Breast Implants Decrease Chest Wall Trauma in Low-speed, Unrestrained Motor Vehicle Crash: An Experimental Model.

Breast implants improve quality of life in patients seeking improved breast aesthetics, and are known to minimize human injury in the less common scenario of penetrating trauma. People commonly sustain rib and sternum fractures and thoracic injury in motor vehicle crashes (MVC), a form of blunt traumatic injury. Whether breast implants minimize injury during MVC is unknown. This study examines the potential protective effect of breast implants in low speed, unrestrained MVC. Methods: Control (medical gel) and implant (medical gel with embedded breast implant) blocks were subjected to load approximating a low speed, 10mph MVC (n=12 blocks per group). Colormetric pressure film measured pressure at the neo-chest wall position in response to load, across the gel block base. Maximum pressure and average pressure across the gel block base were compared, by group. Results: Presence of an implant significantly decreased, by 22.8%, maximum pressure experienced by the neo-chest wall (333.0 ± 58.7 psi vs 431.6 ± 37.3 psi, p=0.0006). Average pressure experienced by the neo-chest wall across the gel block base was also significantly decreased, by 28.1%, in the implant group (53.4 ± 5.6 psi vs 74.3 ± 15.7 psi, p=0.0017). Subjective analysis of all implant and control blocks supported an overall reduction in pressure for the implant group. Conclusions: Presence of a breast implant decreased maximum pressure at the chest wall by 23%, and average pressure by 28%. Patients with breast implants involved in low speed, unrestrained MVC may be less likely to sustain rib and sternum fractures and thoracic injury, when compared to patients without implants.

Unfractionated Heparins, Low-Molecular-Weight Heparins, and Indirect Factor Xa Inhibitors in Plastic and Reconstructive Surgery: An Evidence-Based Review.

SUMMARY: Venous thromboembolism can present with devastating complications and sequalae, particularly in the surgical patient. Current data supports prophylactic anticoagulant use in the high-risk inpatient, defined as those with a 2005 Caprini Risk Assessment Model score of ≥7. The most utilized chemoprophylaxis agents include unfractionated heparin, low-molecular-weight heparins, and indirect factor Xa inhibitors. The authors review their mechanisms of action, metabolism, reversal agents, indications, contraindications, advantages, and disadvantages in plastic and reconstructive surgery.

The Majority of Venous Thromboembolism Events Should Occur in Lower Risk Aesthetic Surgery Patients: A Simulation Study.

Evidence-based venous thromboembolism (VTE) prevention among aesthetic patients is lacking. This study seeks to (1) quantify 2005 Caprini scores in primary breast augmentation patients, (2) determine the proportion of patients with potentially modifiable VTE risk factors, and (3) project, using Monte Carlo simulation, the expected distribution of Caprini scores among aesthetic surgery patients who develop VTE. Methods: The observational study (part 1) screened consecutive primary breast augmentation patients for VTE risk using the 2005 Caprini score. Aggregate scores were compiled, and the proportion of patients with potentially modifiable risk factors were identified. Part 2 used Monte Carlo simulation to generate risk score distributions for VTE events predicted to occur among randomly sampled patient cohorts with baseline Caprini risk profiles derived from the part 1 data. Results: One hundred patients had mean age of 35.7 years and mean body mass index of 23.8 kg/m2. Median 2005 Caprini score was 3 (range, 2-8), with the majority (96%) having scores of ≤6. Twenty-eight percent of patients had at least one potentially modifiable risk factor or risk factor potentially benefiting from further investigation. Monte Carlo simulations demonstrated that for a population with 96% Caprini ≤6 (and 4% Caprini ≥7), 80% of VTE events would be expected to occur in patients with Caprini scores ≤6. Conclusions: The majority of breast augmentation patients in this study (96%) have 2005 Caprini scores ≤6. Twenty-eight percent of patients have potentially modifiable risk factors. The majority of patients with VTE after aesthetic surgery are expected to have lower Caprini risk scores.

Outcomes of Prophylactic Enoxaparin Against Venous Thromboembolism in Hospitalized Children.

OBJECTIVES: To assess the biochemical and clinical outcomes of hospitalized children who received prophylactic enoxaparin. METHODS: We conducted a retrospective observational study of hospitalized children aged <18 years who received prophylactic enoxaparin against hospital-acquired venous thromboembolism (HA-VTE). Weight-based enoxaparin dosing was administered using a pharmacy-driven protocol, which later included a low molecular weight, anti-Xa level directed-dose adjustment strategy. Primary biochemical and clinical outcomes were achievement of goal anti-Xa range of 0.2 to 0.5 IU/mL and development of HA-VTE, respectively. Secondary clinical outcome was development of clinically relevant bleed. RESULTS: We analyzed 194 children with 13 (6.7%) infants aged <1 year and 181 (93.3%) older children aged ≥1 year. After the initial dose, only 1 (11.1%) infant, but 62 (57.9%) older children, achieved goal. Median number of anti-Xa levels until goal was 2 (interquartile range: 2-3) in infants and 1 (interquartile range: 1-2) in older children (P = .01). HA-VTE developed in 2 (15.4%) infants and 9 (5.0%) older children. Among children with anti-Xa level, HA-VTE developed less frequently in children who achieved (2.1%) than in those who did not achieve (13.6%) goal (P = .046). A total of 4 (2.1%) older children and no infants developed clinically relevant bleed. Among children with anti-Xa level, frequency of bleeding was comparable between children who did (3.2%) and did not achieve (0%) goal (P >.99). CONCLUSIONS: Our findings suggest the effectiveness and safety of an anti-Xa level directed strategy of prophylactic enoxaparin. However, this strategy should be investigated in prospective controlled studies.

Prevention of Venous Thromboembolism in Microvascular Surgery Patients Using Weight-Based Unfractionated Heparin Infusions.

BACKGROUND: Unfractionated heparin infusions are commonly used in microvascular surgery to prevent microvascular thrombosis. Previously, fixed-dose heparin infusions were believed to provide sufficient venous thromboembolism (VTE) prophylaxis; however, we now know that this practice is inadequate for the majority of patients. Anti-factor Xa (aFXa) level is a measure of unfractionated heparin efficacy and safety. This study evaluated the pharmacodynamics of weight-based dose heparin infusions and the impacts of real-time aFXa-guided heparin dose adjustments. METHODS: This prospective clinical trial enrolled adult microvascular surgery patients who received a weight-based heparin dose following a microsurgical procedure. Steady-state aFXa levels were monitored, and patients with out-of-range levels received dose adjustments. The study outcomes assessed were aFXa levels at a dose of heparin 10 units/kg/hour, time to adequate aFXa level, number of dose adjustments required to reach in-range aFXa levels, and clinically relevant bleeding and VTE at 90 days. RESULTS: Twenty-one patients were prospectively recruited, and usable data were available for twenty patients. Four of twenty patients (20%) had adequate prophylaxis at a heparin dose of 10 units/kg/hour. Among patients who received dose adjustments and achieved in-range aFXa levels, the median number of dose adjustments was 2 and the median weight-based dose was 11 units/kg/hour. The percentage of patients with in-range levels was significantly increased (65 vs. 15%, p = 0.0002) as a result of real-time dose adjustments. The rate of VTE at 90 days was 0%, and clinically relevant bleeding rate at 90 days was 15%. CONCLUSION: Weight-based heparin infusions at a rate of 10 units/kg/hour provide a detectable level of anticoagulation for some patients following microsurgical procedures, but most patients require dose adjustment to ensure adequate VTE prophylaxis.

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.

Incision Location Predicts 30-Day Major Adverse Events after Cosmetic Breast Augmentation: An Analysis of the Tracking Outcomes and Operations for Plastic Surgeons Database.

BACKGROUND: Enhanced understanding of early postoperative adverse events will improve patient counseling and preoperative risk modification to decrease complications in implant-based breast augmentation. This study seeks to evaluate the early major adverse events following cosmetic breast augmentation. METHODS: A retrospective cohort analysis of the Tracking Outcomes and Operations for Plastic Surgeons database was performed to identify any women undergoing augmentation mammaplasty with an implant between 2008 and 2016. RESULTS: A total of 84,296 patients were studied. Major adverse events were identified in 0.37 percent. Seroma requiring drainage was observed in 0.08 percent, hematoma requiring drainage was observed in 0.15 percent, deep wound disruption was observed in 0.09 percent, and implant loss was observed in 0.11 percent. The authors identified multiple independent predictors of major adverse events, including body mass index greater than 30 kg/m2 (relative risk, 2.05; p < 0.001), tobacco use (relative risk, 2.25; p < 0.001), and diabetes mellitus (relative risk, 1.8; p < 0.05). Use of a periareolar incision significantly increased the risk of developing an early postoperative complication (relative risk, 1.77; p < 0.001). CONCLUSIONS: The findings of this study indicate an early major adverse event rate following cosmetic breast augmentation with implants of 0.37 percent. The authors identified multiple independent predictors of major adverse events, including body mass index greater than 30 kg/m2, tobacco use, and diabetes mellitus. In addition, when controlling for other factors, periareolar incision significantly increased the risk for major adverse events, when compared to an inframammary incision. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Leveraging the Tracking Operations and Outcomes for Plastic Surgeons Database for Plastic Surgery Research: A "How-To" Guide.

SUMMARY: The Plastic Surgeries Registry Network supported by the American Society of Plastic Surgeons (ASPS) and the Plastic Surgery Foundation offers a variety of options for procedural data and outcomes assessment and research. The Tracking Operations and Outcomes for Plastic Surgeons (TOPS) database is a registry created for and used by active members of ASPS to monitor all types of procedural outcomes. It functions as a way for individual or group practices to follow surgical outcomes and constitutes a huge research registry available to ASPS members to access for registry-based projects. The TOPS registry was launched in 2002 and has undergone several iterations and improvements over the years and now includes more than 1 million procedure records. Although ASPS member surgeons have proven valuable assets in contributing their data to the TOPS registry, fewer have leveraged the database for registry-based research. This article overviews the authors' experience using the TOPS registry for a database research project to demonstrate the process, usefulness, and accessibility of TOPS data for ASPS member surgeons to conduct registry-based research. This article pairs with the report of the authors' TOPS registry investigation related to 30-day adverse events associated with incision location for augmentation mammaplasty.

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.

Estrogen Continuation and Venous Thromboembolism in Penile Inversion Vaginoplasty.

BACKGROUND: Estrogen therapy and penile inversion vaginoplasty (PIV) are necessary, life-saving interventions for many transfeminine patients. Patients undergoing PIV are generally at low baseline risk for venous thromboembolism (VTE) based on Caprini Score. Estrogen therapy may increase VTE risk in surgical patients, but its cessation may be psychiatrically dysphoric for transfeminine patients. AIM: This study examines whether perioperative estrogen cessation impacts VTE risk in patients undergoing PIV. METHODS: This was a pre-post study of patients undergoing PIV. From 2014 through 2018, all patients stopped estrogen therapy for 2 weeks before surgery and resumed 1 week postoperatively (group 1). Starting in 2019, all patients continued estrogen therapy perioperatively, with dose reductions for those whose dose was >6 mg/day (group 2). OUTCOMES: The primary outcome was 90-day VTE rate. RESULTS: 178 patients were included in the study, with 117 in group 1 and 61 in group 2. Median Caprini Score was 4 in group 1 (interquartile range: 3-6) and 3 in group 2 (interquartile range: 3-4) (P = .011). Complications per patient were higher in group 1 (2.2 vs 0.9, P < .001), with a longer follow-up (14.1 vs 10.2 months, P < .001). Rates of 90-day VTE were not different between groups (0.0% vs 1.6%, P = .166). CLINICAL IMPLICATIONS: Patients undergoing PIV are generally at low risk for VTE, based on 2005 Caprini Scores. This study provides preliminary evidence that perioperative estrogen therapy continuation does not appear to substantially increase VTE risk in transfeminine patients undergoing PIV with low Caprini Scores, although more investigation is needed to establish true safety. STRENGTHS & LIMITATIONS: Strengths include the pre-post design and single-surgeon experience, high proportion of patients with 90-day follow-up, and relatively large series to understand baseline VTE risk by Caprini Score in a PIV population. The main weakness of this study is its limited power to measure true differences in VTE risk based on estrogen continuation. CONCLUSIONS: This study suggests that perioperative estrogen continuation may be safe for patients undergoing PIV, the overwhelming majority of whom are at low baseline VTE risk. However, clinicians should weigh the magnitude of the risks and benefits of estrogen cessation on a case-by-case basis. Nolan IT, Haley C, Morrison SD, et al. Estrogen Continuation and Venous Thromboembolism in Penile Inversion Vaginoplasty. J Sex Med 2021;18:193-200.

Lateral Pectoralis Major Muscle Flap for Axillary Defect Obliteration.

This article describes the use of a lateral pectoralis major muscle flap for preemptive obliteration of axillary defects in breast cancer patients having reconstructive surgery. The muscle flap is based on a consistent lateral branch of the pectoral component of the thoracoacromial system. The flap is useful to improve axillary contour after sentinel lymph node biopsy or axillary lymph node dissection, and to cover lymphovenous anastomoses.

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.).

Postoperative Venous Thromboembolism Prophylaxis Utilizing Enoxaparin Does Not Increase Bleeding Complications After Abdominal Body Contouring Surgery.

BACKGROUND: Venous thromboembolism (VTE) chemoprophylaxis warrants an individualized, risk-stratified approach, and constitutes a relatively controversial topic in plastic surgery. OBJECTIVES: The aim of this study was to determine the safety of a 7-day postoperative enoxaparin regimen for VTE prophylaxis compared with a single preoperative dose of heparin in abdominal body contouring surgery. METHODS: This single-institution pre-post study investigated the safety of a 7-day enoxaparin postoperative regimen in abdominal body contouring procedures performed by a single surgeon from 2007 to 2018. Four procedures were included: traditional panniculectomy, abdominoplasty, fleur-de-lis panniculectomy, and body contouring liposuction. Group I patients received a single dose of 5000 U subcutaneous heparin in the preoperative period, and no postoperative chemical prophylaxis was administered. Group II patients received 40 mg subcutaneous enoxaparin in the immediate preoperative period, then once daily for 7 days postoperatively. RESULTS: A total of 195 patients were included in the study, 66 in Group I and 129 in Group II. The groups demonstrated statistically similar VTE risk profiles, based on the 2005 Caprini risk-assessment model. There were no statistically significant differences in the 2 primary outcomes: postoperative bleeding and VTE events. Group I patients had higher reoperation rates (22.7% vs 10.1%, P = 0.029), which was secondary to higher rates of revision procedures. CONCLUSIONS: A 7-day postoperative course of once-daily enoxaparin for VTE risk reduction in abdominal body contouring surgery does not significantly increase the risk of bleeding. Implementation of this regimen for postdischarge chemoprophylaxis, when indicated following individualized risk stratification, is appropriate.

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.

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.

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.