivers for the use of prophylactic anticoagulation. Fears of iatrogenic propagation of intracranial hemorrhage patterns have led to a dearth of research in this field, and it is only relatively recently that studies dedicated to this question have been performed. These have generally been limited to retrospective and/or observational studies in which patients are classified in a binary fashion as having the presence or absence of intracranial blood. This methodology does not account for the fact that smaller injury patterns stabilize more rapidly, and thus may be able to safely tolerate earlier initiation of prophylactic anticoagulation than larger injury patterns. This review seeks to critically assess the literature on this question by examining the existing evidence on the safety and efficacy of pharmacologic VTE prophylaxis in the setting of elective craniotomy (as this is the closest model available from which to extrapolate) and after TBI. In doing so, we critique studies that approach TBI as a homogenous or a heterogenous study population. Finally, we propose our own theoretical protocol which stratifies patients into low, moderate, and high risk for the likelihood of natural progression of their hemorrhage pattern, and which allows one to tailor a unique VTE prophylaxis regimen to each individual arm.