Alternative dosing of prophylactic enoxaparin in the trauma patient: is more the answer?

Thrombosis prophylaxis following trauma

PURPOSE OF REVIEW

This review explores the persistent occurrence of venous thromboembolic events (VTE) in major trauma patients despite standard thrombosis prophylaxis with low-molecular-weight heparin (LMWH) or unfractionated heparin (UFH). It investigates the inadequacies of standard pharmacologic prophylaxis and proposes alternative approaches not covered in current trauma guidelines.

RECENT FINDINGS

Recent studies highlight the effectiveness of monitoring and adjusting subcutaneous LMWH doses based on anti-Xa levels for the purpose of reducing VTE in trauma patients. The need for dose adaptation arises due to factors like fluctuating organ function, varying antithrombin levels, interaction with plasma proteins, and altered bioavailability influenced by oedema or vasopressor use. Additionally, promising alternatives such as intravenous LMWH, UFH, and argatroban have shown success in intensive care settings.

SUMMARY

The standard dosing of subcutaneous LMWH is often insufficient for effective thrombosis prophylaxis in trauma patients. A more personalised approach, adjusting doses based on specific effect levels like anti-Xa or choosing an alternative mode of anticoagulation, could reduce the risk of insufficient prophylaxis and subsequent VTE.

Multicenter study evaluating target attainment of anti-Factor Xa levels using various enoxaparin prophylactic dosing practices in adult trauma patients

STUDY OBJECTIVE

Enoxaparin is standard of care for venous thromboembolism (VTE) prophylaxis in adult trauma patients, but fixed-dose protocols are suboptimal. Dosing based on body mass index (BMI) or total body weight (TBW) improves target prophylactic anti-Xa level attainment and reduces VTE rates. A novel strategy using estimated blood volume (EBV) may be more effective based on results of a single-center study. This study compared BMI-, TBW-, EBV-based, and hybrid enoxaparin dosing strategies at achieving target prophylactic anti-Factor Xa (anti-Xa) levels in trauma patients.

DESIGN

Multicenter, retrospective review.

DATA SOURCE

Electronic health records from participating institutions.

PATIENTS

Adult trauma patients who received enoxaparin twice daily for VTE prophylaxis and had at least one appropriately timed anti-Xa level (collected 3 to 6 hours after the previous dose after three consecutive doses) from January 2017 through December 2020. Patients were excluded if the hospital-specific dosing protocol was not followed or if they had thermal burns with > 20% body surface area involvement.

INTERVENTION

Dosing strategy used to determine initial prophylactic dose of enoxaparin.

MEASUREMENTS

The primary end point was percentage of patients with peak anti-Xa levels within the target prophylactic range (0.2-0.4 units/mL).

MAIN RESULTS

Nine hospitals enrolled 742 unique patients. The most common dosing strategy was based on BMI (43.0%), followed by EBV (29.0%). Patients dosed using EBV had the highest percentage of target anti-Xa levels (72.1%). Multiple logistic regression demonstrated EBV-based dosing was significantly more likely to yield anti-Xa levels at or above target compared to BMI-based dosing (adjusted odds ratio (aOR) 3.59, 95% confidence interval (CI) 2.29-5.62, p < 0.001). EBV-based dosing was also more likely than hybrid dosing to yield an anti-Xa level at or above target (aOR 2.30, 95% CI 1.33-3.98, p = 0.003). Other pairwise comparisons between dosing strategy groups were nonsignificant.

CONCLUSIONS

An EBV-based dosing strategy was associated with higher odds of achieving anti-Xa level within target range for enoxaparin VTE prophylaxis compared to BMI-based dosing and may be a preferred method for VTE prophylaxis in adult trauma patients.

Monitoring anti-Xa Levels to Optimize Low-Molecular-Weight-Heparin Thromboprophylaxis in High-Risk Hospitalized Patients: A Stratified Meta-Analysis

It is uncertain whether monitoring or targeting anti-Xa levels is necessary when using low-molecular-weight-heparin (LMWH) to prevent venous thromboembolism (VTE). This stratified meta-analysis assessed whether monitoring trough or peak anti-Xa levels with LMWH dosing would reduce risk of VTE. Twelve non-randomized studies involving 3604 hospitalized patients met the inclusion criteria and were subject to meta-analysis. Eight studies assessed the association between VTE and peak anti-Xa levels (between .2 and .5 IU/ml) and four studies assessed the benefits of targeting the trough anti-Xa levels (>.1 IU/ml). Achieving an adequate peak or trough anti-Xa level was associated with a reduced risk of VTE (random-effects model odds ratio [OR] .52, 95% confidence interval [CI] .34-.77; P = .001, I2 = 30% and P-value for heterogeneity = .171) compared with using a fixed standard dose of LMWH. Targeting the trough level (OR .40, 95%CI 0.22-.75, P = .004) appeared to be more effective than targeting the peak level (OR .62, 95%CI 0.37-1.03, P = .066), although a formal interaction analysis did not confirm they were statistically different (ratio of ORs = 1.52, 95%CI 0.68-3.40; z score = 1.03, P = .306). Targeting a higher anti-Xa level did not appear to increase the risk of bleeding or transfusion (OR 1.20, 95%CI 0.46-3.17, P = .707).

Inadequate prophylaxis in patients with trauma: anti-Xa-guided enoxaparin dosing management in critically ill patients with trauma

Venous thromboembolism (VTE) causes significant morbidity in patients with trauma despite advances in pharmacologic therapy. Prior literature suggests standard enoxaparin dosing may not achieve target prophylactic anti-Xa levels. We hypothesize that a new weight-based enoxaparin protocol with anti-Xa monitoring for dose titration in critically injured patients is safe and easily implemented.

Methods

This prospective observational study included patients with trauma admitted to the trauma intensive care unit (ICU) from January 2021 to September 2022. Enoxaparin dosing was adjusted based on anti-Xa levels as standard of care via a performance improvement initiative. The primary outcome was the proportion of subtarget anti-Xa levels (<0.2 IU/mL) on 30 mg two times per day dosing of enoxaparin. Secondary outcomes included the dosing modifications to attain goal anti-Xa levels, VTE and bleeding events, and hospital and ICU lengths of stay.

Results

A total of 282 consecutive patients were included. Baseline demographics revealed a median age of 36 (26-55) years, and 44.7% with penetrating injuries. Of these, 119 (42.7%) achieved a target anti-Xa level on a starting dose of 30 mg two times per day. Dose modifications for subtarget anti-Xa levels were required in 163 patients (57.8%). Of those, 120 underwent at least one dose modification, which resulted in 78 patients (47.8%) who achieved a target level prior to hospital discharge on a higher dose of enoxaparin. Overall, only 69.1% of patients achieved goal anti-Xa level prior to hospital discharge. VTE occurred in 25 patients (8.8%) and major bleeding in 3 (1.1%) patients.

Conclusion

A majority of critically injured patients do not meet target anti-Xa levels with 30 mg two times per day enoxaparin dosing. This study highlights the need for anti-Xa-based dose modification and efficacy of a pharmacy-driven protocol. Further optimization is warranted to mitigate VTE events.

Level of evidence

Therapeutic/care management, level III.

Early administration of high dose enoxaparin after traumatic brain injury

BACKGROUND

Early enoxaparin 30 mg BID administration at 24 h post-injury has been demonstrated in patients with traumatic brain injury (TBI). However this dose can also yield subtherapeutic anti-Xa levels in 30-50% of trauma patients, suggesting that larger doses may be required for adequate prophylaxis against venous thromboembolism (VTE). The safety of enoxaparin 40 mg BID in trauma patients has previously been shown - however, these studies have largely excluded TBI patients. Therefore, we sought to demonstrate the safety of early enoxaparin 40 mg BID in a low-risk group of TBI patients.

METHODS

A retrospective review of TBI patients at a Level 1 trauma center was performed. Patients with stable computed tomography (CT) of the head at 6 to 24 h post-injury who received enoxaparin 40 mg BID were included and serial GCS evaluations to identify possible clinical complications. To evaluate the safety of this dosing regimen, data was then compared to patients from our institution with similar TBI profiles who had received 5,000 units (U) of subcutaneous heparin (SQH) prophylaxis.

RESULTS

199 TBI patients were identified over a nine month period, 40/199 (19.7%) received DVT prophylaxis after traumatic injury. Of these 40, 19 (47.5%) received enoxaparin 40 mg BID and 21 (52.5%) received 5,000U of SQH. Low risk TBI patients who were either given enoxaparin (n = 7) or SQH (n = 4), demonstrated no clinical decline in mental status during their inpatient stay.

CONCLUSION

Prior studies have demonstrated that enoxaparin 40 mg BID dosing is superior to traditional VTE prophylaxis in trauma patients. However, TBI patients are often excluded from this dosing due to concern for progression. Our study showed no clinical decline in mental status in a small cohort of low-risk TBI patients who received enoxaparin 40 mg BID.

The efficacy of various Enoxaparin dosing regimens in general surgery patients: A systematic review

BACKGROUND

Patients undergoing surgical procedures are at an increased risk of venous thromboembolism events. A fixed Enoxaparin dosing regimen is the standard of care for chemoprophylaxis in most institutions; however, breakthrough venous thromboembolism events are still reported. We aimed to systematically review the literature to determine the ability of various Enoxaparin dosing regimens to achieve adequate prophylactic anti-Xa levels for venous thromboembolism prevention in hospitalized general surgery patients. Additionally, we aimed to assess the correlation between subprophylactic anti-Xa levels and the development of clinically significant venous thromboembolism events.

METHODS

A systematic review was conducted using major databases from January 1, 1993, to February 17, 2023. Two independent researchers screened titles and abstracts, followed by a full-text review. Articles were included if Enoxaparin dosing regimens were evaluated by anti-Xa levels. Exclusion criteria included systematic reviews, pediatric population, nongeneral surgery (defined as trauma, orthopedics, plastics, and neurosurgery), and non-Enoxaparin chemoprophylaxis. The primary outcome was peak Anti-Xa level measured at steady state concentration. The risk of bias was assessed using the Risk of Bias in Nonrandomized studies-of Intervention tool.

RESULTS

A total of 6,760 articles were extracted, of which 19 were included in the scoping review. Nine studies included bariatric patients, whereas 5 studies explored abdominal surgical oncology patients. Three studies assessed thoracic surgery patients, and 2 studies included patients undergoing "general surgery" procedures. A total of 1,502 patients were included. The mean age was 47 years, and 38% were males. The percentages of patients reaching adequate prophylactic anti-Xa levels were 39%, 61%, 15%, 50%, and 78% across the 40 mg daily, 40 mg twice daily, 30 mg twice daily, and weight-tiered, and body mass index-based groups, respectively. The overall risk of bias was low to moderate.

CONCLUSION

Fixed Enoxaparin dosing regimens are not correlated with adequate anti-Xa levels in general surgery patients. Additional research is warranted to assess the efficacy of dosing regimens based on novel physiologic parameters (such as estimated blood volume).

Effectiveness and Safety of High-Dose Thromboprophylaxis in Morbidly Obese Major Trauma Patients

BACKGROUND

Trauma increases risk for venous thromboembolism (VTE) and obesity is a known independent risk factor for VTE development. Currently, no consensus on an optimal prophylactic dosing strategy for morbidly obese trauma patients exists. The objective of this study is to evaluate the effectiveness and safety of a BMI-stratified dosing strategy for VTE prophylaxis in morbidly obese trauma patients.

METHODS

This was a single center, retrospective cohort study of adult major trauma patients with a body mass index (BMI) of ≥40 kg/m2 admitted to the surgical-trauma intensive care unit from April 2014 to July 2020. Patients included were those who received enoxaparin 40 mg subcutaneously (SQ) every 12 hours (Q12H) for BMI of 40 to 49.9 kg/m2 or 60 mg SQ Q12H BMI ≥ 50 kg/m2 (per protocol), or enoxaparin 40 mg SQ Q12H for BMI of 40 to 49.9 kg/m2 (non-protocol). The primary endpoint was confirmed incidence of VTE. Secondary endpoints included occurrence of deep vein thrombosis (DVT) or pulmonary embolism (PE) during hospitalization, bleeding events, intensive care unit (ICU) and hospital length of stay (LOS) and hospital mortality.

RESULTS

One hundred forty-five morbidly obese major trauma patients were included, with 123 patients (84.8%) in the per-protocol group. The primary outcome of in-hospital VTE did not occur in any patients in this group. Bleeding events occurred in 3 patients (2.7%) with a BMI of 40 to 49.9 kg/m2 and in 2 patients (16.7%) with a BMI of ≥50 kg/m2 (P = .064). Twenty-two patients in the non-protocol group were reviewed. One VTE event (4.5%) and no bleeding events occurred in this group. Median ICU LOS was 5 days, and hospital LOS was 11 days for the entire study group.

CONCLUSIONS

Administration of enoxaparin 40 mg SQ Q12H to morbidly obese major trauma patients with a BMI of 40 to 49.9 kg/m2 and enoxaparin 60 mg SQ Q12H in those with a BMI of ≥50 kg/m2 resulted in low rates of VTE and bleeding events in the current study. However, future larger studies using this BMI-stratified dosing strategy are necessary to confirm these findings.

Survey of venous thromboembolism prophylaxis in trauma patients: current prescribing practices and concordance with clinical practice guidelines

Objectives

Pharmacological venous thromboembolism (VTE) prophylaxis is recommended in the vast majority of trauma patients. The purpose of this study was to characterize current dosing practices and timing of initiation of pharmacological VTE chemoprophylaxis at trauma centers.

Methods

This was an international, cross-sectional survey of trauma providers. The survey was sponsored by the American Association for the Surgery of Trauma (AAST) and distributed to AAST members. The survey included 38 questions about practitioner demographics, experience, level and location of trauma center, and individual/site-specific practices regarding the dosing, selection, and timing of initiation of pharmacological VTE chemoprophylaxis in trauma patients.

Results

One hundred eighteen trauma providers responded (estimated response rate 6.9%). Most respondents were at level 1 trauma centers (100/118; 84.7%) and had >10 years of experience (73/118; 61.9%). While multiple dosing regimens were used, the most common dose reported was enoxaparin 30 mg every 12 hours (80/118; 67.8%). The majority of respondents (88/118; 74.6%) indicated adjusting the dose in patients with obesity. Seventy-eight (66.1%) routinely use antifactor Xa levels to guide dosing. Respondents at academic institutions were more likely to use guideline-directed dosing (based on the Eastern Association of the Surgery of Trauma and the Western Trauma Association guidelines) of VTE chemoprophylaxis compared with those at non-academic centers (86.2% vs 62.5%; p=0.0158) and guideline-directed dosing was reported more often if the trauma team included a clinical pharmacist (88.2% vs 69.0%; p=0.0142). Wide variability in initial timing of VTE chemoprophylaxis after traumatic brain injury, solid organ injury, and spinal cord injuries was found.

Conclusions

A high degree of variability exists in prescribing and monitoring practices for the prevention of VTE in trauma patients. Clinical pharmacists may be helpful on trauma teams to optimize dosing and increase prescribing of guideline-concordant VTE chemoprophylaxis.

Low Anti-Factor Xa Level Predicts 90-Day Symptomatic Venous Thromboembolism in Surgical Patients Receiving Enoxaparin Prophylaxis: A Pooled Analysis of Eight Clinical Trials

OBJECTIVE

To examine the relationship between enoxaparin dose adequacy, quantified with anti-Factor Xa (aFXa) levels, and 90-day symptomatic venous thromboembolism (VTE) and postoperative bleeding.

SUMMARY BACKGROUND DATA

Surgical patients often develop "breakthrough" VTE events-those which occur despite receiving chemical anticoagulation. We hypothesize that surgical patients with low aFXa levels will be more likely to develop 90-day VTE, and those with high aFXa will be more likely to bleed.

METHODS

Pooled analysis of eight clinical trials (N = 985) from a single institution over a 4 year period. Patients had peak steady state aFXa levels in response to a known initial enoxaparin dose, and were followed for 90 days. Survival analysis log-rank test examined associations between aFXa level category and 90-day symptomatic VTE and bleeding.

RESULTS

Among 985 patients, 2.3% (n = 23) had symptomatic 90-day VTE, 4.2% (n = 41) had 90-day clinically relevant bleeding, and 2.1% (n = 21) had major bleeding. Patients with initial low aFXa were significantly more likely to have 90-day VTE than patients with adequate or high aFXa (4.2% vs 1.3%, P = 0.007). In a stratified analysis, this relationship was significant for patients who received twice daily (6.2% vs 1.5%, P = 0.003), but not once daily (3.0% vs 0.7%, P = 0.10) enoxaparin. No association was seen between high aFXa and 90-day clinically relevant bleeding (4.8% vs 2.9%, P = 0.34) or major bleeding (3.6% vs 1.6%, P = 0.18).

CONCLUSIONS

This manuscript establishes inadequate enoxaparin dosing as a plausible mechanism for breakthrough VTE in surgical patients, and identifies anticoagulant dose adequacy as a novel target for process improvement measures.

Design and Retrospective Application of a Spine Trauma DVT Prophylaxis Protocol on Level 1 Trauma Center Patient Database

STUDY DESIGN

Systematic literature review.

OBJECTIVES

The impact of thromboembolic disease on the morbidity and mortality of patients with acute spinal cord injury is well documented, with rates as high as 67%-100% among untreated patients. The efficacy of mechanical prophylaxis as a stand-alone measure has been questioned, so we sought to determine a safe perioperative window for chemical anticoagulation use after spine surgery. Many surgeons have concerns anticoagulants may cause post-operative hematoma.

METHODS

A systematic literature review was performed, ultimately yielding 13 articles. Based on the existing literature and input from our multidisciplinary institutional trauma committee, a Spine Trauma DVT Prophylaxis Protocol was developed.

RESULTS

Effort was placed to identify cases within our institution in which patients suffered vertebral column fractures and/or spinal cord injuries. Of these 466 vertebral column fractures and/or spinal cord injuries, 4 patients were identified and diagnosed with DVTs while admitted.

CONCLUSIONS

Of these patients, there is a clear dilemma with regard to safety of chemoprophylaxis use versus risk of developing a DVT. Though none of the patients developed a PE, utilizing the protocol would have led to earlier IVC filter placement or initiation of a VTE surveillance protocol in 2 of the patients. Initiation of enoxaparin before surgery in one patient (despite delay of surgical timing) may have avoided his subsequent LUE DVT. Though not appropriate for all clinical scenarios, we are confident that our treatment algorithm will prove beneficial for patient care in avoiding DVTs and helping trauma surgeons with evidence-based clinical decision making.

Enoxaparin titrated by anti-Xa levels reduces venous thromboembolism in trauma patients

BACKGROUND

Trauma is a major risk factor for the development of a venous thromboembolism (VTE). After observing higher than expected VTE rates within our center's Trauma Quality Improvement Program data, we instituted a change in our VTE prophylaxis protocol, moving to enoxaparin dosing titrated by anti-Xa levels. We hypothesized that this intervention would lower our symptomatic VTE rates.

METHODS

Adult trauma patients at a single institution meeting National Trauma Data Standard criteria from April 2015 to September 2019 were examined with regards to VTE chemoprophylaxis regimen and VTE incidence. Two groups of patients were identified based on VTE protocol-those who received enoxaparin 30 mg twice daily without routine anti-Xa levels ("pre") versus those who received enoxaparin 40 mg twice daily with dose titrated by serial anti-Xa levels ("post"). Univariate and multivariate analyses were performed to define statistically significant differences in VTE incidence between the two cohorts.

RESULTS

There were 1698 patients within the "pre" group and 1406 patients within the "post" group. The two groups were essentially the same in terms of demographics and risk factors for bleeding or thrombosis. There was a statistically significant reduction in VTE rate (p = 0.01) and deep vein thrombosis rate (p = 0.01) but no significant reduction in pulmonary embolism rate (p = 0.21) after implementation of the anti-Xa titration protocol. Risk-adjusted Trauma Quality Improvement Program data showed an improvement in rate of symptomatic pulmonary embolism from fifth decile to first decile.

CONCLUSION

A protocol titrating prophylactic enoxaparin dose based on anti-Xa levels reduced VTE rates. Implementation of this type of protocol requires diligence from the physician and pharmacist team. Further research will investigate the impact of protocol compliance and time to appropriate anti-Xa level on incidence of VTE.

LEVEL OF EVIDENCE

Therapeutic/care management, Level IV.

Supraprophylactic Anti-Factor Xa Levels Are Associated with Major Bleeding in Neurosurgery Patients Receiving Prophylactic Enoxaparin

BACKGROUND

Prior studies demonstrated reduced risk for venous thromboembolism (VTE) in neurosurgical patients secondary to prophylaxis with both heparin and low-molecular-weight heparin. The ability to monitor low-molecular-weight heparin by obtaining anti-factor Xa (anti-Xa) serum levels provides an opportunity to evaluate safety and efficacy. The aim of this study was to describe characteristics of patients who have anti-Xa levels outside of the goal range (0.2-0.4/0.5 IU/mL) and investigate incidence of major bleeding and VTE.

METHODS

A single-center, retrospective, observational study was conducted on neurosurgical patients receiving enoxaparin for VTE prophylaxis between August 2019 and December 2020. Significance testing was conducted via Fisher exact test and independent samples t test.

RESULTS

The study included 85 patients. Patients were less likely to have an anti-Xa level in the goal range if they were male, had a higher weight, or were morbidly obese. Three neuroendovascular patients (3.5%) experienced a major bleed. Serum anti-Xa levels were significantly higher in patients who experienced major bleeds compared with patients who did not (0.45 ± 0.16 IU/mL vs. 0.28 ± 0.09 IU/mL, P = 0.003). Patients with a supraprophylactic anti-Xa level (>0.5 IU/mL) were more likely to experience a major bleed (P = 0.005). One VTE event occurred: the patient experienced a pulmonary embolism with anti-Xa level at goal.

CONCLUSIONS

Anti-Xa-guided enoxaparin dosing for VTE prophylaxis in neurosurgical patients may help prevent major bleeding. These data suggest that a higher anti-Xa level may predispose patients to major bleeding. Further evaluation is needed to identify the goal anti-Xa level for VTE prophylaxis in this population.

Optimal Dosing of Prophylactic Enoxaparin after Surgical Procedures: Results of the Double-Blind, Randomized, Controlled FIxed or Variable Enoxaparin (FIVE) Trial

BACKGROUND

The accepted "one-size-fits-all" dose strategy for prophylactic enoxaparin may not optimize the medication's risks and benefits after surgical procedures. The authors hypothesized that weight-based administration might improve the pharmacokinetics of prophylactic enoxaparin when compared to fixed-dose administration.

METHODS

The FIxed or Variable Enoxaparin (FIVE) trial was a randomized, double-blind trial that compared the pharmacokinetic and clinical outcomes of patients assigned randomly to postoperative venous thromboembolism prophylaxis using enoxaparin 40 mg twice daily or enoxaparin 0.5 mg/kg twice daily. Patients were randomized after surgery and received the first enoxaparin dose at 8 hours after surgery. Primary hypotheses were (1) weight-based administration is noninferior to a fixed dose for avoiding underanticoagulation (anti-factor Xa <0.2 IU/ml) and (2) weight-based administration is superior to fixed-dose administration for avoiding overanticoagulation (anti-factor Xa >0.4 IU/ml). Secondary endpoints were 90-day venous thromboembolism and bleeding.

RESULTS

In total, 295 patients were randomized, with 151 assigned to fixed-dose and 144 to weight-based administration of enoxaparin. For avoidance of under anticoagulation, weight-based administration had a greater effectiveness (79.9 percent versus 76.6 percent); the 3.3 percent (95 percent CI, -7.5 to 12.5 percent) greater effectiveness achieved statistically significant noninferiority relative to the a priori specified -12 percent noninferiority margin (p = 0.004). For avoidance of overanticoagulation, weight-based enoxaparin administration was superior to fixed-dose administration (90.6 percent versus 82.2 percent); the 8.4 percent (95 percent CI, 0.1 to 16.6 percent) greater effectiveness showed significant safety superiority (p = 0.046). Ninety-day venous thromboembolism and major bleeding were not different between fixed-dose and weight-based cohorts (0.66 percent versus 0.69 percent, p = 0.98; 3.3 percent versus 4.2 percent, p = 0.72, respectively).

CONCLUSION

Weight-based administration showed superior pharmacokinetics for avoidance of underanticoagulation and overanticoagulation in postoperative patients receiving prophylactic enoxaparin.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, I.

Venous Thromboembolism Chemoprophylaxis in Trauma and Emergency General Surgery Patients: A Systematic Review

BACKGROUND

Appropriate venous thromboembolism (VTE) chemoprophylaxis in trauma and emergency general surgery (EGS) patients is crucial.

OBJECTIVE

The purpose of this study is to review the recent literature and offer recommendations for VTE chemoprophylaxis in trauma and EGS patients.

METHODS

We conducted a literature search from 2000 to 2021 for articles investigating VTE chemoprophylaxis in adult trauma and EGS patients. This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines.

RESULTS

Our search resulted in 34 articles. Most studies showed low-molecular-weight heparin (LMWH) is similar to unfractionated heparin (UFH) for VTE prevention; however, LMWH was more commonly used. Adjusted chemoprophylaxis dosing did not change the VTE rate but the timing did. Direct oral anticoagulants (DOACs) have been shown to be safe and effective in trauma and traumatic brain injury (TBI)/spinal cord injury (SCI). Studies showed VTE prophylaxis in EGS can be inconsistent and improves with guidelines that lower VTE events.

CONCLUSIONS

There may be no benefit to receiving LMWH over UFH in trauma patients. In addition, different drugs under the class of LMWH do not change the incidence of VTE. Adjusted dosing of enoxaparin does not seem to affect VTE incidence. The use of DOACs in the trauma TBI and SCI setting has been shown to be safe and effective in reducing VTE. One important consideration with VTE prophylaxis may be the timing of prophylaxis initiation, specifically as it relates to TBI, with a higher likelihood of developing VTE as time progresses. EGS patients are at a high risk of VTE. Improved compliance with clinical guidelines in this population is correlated with decreased thrombotic events.

What Do We Know about Thromboprophylaxis and Its Monitoring in Critically Ill Patients?

Venous thromboembolism (VTE), including deep vein thrombosis and pulmonary embolism, is an important complication in patients hospitalized in intensive care units (ICU). Thromboprophylaxis is mainly performed with Low Molecular Weight Heparin (LMWH) and, in some specific patients, with Unfractionated Heparin (UFH). These intensive units are an environment where individual patient variability is extreme and where traditional antithrombotic protocols are frequently ineffective. This was known for a long time, but the hospitalization of many patients with COVID-19 inflammatory storms suddenly highlighted this knowledge. It is therefore reasonable to propose variable antithrombotic prevention protocols based initially on a series of individual criteria (weight, BMI, and thrombotic risks). Secondly, they should be adjusted by the monitoring of anticoagulant activity, preferably by measuring the anti-Xa activity. However, we still face unresolved questions, such as once- or twice-daily LMWH injections, monitoring at the peak and/or trough, and poorly defined therapeutic targets. Equally surprisingly, we observed a lack of standardization of the anti-Xa activity kits.

Pharmacokinetics of enoxaparin in COVID-19 critically ill patients

Background

In intensive-care unit (ICU) patients, pathophysiological changes may affect the pharmacokinetics of enoxaparin and result in underdosing.

Objectives

To develop a pharmacokinetic model of enoxaparin to predict the time-exposure profiles of various thromboprophylactic regimens in COVID-19 ICU-patients.

Methods

This was a retrospective study in ICUs of two French hospitals. Anti-Xa activities from consecutive patients with laboratory-confirmed SARS-CoV-2 infection treated with enoxaparin for the prevention or the treatment of venous thrombosis were used to develop a population pharmacokinetic model using non-linear mixed effects techniques. Monte Carlo simulations were then performed to predict enoxaparin exposure at steady-state after three days of administration.

Results

A total of 391 anti-Xa samples were measured in 95 patients. A one-compartment model with first-order kinetics best fitted the data. The covariate analysis showed that enoxaparin clearance (typical value 1.1 L.h-1) was related to renal function estimated by the CKD-EPI formula and volume of distribution (typical value 17.9 L) to actual body weight.

Simulation of anti-Xa activities with enoxaparin 40 mg qd indicated that 64% of the patients had peak levels within the range 0.2 to 0.5 IU.mL-1 and 75% had 12-hour levels above 0.1 IU.mL-1. Administration of a total daily dose of at least 60 mg per day improved the probability of target attainment.

Conclusion

In ICU COVID-19 patients, exposure to enoxaparin is reduced due to an increase in the volume of distribution and clearance. Consequently, enoxaparin 40 mg qd is suboptimal to attain thromboprophylactic anti-Xa levels.

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.

Achievement of goal anti-Xa activity with weight-based enoxaparin dosing for venous thromboembolism prophylaxis in trauma patients

STUDY OBJECTIVE

The purpose of this study was to evaluate the utility of routine anti-Xa peak monitoring for trauma patients initiated on weight-based enoxaparin for venous thromboembolism (VTE) prophylaxis and identify patient populations where monitoring is necessary.

DESIGN

Retrospective study.

SETTING

Augusta University (AU) Medical Center in Augusta, Georgia, a level 1 trauma center.

PATIENTS

Adult patients admitted to the trauma surgery service requiring chemical VTE prophylaxis.

INTERVENTION

At least three consecutive doses of enoxaparin 0.5 mg/kg subcutaneously every 12 hour for VTE prophylaxis prior to an anti-Xa peak as the initial chemical VTE prophylaxis strategy.

MEASUREMENTS

The primary end point was the percentage of patients who achieved goal anti-Xa peak of 0.2-0.6 unit/ml. The incidence of newly diagnosed VTE and clinically significant bleeding were assessed as secondary end points.

MAIN RESULTS

From January 1, 2018, through February 28, 2019, 300 patients met inclusion criteria. Anti-Xa peaks were within goal in 91% of all patients, 7.7% were below goal, and 1.3% were above goal. For patients who did not meet the goal, dose adjustments were made in 70.4% of patients. New levels were obtained in 73.7% of those patients, and all repeat levels was within goal. Clinically significant bleeding occurred in 5.3% of patients. Newly diagnosed VTE occurred in 1.7% of patients.

CONCLUSIONS

The use of initial weight-based enoxaparin dosing in trauma patients routinely achieved the prespecified target anti-Xa goal. In conclusion, anti-Xa levels are not necessary for routine monitoring of weight-based enoxaparin for VTE prophylaxis in trauma patients. Incidence of clinically significant bleeding and newly diagnosed VTE were similar to previous studies.

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.

Single-center Experience with Venous Thromboembolism Prophylaxis for Obese Burn Patients

Burn injured patients are at high risk of thromboembolic complications. Morbid obesity further increases this risk. Our objective was to evaluate the efficacy of enoxaparin dosed 40 mg twice daily in achieving prophylactic plasma anti-Xa levels in obese burn patients. A retrospective chart review from November 2018 until September 2019 identified patients who were either ≥100 kg or had a body mass index ≥30 kg/m2 and initiated on enoxaparin 40 mg twice daily for venous thromboembolism prophylaxis. Patients were ≥18 yr of age and received ≥3 sequential doses of enoxaparin with appropriately timed peak plasma anti-Xa levels to monitor efficacy. One hundred forty-eight patients were screened with 43 patients included for analysis. Forty-two percent of the patients did not reach target peak plasma anti-Xa levels (0.2-0.5 IU/ml) on enoxaparin 40 mg twice daily. Patients who did not meet prophylactic target levels were more likely to be male (P < 0.05) and have an increased mean body weight (129 ± 24 kg vs 110 ± 16 kg, P < 0.05). Thirteen out of 18 patients received dosage adjustments with subsequent anti-Xa levels available for follow-up assessment, of which an additional six patients required further dosage adjustment to meet prophylactic goals. Current utilization of a fixed 40 mg twice daily regimen of enoxaparin for venous thromboembolism (VTE) is inadequate to meet target prophylactic peak plasma anti-Xa levels in the obese burn patient population. Dose adjusting enoxaparin to target anti-Xa levels to reduce VTE rates in obese burn patients should be further evaluated.

Risk factors for postdischarge venous thromboembolism among bariatric surgery patients and the evolving approach to extended thromboprophylaxis with enoxaparin

BACKGROUND

Venous thromboembolism (VTE) is one of the most common causes of postoperative mortality following bariatric surgery. The majority of VTE events occur after discharge from the hospital. Little consensus exists regarding who should receive extended enoxaparin thromboprophylaxis or how they should be dosed, namely whether to use weight-based or BMI-stratified dosing strategies.

OBJECTIVES

Provide an overview of the risk factors associated with VTE in procedures among bariatric patients including the use of predictive tools to stratify risk and the various approaches to enoxaparin chemoprophylaxis in obesity.

SETTING

Multiple centers.

METHODS

A review of the literature identified studies evaluating risk factors for VTE including demographic characteristics, co-morbidities, and operative factors. The use of calculators to stratify patients by risk and approaches to extended thromboprophylaxis in obesity were evaluated as well.

RESULTS

VTE was associated with increased age, weight, male sex, and prior history of VTE, all frequently included in risk calculators. Outside of those major risk factors, there is little consensus about the importance of patient diagnoses. Weight-based dosing was often superior to standardized dosing in studies across disciplines in generating target anti-Xa levels however there is no consistent association of reduced risk of VTE with therapeutic anti-Xa levels.

CONCLUSIONS

Risk calculators may be a valuable tool for identifying patients at high-risk for VTE, but their efficacy depends on the rating algorithm and inclusion of various risk factors and is methodologically limited by prophylactic interventions. Future work should consider if biochemical factors should be included in patient stratification approaches in particular when defining the ideal chemoprophylaxis approach. Transparency and consistency in data collection and reporting is needed to better assess and inform the ideal dosing strategy to prevent VTE following bariatric surgery.

Weight-Based Enoxaparin Achieves Adequate Anti-Xa Levels More Often in Trauma Patients: A Prospective Study

BACKGROUND

Previous research demonstrates that twice-daily enoxaparin is inadequate for venous thromboembolic (VTE) prophylaxis in critically ill trauma patients prompting dose adjustment based on anti-Xa levels. Most studies evaluate peak anti-Xa levels; however, data suggest that trough levels are associated with decreased VTE. We evaluated trough anti-Xa levels in noncritically ill trauma patients receiving fixed or weight-based enoxaparin.

METHODS

Peak and trough anti-Xa levels were prospectively collected from patients receiving at least 3 consecutive doses of enoxaparin (PRE). A performance improvement project prompted a change to weight-based dosing. Peak and trough levels were subsequently prospectively collected from the weight-based group (POST). Adequate peak was defined as ≥0.2 IU/mL and adequate trough as ≥0.1 IU/mL. PRE and POST groups were compared.

RESULTS

200 patients were evaluated (100 PRE, 100 POST). In the PRE group, only 34% of trough and 61% of peak anti-Xa levels were adequate compared with 82% and 97%, respectively, in the POST group (P < .01). Median trough improved from 0.07 IU/mL to 0.2 IU/mL (P < .01). Median peak improved from 0.22 IU/mL to 0.47 IU/mL (P < .01). More patients achieved adequate peak and trough levels in the POST group (79% vs 31%, P < .01). 95% of patients with adequate troughs also had adequate peaks, whereas 75% with adequate peaks had adequate troughs.

DISCUSSION

Traditional enoxaparin dosing in noncritically ill trauma patients results in suboptimal anti-Xa levels. Weight-based enoxaparin improves both trough and peak anti-Xa levels obviating dose adjustment. Furthermore, troughs better predict adequate anti-Xa levels.

Assessment of Anti-Factor Xa Levels of Patients Undergoing Colorectal Surgery Given Once-Daily Enoxaparin Prophylaxis: A Clinical Study Examining Enoxaparin Pharmacokinetics

Importance

Between 4% and 12% of patients undergoing colorectal surgery and receiving enoxaparin, 40 mg per day, have a postoperative venous thromboembolism (VTE) event. An improved understanding of why "breakthrough" VTE events occur despite guideline-compliant prophylaxis is an important patient safety question.

Objective

To determine the proportion of patients undergoing colorectal surgery who received adequate anticoagulation based on peak anti-factor Xa (aFXa) levels while receiving enoxaparin at 40 mg per day.

Design, Setting, and Participants

This prospective, nonrandomized clinical trial was conducted between February 2017 and July 2018 with 90-day follow-up at a quaternary academic medical center in the Intermountain West and included patients undergoing colorectal surgery who had surgery after receiving general anesthesia, were admitted for at least 3 days, and received enoxaparin, 40 mg once daily.

Interventions

All patients had aFXa levels measured after receiving enoxaparin 40 mg per day. Patients whose aFXa level was out of range entered the trial's interventional arm where real-time enoxaparin dose adjustment and repeated aFXa measurement were performed.

Main Outcomes and Measures

Primary outcome: in-range peak aFXa levels (goal range, 0.3-0.5 IU/mL) with enoxaparin, 40 mg per day. Secondary outcomes: (1) in-range trough aFXa levels (goal range, 0.1-0.2 IU/mL) and (2) the proportion of patients with in-range peak aFXa levels from enoxaparin, 40 mg once daily, vs the real-time enoxaparin dose adjustment protocol.

Results

Over 16 months, 116 patients undergoing colorectal surgery (65 women [56.0%]; 99 white individuals [85.3%], 13 Hispanic or Latino individuals [11.2%], and 4 Pacific Islander individuals [3.5%]; mean [range] age, 52.1 [18-85] years) were enrolled. Among 106 patients (91.4%) whose peak aFXa level was appropriately drawn, 72 (67.9%) received inadequate anticoagulation (aFXa < 0.3 IU/mL) with enoxaparin, 40 mg per day. Weight and peak aFXa levels were inversely correlated (r2 = 0.38). Forty-seven patients (77%) had a trough aFXa level that was not detectable (ie, most patients had no detectable level of anticoagulation for at least 12 hours per day). Real-time enoxaparin dose adjustment was effective. Patients were significantly more likely to achieve an in-range peak aFXa with real-time dose adjustment as opposed to fixed dosing alone (85.4% vs 29.2%, P < .001).

Conclusions and Relevance

This study supports the finding that most patients undergoing colorectal surgery receive inadequate prophylaxis from enoxaparin, 40 mg once daily. These findings may explain the high rate of "breakthrough" VTE observed in many clinical trials.

Trial Registration

ClinicalTrials.gov identifier: NCT02704052.

Rethinking the one-size-fits-most approach to venous thromboembolism prophylaxis after radical cystectomy

OBJECTIVES

Empirically dosed enoxaparin is routinely given in the postoperative period for venous thromboembolism (VTE) prophylaxis after radical cystectomy (RC). Patient-specific factors may alter its pharmacokinetics, and it is unclear whether this leads to levels sufficient for antithrombosis. We sought to evaluate variability of anti-factor Xa levels in a cohort of RC patients receiving perioperative enoxaparin prophylaxis.

MATERIAL AND METHODS

Patients undergoing RC at a single institution were placed on a postoperative pathway that included enoxaparin. An anti-factor Xa level was drawn 2 to 4 hours after the third dose. The target range for prophylaxis was 0.3 IU/ml to 0.5 IU/ml.

RESULTS

The primary outcome was anti-factor Xa level. Demographics, operative time, hospital course, and 30-days post-operative VTE were compared by anti-factor Xa level group using univariate and multivariable analyses. Between January 2018 and 2019, 107 RC patients remained on pathway and were included in our analysis. Sixty-five (61%) were below target range for VTE prophylaxis.  A single VTE event (0.9%) occurred in a subprophylactic individual. The subprophylactic group had a significantly higher body mass index (P < 0.01) than those within target range.

CONCLUSIONS

Higher body mass index was associated with subprophylactic enoxaparin dosing after RC. Nearly two-thirds of patients had below target anti-factor Xa levels. This suggests that dosing could be further individualized, but given the low incidence of VTE, implications of dose-adjusted prophylaxis on VTE prevention remain unknown.

Call to Action to Prevent Venous Thromboembolism in Hospitalized Patients: A Policy Statement From the American Heart Association

Venous thromboembolism (VTE) is a major preventable disease that affects hospitalized inpatients. Risk stratification and prophylactic measures have good evidence supporting their use, but multiple reasons exist that prevent full adoption, compliance, and efficacy that may underlie the persistence of VTE over the past several decades. This policy statement provides a focused review of VTE, risk scoring systems, prophylaxis, and tracking methods. From this summary, 5 major areas of policy guidance are presented that the American Heart Association believes will lead to better implementation, tracking, and prevention of VTE events. They include performing VTE risk assessment and reporting the level of VTE risk in all hospitalized patients, integrating preventable VTE as a benchmark for hospital comparison and pay-for-performance programs, supporting appropriations to improve public awareness of VTE, tracking VTE nationwide with the use of standardized definitions, and developing a centralized data steward for data tracking on VTE risk assessment, prophylaxis, and rates.

Fixed or Weight-Tiered Enoxaparin After Thoracic Surgery for Venous Thromboembolism Prevention

BACKGROUND

Venous thromboembolism is an important patient safety issue in thoracic surgery patients. The optimal enoxaparin dose remains unclear. This multicenter pre/post clinical trial compared the pharmacokinetics of fixed versus weight-tiered enoxaparin, and their impact on 90-day venous thromboembolism and bleeding.

METHODS

Thoracic surgery patients were prospectively enrolled using a pre/post study design. Cohort 1 received enoxaparin 40 mg daily, and cohort 2 received a weight-tiered regimen: less than 70 kg received 30 mg daily; 70 kg to 89.9 kg received 40 mg once daily; and 90 kg or more received 50 mg daily. The primary study outcome was peak anti-factor Xa levels in response to fixed or weight-tiered enoxaparin. Secondary outcomes included trough anti-factor Xa, 90-day symptomatic venous thromboembolism, and 90-day clinically relevant bleeding.

RESULTS

One hundred thirty-one patients were prospectively enrolled, including 65 in the fixed-dose cohort and 66 in the weight-tiered cohort. No patient was lost to follow-up. Weight-tiered enoxaparin was not significantly more likely to produce adequate anticoagulation (peak anti-factor Xa 0.3 IU/mL or greater) when compared with fixed-dose enoxaparin (44.3% vs 48.2%, P = .67). Weight-tiered enoxaparin was not more likely to avoid over-anticoagulation (peak anti-factor Xa 0.5 IU/mL or greater) when compared with fixed-dose enoxaparin (3.3% vs 3.6%, P = 1.00). The groups had no significant difference in trough anti-factor Xa. Observed rates of 90-day symptomatic venous thromboembolism and clinically relevant bleeding were low (0% and 3.1%, respectively) and were not significantly different between groups.

CONCLUSIONS

This multicenter pre/post clinical trial did not show a pharmacokinetic advantage to weight-tiered enoxaparin, when compared with fixed-dose enoxaparin, in thoracic surgery patients. (Clinicaltrials.gov identifier: NCT03251963.).

Underdosing of Prophylactic Enoxaparin Is Common in Orthopaedic Trauma and Predicts 90-Day Venous Thromboembolism

OBJECTIVES

To determine the feasibility and impact of real-time anti-factor Xa (aFXa) level monitoring and enoxaparin dose adjustment in orthopaedic trauma. To examine the adequacy of standard fixed-dose enoxaparin chemoprophylaxis and to examine whether patient-specific factors influence enoxaparin metabolism.

DESIGN

Prospective cohort.

SETTING

Academic Level-I trauma center.

PATIENTS

Postoperative adult orthopaedic trauma patients undergoing acute fracture or nonunion surgery of the pelvis, acetabulum, or lower extremity placed on 30 mg of enoxaparin twice daily.

INTERVENTION

Peak steady-state aFXa levels were drawn with a goal range of 0.2-0.4 IU/mL. Patients with out-of-range levels underwent a 10-mg dose adjustment followed by repeat aFXa draws.

MAIN OUTCOME MEASURES

Peak and trough aFXa levels, 90-day venous thromboembolism, and bleed events.

RESULTS

Of 109 enrolled patients, 43% had inadequate initial peak aFXa levels (aFXa < 0.2 IU/mL) with standard dosing. Higher gross weight, acetabular surgery, and operation length predicted low aFXa levels (P < 0.001, 0.006, 0.004, respectively). Dose adjustment increased the proportion of patients with in-range aFXa levels from 53.2% to 87.8% (P < 0.001). Patients with low aFXa levels during hospitalization or at discharge had significantly higher 90-day deep vein thrombosis and pulmonary embolism rates compared to those with adequate aFXa levels (deep vein thrombosis 12% vs. 1.36%; P = 0.023, pulmonary embolism 8% vs. 0%; P = 0.027). There were no major bleed events.

CONCLUSIONS

Patients receiving inadequate enoxaparin chemoprophylaxis were at significantly increased risk of 90-day venous thromboembolism. Standard fixed-dose enoxaparin provided inadequate chemoprophylaxis in 43% of postoperative orthopaedic trauma patients, which significantly improved with dose adjustment. Weight, acetabular surgery, and operation length predicted inadequate enoxaparin prophylaxis.

LEVEL OF EVIDENCE

Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

Association of Anti-Factor Xa-Guided Dosing of Enoxaparin With Venous Thromboembolism After Trauma

Importance

The efficacy of anti-factor Xa (anti-Xa)-guided dosing of thromboprophylaxis after trauma remains controversial.

Objective

To assess whether dosing of enoxaparin sodium based on peak anti-Xa levels is associated with the venous thromboembolism (VTE) rate after trauma.

Design, Setting, and Participants

Retrospective review of 950 consecutive adults admitted to a single level I trauma intensive care unit for more than 48 hours from December 1, 2014, through March 31, 2017. Within 24 hours of admission, these trauma patients were screened with the Greenfield Risk Assessment Profile (RAP) (possible score range, 0-46). Patients younger than 18 years and those with VTE on admission were excluded, resulting in a study population of 792 patients.

Exposures

The control group received fixed doses of either heparin sodium, 5000 U 3 times a day, or enoxaparin sodium, 30 mg twice a day. The adjustment cohort initially received enoxaparin sodium, 30 mg twice a day. A peak anti-Xa level was drawn 4 hours after the third dose. If the anti-Xa level was 0.2 IU/mL or higher, no adjustment was made. If the anti-Xa level was less than 0.2 IU/mL, each dose was increased by 10 mg. The process was repeated up to a maximum dose of 60 mg twice a day.

Main Outcomes and Measures

Rates of VTE were measured. Venous duplex ultrasonography and computed tomographic angiography were used for diagnosis.

Results

The study population comprised 792 patients with a mean (SD) age of 46 (19) years and was composed of 598 men (75.5%). The control group comprised 570 patients, was older, and had a longer time to thromboprophylaxis initiation. The adjustment group consisted of 222 patients, was more severely injured, and had a longer hospital length of stay. The mean (SD) RAP scores were 9 (4) for the control group and 9 (5) for the adjustment group (P = .28). The VTE rates were similar for both groups (34 patients [6.0%] vs 15 [6.8%]; P = .68). Prophylactic anti-Xa levels were reached in 119 patients (53.6%) in the adjustment group. No difference in VTE rates was observed between those who became prophylactic and those who did not (7 patients [5.9%] vs 8 [7.8%]; P = .58). To control for confounders, 132 patients receiving standard fixed-dose enoxaparin were propensity matched to 84 patients receiving dose-adjusted enoxaparin. The VTE rates remained similar between the control and adjustment groups (3 patients [2.3%] vs 3 [3.6%]; P = .57).

Conclusions and Relevance

Rates of VTE were not reduced with anti-Xa-guided dosing, and almost half of the patients never reached prophylactic anti-Xa levels; achieving those levels did not decrease VTE rates. Thus, other targets, such as platelets, may be necessary to optimize thromboprophylaxis after trauma.

Inability to predict subprophylactic anti-factor Xa levels in trauma patients receiving early low-molecular-weight heparin

BACKGROUND

Standard low-molecular-weight heparin dosing may be suboptimal for venous thromboembolism prophylaxis. We aimed to identify independent predictors of subprophylactic Xa (subXa) levels in trauma patients treated under a novel early chemoprophylaxis algorithm.

METHODS

A retrospective analysis of trauma patients from July 2016 to June 2017 who received enoxaparin 40 mg twice daily and had peak Xa levels drawn was performed. Patients were divided into cohorts based on having a subXa (<0.2 IU/mL) or prophylactic (≥0.2 IU/mL) Xa level.

RESULTS

In all, 124 patients were included, of which 38 (31%) had subXa levels, and 17 (14%) had Xa levels greater than 0.4 IU/mL. Of the subXa cohort, 35 (92%) had their dosage increased, and the repeat Xa testing that was done in 32 revealed that only 75% reached prophylactic levels. The median time to the initiation of chemoprophylaxis was 21.9 hours (interquartile range [IQR], 11.45-35.07 hours). Patients who were defined as having lower risk of having a complication as a result of bleeding had a shorter time to starting prophylaxis than those at higher risk (18.39 hours [IQR 5.76-26.51 hours] vs. 29.5 hours [IQR 16.23-63.07 hours], p < 0.01).There was no difference in demographics, weight, body mass index, creatinine, creatinine clearance, injury severity score, type of injury, weight-based dose, time to chemoprophylaxis, or bleeding complications between the cohorts. No independent predictors of subXa level were identified on multivariable logistic regression.

CONCLUSIONS

A significant number of trauma patients fail to achieve prophylactic Xa levels. Intrinsic factors may prevent adequate prophylaxis even with earlier administration and higher dosing of low-molecular-weight heparin.

LEVEL OF EVIDENCE

Therapeutic, level IV.

Double-Blind Randomized Clinical Trial to Examine the Pharmacokinetic and Clinical Impacts of Fixed Dose versus Weight-based Enoxaparin Prophylaxis: A Methodologic Description of the FIxed or Variable Enoxaparin (FIVE) Trial

Venous thromboembolism is an important patient safety in plastic surgery, and multiple clinical trials in the past 10 years have provided increased understanding of the risks and benefits of venous thromboembolism prevention strategies. This paper provides an exhaustive discussion of the rationale behind and methodology for an in progress randomized double-blind clinical trial in plastic surgery inpatients, in which the 2 study arms are enoxaparin 40 mg twice daily and enoxaparin 0.5 mg/kg twice daily. The trial's primary aims are to: (1) demonstrate whether enoxaparin 0.5 mg/kg twice daily is superior to enoxaparin 40 mg twice daily for the pharmacokinetic endpoint of overanticoagulation (anti-Factor Xa > 0.4 IU/mL) and (2) demonstrate whether enoxaparin 0.5 mg/kg twice daily is not inferior to enoxaparin 40 mg twice daily for the pharmacokinetic endpoint of underanticoagulation (anti-Factor Xa < 0.2 IU/mL). The results of this trial will provide Level I evidence to help guide plastic surgeon's choice of postoperative prophylactic anticoagulation.

Anti-Xa guided enoxaparin dose adjustment improves pharmacologic deep venous thrombosis prophylaxis in burn patients

INTRODUCTION

Patients recovering from burn injury are at high risk of developing deep venous thrombosis (DVT). While 30-mg twice-daily enoxaparin is accepted as the standard prophylactic dose, recent evidence in injured patients suggests this dosing strategy may result in sub-optimal pharmacologic DVT prophylaxis. We hypothesized that standard enoxaparin dosing would result in inadequate DVT prophylaxis in burn patients.

METHODS

A retrospective review of an ABA-verified Burn center's registry from January 2012 - December 2016 identified patients with peak plasma anti-Xa levels to monitor the efficacy of pharmacologic DVT prophylaxis. Patients ≥18 years old were included if they received at least 3 doses of enoxaparin and had appropriately timed peak anti-Xa levels. We analyzed data including patient demographics, body weight, body mass index (BMI) and total body surface area burn (TBSA). Diagnosis of DVT was collected.

RESULTS

During the study period, 393 patients were screened with a plasma anti-Xa levels. Of the 157 patients that met inclusion criteria, 81 (51.6%) achieved target peak plasma anti-Xa levels (0.2-0.4 IU/mL) on standard 30-mg twice-daily prophylactic enoxaparin and 76 (48.4%) had sub-prophylactic levels. Sub-prophylactic patients were more likely to be male, have increased body weight and elevated BMI. 49 of the 76 sub-prophylactic patients received a dose-adjustment in order to reach target anti-Xa levels; 37 patients required 40mg twice-daily, 10 required 50mg twice-daily and 2 required 60mg twice-daily. The overall DVT rate was 3.8%.

CONCLUSIONS

The current recommended prophylactic dose of 30-mg twice-daily enoxaparin is inadequate in many burn patients. Alternate dosing strategies should be considered to increase the number of burn patients achieving target prophylactic anti-Xa levels. Determining whether prophylactic enoxaparin dose adjustment decreases DVT rates in burn injured patients should be evaluated in future prospective trials.

Twice-Daily Enoxaparin among Plastic Surgery Inpatients: An Examination of Pharmacodynamics, 90-Day Venous Thromboembolism, and 90-Day Bleeding

BACKGROUND

Low anti-factor Xa level, indicative of inadequate enoxaparin dosing, has a significant association with 90-day venous thromboembolism events. The authors examined the pharmacodynamics of enoxaparin 40 mg twice daily and its correlation with anti-factor Xa level, postoperative venous thromboembolism, and bleeding.

METHODS

Adult patients were admitted after plastic and reconstructive surgery and received enoxaparin 40 mg twice daily. Peak anti-factor Xa levels, which quantify enoxaparin's antithrombotic effect, were drawn, with a goal level of 0.2 to 0.4 IU/ml. Ninety-day symptomatic venous thromboembolism and clinically relevant bleeding were identified.

RESULTS

The authors enrolled 118 patients who received enoxaparin 40 mg twice daily. Of these patients, 9.6 percent had low peak anti-factor Xa levels (<0.2 IU/ml), 62.6 percent had in-range peak anti-factor Xa levels (0.2 to 0.4 IU/ml), and 27.8 percent had high anti-factor Xa levels (>0.4 IU/ml). With enoxaparin 40 mg twice daily, 90.4 percent of patients received at least adequate prophylaxis. Patient weight predicted the rapidity of enoxaparin metabolism. Zero acute 90-day venous thromboembolism occurred. Eight patients (6.8 percent) had clinically relevant 90-day bleeding: clinical consequences ranged from cessation of enoxaparin prophylaxis to transfusion to operative hematoma evacuation.

CONCLUSIONS

When enoxaparin 40 mg twice daily is provided, 90 percent of patients receive at least adequate venous thromboembolism prophylaxis (anti-factor Xa level >0.2 IU/ml). However, 27 percent of the overall population is overtreated (anti-factor Xa level >0.4 IU/ml). These pharmacodynamics data likely explain the low rate of 90-day acute venous thromboembolism (0 percent) and the high rate of clinically relevant bleeding (6.8 percent) observed. Future studies are needed to better optimize the risks and benefits of enoxaparin prophylaxis in plastic and reconstructive surgery patients.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Weight-based enoxaparin dosing and deep vein thrombosis in hospitalized trauma patients: A double-blind, randomized, pilot study

BACKGROUND

Venous thromboembolism is a cause of morbidity and mortality in trauma patients. Chemoprophylaxis with low-molecular-weight heparin at a standardized dose is recommended. Conventional chemoprophylaxis may be inadequate. We hypothesized that a weight-adjusted enoxaparin prophylaxis regimen would reduce the frequency of venous thromboembolism in hospitalized trauma patients and at 90-day follow-up.

METHODS

This prospective, randomized pilot study enrolled adult patients admitted to a level 1 trauma center between July 2013 and January 2015. Subjects were randomized to receive either standard (30 mg subcutaneously every 12 hours) or weight-based (0.5mg/kg subcutaneously every 12 hours) enoxaparin. Surveillance duplex ultrasound for lower extremity deep vein thrombosis was performed on hospital days 1, 3, and 7, and weekly thereafter. The primary outcome was deep vein thrombosis during hospitalization. Secondary outcomes included venous thromboembolism at 90 days and significant bleeding events.

RESULTS

Two hundred thirty-four (124 standard, 110 weight-based) subjects were enrolled. There was no difference between standard and weight-based regarding age, body mass index, percentage female gender, injury severity score, or percentage that had surgery. There was a trend toward less in-hospital deep vein thrombosis in weight-based (12 [9.7%] standard vs 4 [3.6%] weight-based, P = .075). At 90 days, there was no difference in venous thromboembolism (12 [9.7%] standard vs 6 [5.5%] weight-based, P =.34). There was 1 bleeding event, which occurred in a standard subject.

CONCLUSION

Weight-based enoxaparin dosing for venous thromboembolism chemoprophylaxis in trauma patients may provide better protection against venous thromboembolism than standard. A definitive study is necessary to determine whether weight-based dosing is superior to standard.

Enoxaparin 40 mg per Day Is Inadequate for Venous Thromboembolism Prophylaxis After Thoracic Surgical Procedure

BACKGROUND

Many patients undergoing thoracic surgical procedures have venous thromboembolism (VTE) events despite the receipt of chemical prophylaxis. Enoxaparin's pharmacologic impact can be quantified by using anti-Factor Xa (aFXa) levels. We hypothesized that enoxaparin 40 mg once daily would be inadequate for most inpatients undergoing thoracic surgical procedures and that a real-time dose adjustment algorithm would be effective.

METHODS

This prospective clinical trial enrolled inpatients who were to undergo a thoracic surgical procedure and placed on enoxaparin 40 mg once daily for VTE prophylaxis after surgical procedures. aFXa levels were used to measure the anticoagulant effect of enoxaparin once steady state had been reached. Patients whose aFXa levels were out of range received real-time enoxaparin dose adjustment and had repeat aFXa levels drawn.

RESULTS

Ninety-three inpatients undergoing thoracic surgical procedures were prospectively enrolled. The majority of patients (67.4%) had low peak aFXa levels (<0.3 IU/mL), indicative of inadequate enoxaparin prophylaxis, and 30.3% of patients had in-range aFXa levels (0.3 to 0.5 IU/mL). Patient weight had a moderate correlation (r² 0.38) with peak aFXa level. Patient weight, female sex, and preoperative creatinine were independent predictors of peak aFXa in a linear regression model. Real-time, protocol-driven enoxaparin dose adjustment allowed a significantly increased proportion of patients to achieve in-range aFXa levels (30.3% vs 97.6%, p < 0.001).

CONCLUSIONS

Enoxaparin 40 mg once daily is inadequate for most inpatients undergoing thoracic surgical procedures, based on a pharmacodynamic study of aFXa levels. Future research should examine the impact of weight-based once daily enoxaparin dosing versus twice daily enoxaparin dosing on prophylaxis adequacy.

Relation of antifactor-Xa peak levels and venous thromboembolism after trauma

BACKGROUND

No previous studies have established the optimal antifactor Xa (anti-Xa) level to guide thromboprophylaxis (TPX) dosing with enoxaparin in trauma patients. We hypothesize that achieving 0.2-0.4 IU/mL anti-Xa will decrease venous thromboembolism (VTE) rates after trauma.

METHODS

This was a retrospective review of 194 intensive care unit patients sustaining blunt or penetrating trauma from January 2015 to March 2017. All received initial enoxaparin (30 mg BID subcutaneous) and mechanical devices for TPX. Peak anti-Xa levels were drawn after each third dose. The enoxaparin dose was adjusted up to a maximum of 60 mg BID subcutaneous until a peak level of 0.2-0.4 IU/mL was achieved. Data are expressed as mean ± SD if parametric or median (IQR) if not.

RESULTS

The Greenfield Risk Assessment Profile score was 9 ± 4, Injury Severity Score 23 ± 14, and hospital length of stay 19 (11-38) days. The overall VTE rate was 7.2% (n = 14), with 10 deep venous thromboses (DVT) and 5 pulmonary emboli (PE). One patient had both a DVT and PE. The median time to VTE diagnosis was 14 (7-17) days. In those diagnosed with a VTE, 50.0% (n = 7) never reached 0.2-0.4 IU/mL anti-Xa and 42.8% (n = 6) were diagnosed with a VTE after achieving these levels. Prophylactic levels were achieved initially in 64 (33.0%) patients, and achieved later in 38 (19.6%) additional patients, giving an overall prophylactic rate of 52.6% (n = 102). There were no differences in VTE (6.9% vs. 7.6%, p = 0.841), DVT (3.9% vs. 6.5%, p = 0.413), or PE (3.9% vs. 1.1%, p = 0.213) rates between those who became prophylactic and those who did not.

CONCLUSIONS

There was no difference in VTE incidence between those achieving anti-Xa peak levels of 0.2-0.4 IU/mL and those who did not. Furthermore, these levels were never achieved in some trauma patients despite repeated dosing over a >10-day period.

LEVEL OF EVIDENCE

Therapeutic study, level IV.

Weight-Based Dosing for Once-Daily Enoxaparin Cannot Provide Adequate Anticoagulation for Venous Thromboembolism Prophylaxis

BACKGROUND

Surgeons commonly provide enoxaparin prophylaxis to high-risk patients to decrease venous thromboembolism risk. The authors' prior work demonstrated that most patients receive inadequate venous thromboembolism prophylaxis, based on anti-factor Xa level, when enoxaparin 40 mg/day is provided and that peak anti-factor Xa level correlates with weight. This study models a weight-based strategy for daily enoxaparin prophylaxis and its impact on anti-factor Xa levels.

METHODS

The authors enrolled plastic surgery patients who received enoxaparin 40 mg/day and had anti-factor Xa levels drawn. The enoxaparin dose of 40 mg was converted to a milligram-per-kilogram dose for each patient. Stratified analysis examined the milligram-per-kilogram dose that produced low, in-range, and high anti-factor Xa levels to identify the appropriate milligram-per-kilogram dose to optimize venous thromboembolism prevention and bleeding events.

RESULTS

Among 94 patients, weight-based dosing ranged from 0.28 to 0.94 mg/kg once daily. For peak and trough anti-factor Xa levels, there was nearly complete overlap for milligram-per-kilogram dosing that produced low versus in-range anti-factor Xa levels. For peak anti-factor Xa, there was nearly complete overlap for milligram-per-kilogram dosing that produced in-range versus high anti-factor Xa levels. Mean milligram-per-kilogram dose was not significantly different between patients who did or did not have postoperative venous thromboembolism (0.41 mg/kg versus 0.52 mg/kg; p = 0.085) or clinically relevant bleeding (0.48 mg/kg versus 0.51 mg/kg; p = 0.73).

CONCLUSIONS

Alterations in enoxaparin dose magnitude based on patient weight cannot allow a high proportion of patients to achieve appropriate anti-factor Xa levels when once-daily enoxaparin prophylaxis is provided. Future research should examine the impact of increased enoxaparin dose frequency on anti-factor Xa levels, venous thromboembolism events, and bleeding.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Prophylactic enoxaparin doses may be inadequate in patients undergoing abdominal cancer surgery

BACKGROUND

The incidence of venous thromboembolism has increased in patients following cancer surgery despite the increased use of prophylactic anticoagulants, suggesting standard doses may be inadequate. We sought to determine the adequacy of enoxaparin prophylaxis in patients undergoing abdominal cancer surgery.

METHODS

Peak and trough anti-Xa levels were measured in patients receiving enoxaparin thromboprophylaxis (40 mg daily or 30 mg twice daily, at the surgeon's discretion) after undergoing open abdominal cancer surgery at a single institution.

RESULTS

Fifty-five patients received enoxaparin 40 mg daily (group 1), 18 received 30 mg twice daily (group 2; total n = 73). There were no significant differences in gender, age, body mass index, creatinine clearance, diagnosis, or procedure between the two groups. Thirty-nine patients (53.4%) had inadequate peak anti-Xa levels (<0.2 IU/mL) and 69 patients (94.5%) had inadequate trough levels (≤0.1 IU/mL). Group 2 had lower mean peak levels (0.14 ± 0.02 IU/mL) than group 1 (0.22 ± 0.01, P = 0.003), and higher mean trough levels (0.06 ± 0.017) than group 1 (0.02 ± 0.004, P = 0.033). Group 2 had lower incidence of adequate peak anti-Xa levels than group 1 when adjusting for gender, age, body mass index, and preoperative creatinine clearance (OR 0.23, P = 0.039).

CONCLUSIONS

The majority of patients had inadequate anti-Xa levels following abdominal cancer surgery, calling into question standard prophylactic enoxaparin dosing.

Individualized Venous Thromboembolism Risk Stratification Using the 2005 Caprini Score to Identify the Benefits and Harms of Chemoprophylaxis in Surgical Patients: A Meta-analysis

OBJECTIVE

We performed a meta-analysis to investigate benefits and harms of chemoprophylaxis among surgical patients individually risk stratified for venous thromboembolism (VTE) using Caprini scores.

SUMMARY OF BACKGROUND DATA

Individualized VTE risk stratification may identify high risk surgical patients who benefit from peri-operative chemoprophylaxis.

METHODS

MEDLINE, EMBASE, and the Cochrane Library (CENTRAL) databases were queried. Eligible studies contained data on postoperative VTE and/or bleeding events with and without chemoprophylaxis. Primary outcomes included rates of VTE and clinically relevant bleeding after surgical procedures, stratified by Caprini score. A meta-analysis was conducted using a random-effects model.

RESULTS

Among 13 included studies, 11 (n = 14,776) contained data for VTE events and 8 (n = 7590) contained data for clinically relevant bleeding with and without chemoprophylaxis. The majority of patients received mechanical prophylaxis. A 14-fold variation in VTE risk (from 0.7% to 10.7%) was identified among surgical patients who did not receive chemoprophylaxis, and patients at increased levels of Caprini risk were significantly more likely to have VTE. Patients with Caprini scores of 7 to 8 [odds ratio (OR) 0.60, 95% confidence interval (95% CI) 0.37-0.97] and >8 (OR 0.41, 95% CI 0.26-0.65) had significant VTE risk reduction after surgery with chemoprophylaxis. Patients with Caprini scores ≤6 comprised 75% of the overall population, and these patients did not have a significant VTE risk reduction with chemoprophylaxis. No association between postoperative bleeding risk and Caprini score was identified.

CONCLUSIONS

The benefit of peri-operative VTE chemoprophylaxis was only found among surgical patients with Caprini scores ≥7. Precision medicine using individualized VTE risk stratification helps ensure that chemoprophylaxis is used only in appropriate surgical patients and may minimize bleeding complications.

Anti-Factor Xa measurements in acute care surgery patients to examine enoxaparin dose

BACKGROUND

The purpose of this study was to determine if fixed dose enoxaparin prophylaxis provided effective anticoagulation for acute care surgery patients and to examine whether a real-time enoxaparin dose adjustment algorithm optimized anticoagulation.

METHODS

Acute care surgical patients placed on enoxaparin prophylaxis 30 mg twice daily were recruited prospectively. Peak steady state aFXa levels were drawn with a goal peak aFXa range of 0.2-0.4 IU/ml. A real time dose adjustment algorithm was implemented for patients with out-of-range levels.

RESULTS

Fifty five patients were included. 56.4% of patients had low aFXa levels (<0.2 IU/mL). Real-time enoxaparin dose adjustment significantly increased the proportion of patients who achieved in-range peak aFXa levels, compared to standard dosing (74.5% vs 41.8%, p < 0.001). Patients with initial inadequate peak aFXa levels had a higher rate of 90-day post-operative VTE, although not statistically significant (16.1% vs. 8.3%, p = 0.50).

CONCLUSION

The majority of acute care surgery patients receive inadequate VTE prophylaxis with fixed enoxaparin dosing.

Anti-Xa-guided enoxaparin thromboprophylaxis reduces rate of deep venous thromboembolism in high-risk trauma patients

BACKGROUND

Appropriate prophylaxis against venous thromboembolism (VTE) remains undefined. This study evaluated an anti-Xa-guided enoxaparin thromboprophylaxis (TPX) protocol on the incidence of VTE in high-risk trauma patients based on Greenfield's Risk Assessment Profile (RAP) score.

METHODS

This is a retrospective observational study of patients admitted to a trauma intensive care unit over a 12-month period. Patients were included if they received anti-Xa-guided enoxaparin TPX. Dosage was adjusted to a prophylactic peak anti-Xa level of 0.2 to 0.4 IU/mL. Subgroup analysis was performed on high-risk patients (RAP score ≥10) who received lower-extremity duplex ultrasound surveillance for deep vein thrombosis (DVT). Data are expressed as mean ± SD. Significance was assessed at p < 0.05.

RESULTS

One hundred thirty-one patients received anti-Xa-guided enoxaparin TPX. Four patients were excluded for age or acute VTE on admission. Fifty-six patients with RAP score of ≥10 and surveillance duplex evaluations were included in the subgroup analysis with mean age 43 ± 20 years, Injury Severity Score of 25 ± 10, and RAP score of 16 ± 4. Prophylactic anti-Xa levels were initially achieved in 34.6% of patients. An additional 25.2% required 40 to 60 mg twice daily to reach prophylactic levels; 39.4% never reached prophylactic levels. Weight, body mass index, ISS, and RAP score were significantly higher with subprophylactic anti-Xa levels. One patient developed bleeding complications (0.8%). No patient developed intracerebral bleeding or heparin-induced thrombocytopenia.Nine VTE events occurred in the high-risk subgroup, including four DVT (7.1%), all asymptomatic, and five pulmonary emboli (8.9%). The historical rate of DVT in similar patients (ISS 31 ± 12 and RAP score 16 ± 5) was 20.5%, a significant decrease (p = 0.031). Mean chest Abbreviated Injury Scale scores were significantly higher for patients developing pulmonary emboli than DVT, 3.0 ± 1.1 vs. 0.0 (p < 0.001).

CONCLUSIONS

Mean chest Abbreviated Injury Scale score was higher in patients developing pulmonary embolism. Increased weight, body mass index, ISS, and RAP score are associated with subprophylactic anti-Xa levels. Anti-Xa-guided enoxaparin dosing reduced the rate of DVT from 20.5% to 7.1% in high-risk trauma patients.

LEVEL OF EVIDENCE

Therapeutic study, level IV.

Inadequate Enoxaparin Dosing Predicts 90-Day Venous Thromboembolism Risk among Plastic Surgery Inpatients: An Examination of Enoxaparin Pharmacodynamics

BACKGROUND

Evidence-based plastic surgery guidelines support the effectiveness of once-daily enoxaparin prophylaxis. Despite prophylaxis, one in 25 highest risk patients has a venous thromboembolism event. The authors examined the pharmacodynamics of standard enoxaparin doses in plastic surgery patients to examine whether patient-level factors predict enoxaparin metabolism, whether inadequate enoxaparin dose predicts downstream venous thromboembolism events, and whether a pharmacist-driven dose-adjustment protocol was effective.

METHODS

The authors recruited adult plastic surgery patients who received postoperative enoxaparin at 40 mg/day. Steady-state peak anti-factor Xa levels, a marker of enoxaparin effectiveness and safety, were determined. Patients with out-of-range anti-factor Xa levels had real-time dose adjustment based on a written protocol. Patients were followed for 90-day venous thromboembolism events.

RESULTS

Ninety-four patients were recruited, and 44 percent had in-range peak anti-factor Xa levels in response to standard enoxaparin dosing. Patient-level factors including extent of surgical injury and gross weight were independent predictors of enoxaparin metabolism. Patients with low anti-factor Xa levels were significantly more likely to have 90-day venous thromboembolism (10.2 percent versus 0 percent; p = 0.041). Real-time dose adjustment allowed a significantly increased proportion of patients to have in-range levels (67.1 percent versus 44.3 percent; p = 0.002).

CONCLUSIONS

Based on pharmacodynamic data, the majority of plastic surgery patients receive inadequate enoxaparin prophylaxis using fixed dosing. Patient-level factors can predict how patients will metabolize enoxaparin, and patients who receive inadequate enoxaparin prophylaxis are significantly more likely to have downstream venous thromboembolism events. Individualization of enoxaparin prophylaxis may minimize perioperative venous thromboembolism risk and further improve patient safety after plastic and reconstructive surgery procedures.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Goal directed enoxaparin dosing provides superior chemoprophylaxis against deep vein thrombosis

INTRODUCTION

Optimal enoxaparin dosing for deep venous thrombosis (DVT) prophylaxis remains elusive. Prior research demonstrated that trauma patients at increased risk for DVT based upon Greenfield's risk assessment profile (RAP) have DVT rates of 10.8% despite prophylaxis. The aim of this study was to determine if goal directed prophylactic enoxaparin dosing to achieve anti-Xa levels of 0.3-0.5IU/ml would decrease DVT rates without increased complications.

MATERIALS AND METHODS

Retrospective review of trauma patients having received prophylactic enoxaparin and appropriately timed anti-Xa levels was performed. Dosage was adjusted to maintain an anti-Xa level of 0.3-0.5IU/ml. RAP was determined on each patient. A score of ≥5 was considered high risk for DVT. Sub-analysis was performed on patients who received duplex examinations subsequent to initiation of enoxaparin therapy to determine the incidence of DVT.

RESULTS

306 patients met inclusion criteria. Goal anti-Xa levels were met initially in only 46% of patients despite dosing of >40mg twice daily in 81% of patients; however, with titration, goal anti-Xa levels were achieved in an additional 109 patients (36%). An average enoxaparin dosage of 0.55mg/kg twice daily was required for adequacy. Bleeding complications were identified in five patients (1.6%) with three requiring intervention. There were no documented episodes of HIT. Subsequent duplex data was available in 197 patients with 90% having a RAP score >5. Overall, five DVTs (2.5%) were identified and all occurred in the high-risk group. All patients were asymptomatic at the time of diagnosis.

CONCLUSION

An increased anti-Xa range of 0.3-0.5IU/ml was attainable but frequently required titration of enoxaparin dosage. This produced a lower rate of DVT than previously published without increased complications.

Review of current evidence available for guiding optimal Enoxaparin prophylactic dosing strategies in obese patients-Actual Weight-based vs Fixed

BACKGROUND

The current debate over the optimal Enoxaparin prophylactic dosing strategies in obese patients centre around whether it should be based on the actual weight of the patient (i.e. weight-based), or at an artificially fixed amount, as it is the case in Australia (40mg daily). The vast majority of the evidence available today is laboratory-based, measuring serum Antifactor-X_a activities as a marker for physiological response.

AIM

The aim of the parent study is to compare the clinical outcomes for obese patients who received fixed doses of enoxaparin compared to those who received weight-based doses within the licensed dosage recommendations. This review was conducted to examine whether a gap in knowledge exists in relation to dosing obese patients with enoxaparin as VTE prophylaxis after hospital admission to aid in development of the parent study concept.

METHOD

Databases such as Medline, EBSCOhost, ProQuest were interrogated using combinations of words such as "enoxaparin", AND "dosing strategy", AND "obese/obesity" AND "prophylaxis". Only eleven out of 14 primary studies which were considered to be sufficiently similar in methodology and anticipated outcomes were reviewed and analysed.

RESULTS

Pooled data from the eleven studies suggested that weight-based or higher-than-fixed dosing had a 36.2% higher success rate than fixed dosing, and was more likely to achieve the desired serum Anti-X_a activity levels (52.2% and 16% respectively). The rate of failure to achieve this is significantly lower in the weight-based groups (13.3%) than in fixed-dose groups (18.5%). These eleven studies reviewed included 601 patients in total.

CONCLUSION

There is insufficient evidence to support or negate the current enoxaparin health outcomes in obese and very obese patients due to the lack of post-discharge follow-up from hospitals. Further research is required to compare long-term outcomes after fixed and weight-based dosing of enoxaparin. The optimal dose of enoxaparin per kilogram of body weight for prophylaxis remains to be determined.

Increased Enoxaparin Dosing for Venous Thromboembolism Prophylaxis in General Trauma Patients

Objective: To review the evidence regarding increased enoxaparin dosing for venous thromboembolism (VTE) prophylaxis in the general trauma patient population. Data Sources: A search of MEDLINE databases (1946 to October 2016) was conducted using the search terms enoxaparin, thromboembolism prophylaxis, venous thromboembolism, trauma, anti-factor Xa, and weight-based dosing. Additional references were identified from a review of literature citations. Study Selection and Data Extraction: Search results were limited to English-language studies conducted in humans. Trials that included only obese patients or nontrauma patients were excluded. Data Synthesis: A total of 7 trials (958 patients) explored the use of increased dosing of enoxaparin for VTE prophylaxis in trauma patients. Patients were divided by enoxaparin dosing strategies: standard dosing of 30 mg twice daily (BID; n = 509), higher initial dosing regimen (n = 216), or dosing based on anti-FXa level adjustments (n = 233). The majority of the 42 total VTE events (64.3%) occurred in the standard dosing regimen. Within each group, VTE was reported in 5.3% of patients in the standard dosing group, 3.2% in the higher initial dosing group, and 4% in the anti-FXa adjustment group. Initial subtherapeutic anti-FXa levels occurred in 33% to 92% of standard dose patients and 9% to 39% of higher initial dose patients. The average weight-based dose required to achieve a therapeutic level ranged between 0.43 and 0.54 mg/kg/dose BID. The overall rate of bleeding was low, with 3 incidents (0.37%) reported. Conclusion: Standard-dose enoxaparin prophylaxis may not be optimal for the general trauma patient population. Weight-based enoxaparin dosing (0.5 mg/kg/dose BID) is an option in trauma patients considered to be at a lower risk of bleeding complications.

Supratherapeutic anti-factor Xa levels in patients receiving prophylactic doses of enoxaparin: A case series

INTRODUCTION

Enoxaparin prophylaxis prevents venous thromboembolism in surgical patients. Real time anti-Factor Xa monitoring for surgical patients on enoxaparin prophylaxis is increasingly common.

PRESENTATION OF CASES

We report on three cancer patients with therapeutic or supratherapeutic anti-Factor Xa levels while on prophylactic doses of enoxaparin after surgical procedures. In all cases, elevated anti-Factor Xa levels were the result of blood specimens being removed from a heparinized chemoport.

DISCUSSION

This case series highlights the importance of peripheral venipuncture or appropriate blood wasting from central access sites for anti-Factor Xa levels.

CONCLUSION

Inappropriately drawn anti-Factor Xa levels may contribute to prophylaxis interruption or unnecessary workup for renal or liver failure.

Utility of anti-factor Xa monitoring in surgical patients receiving prophylactic doses of enoxaparin for venous thromboembolism prophylaxis

BACKGROUND

Between 2% and 10% of the highest risk surgery, patients have a "breakthrough" venous thromboembolism (VTE) event despite receipt of chemoprophylaxis. The goals of this review are to summarize how patient-level factors may predict enoxaparin metabolism and how alterations in enoxaparin dose magnitude and frequency affect both anti-factor Xa (aFXa) levels and downstream VTE events.

DATA SOURCES

Relevant articles were identified on PubMed. Fixed-dose prophylaxis provides inadequate enoxaparin prophylaxis for most surgical patients based on anti-factor Xa levels. Inadequate enoxaparin dosing has been correlated with both asymptomatic and symptomatic VTE events. Patient-level factors such as gross weight and extent of injury predict enoxaparin metabolism. Weight-based or weight-tiered dosing regimens-and real-time dose adjustment based on anti-factor Xa levels-allow an increased proportion of patients to have in-range anti-factor Xa levels.

CONCLUSIONS

Inadequate enoxaparin dosing may explain why some patients have VTE despite enoxaparin prophylaxis. Ongoing research in the utility of weight-based or anti-factor Xa level driven enoxaparin dosing and dose adjustment is reasonable.