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.

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.

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.

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.

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.

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.

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.

LEVEL OF EVIDENCE: 4

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.

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.).

Cross-Leg Flaps for Lower Extremity Salvage: A Scoping Review

BACKGROUND

 Lower extremity trauma with soft tissue loss presents a challenge to the reconstructive surgeon. Cross-leg flaps, first described by Hamilton in 1854, are still used to salvage traumatized lower extremities in patients not suitable for free tissue transfer, or those who are receiving care in locations with limited resources.

METHODS

 A scoping review methodology was used to examine the evidence supporting the use of cross-leg flaps in modern healthcare.

RESULTS

 There have been 409 cases of cross-leg flaps reported in the modern literature, with the majority of flap cases occurring outside the United States in Turkey, India, and Japan. The most common indication was trauma, mentioned in 93.2% of patients (n = 353 of 379), and anatomic limitation, including inadequate vasculature, was the main reason for not performing free tissue transfer (52.8% of patients; n = 170 of 322). The majority are cross-leg fasciocutaneous flaps (85.8%, n = 273 of 318), based off the posterior tibial artery (27.5%, n = 50 of 182) and peroneal artery (26.9%, n =  49 of 182) and, covering defects of the distal third of the leg (55.5%, n = 151 of 272), or the foot (27.9%, n = 76 of 272). The pedicles are typically divided at 3 weeks (mean 20.9 days) after external fixation is used as the immobilization method (57.7%, n = 184 of 319). Flap survival was 100% across all publications except one (n = 349 of 350 patients), making cross-leg flaps a robust and reliable reconstructive option.

CONCLUSION

 In resource-limited environments or in patients who are unsuitable for microvascular free tissue transfer, the cross-leg flap remains an impactful and reliable option for limb salvage.

The Protective Effect of Breast Implants in Penetrating Trauma

Level of Evidence: 5

Venous Thromboembolism in Aesthetic Surgery: Risk Optimization in the Preoperative, Intraoperative, and Postoperative Settings

The purpose of this Continuing Medical Education (CME) article is to provide a framework for practicing surgeons to conceptualize and quantify venous thromboembolism risk among the aesthetic and ambulatory surgery population. The article provides a practical approach to identify and minimize venous thromboembolism risk in the preoperative, intraoperative, and postoperative settings.

Is release of the posterior lamella enough? A cadaveric exploration of posterior component separation techniques

BACKGROUND

As posterior component separation techniques continue to gain popularity there is uncertainty regarding the degree of fascial advancement afforded by the various techniques. Our study seeks to compare the degree anterior rectus sheath translation seen in full transversus abdominus release compared to simple release of the posterior lamella of the rectus sheath.

METHODS

Ten hemi-abdomens in five fresh cadavers were dissected. One hemi-abdomen underwent external oblique release. The contralateral hemi-abdomen underwent retrorectus dissection and initial release of the internal lamella of the internal oblique, followed by full transversus abdominus release. A 4 kg weight was suspended from the fascia and excursion was measured after 1) external oblique separation, 2) posterior lamella of the internal oblique separation, and 3) transversus abdominis separation.

RESULTS

Average unilateral hemifascial translation after release of the external oblique provided an average unilateral hemi-fascial translation of 3.38 cm (+/- 0.69). Release of the posterior lamella of the internal oblique provided 3.98 cm (+/- 0.94). After transversus release the average translation increased to 4.31 cm (+/- 0.89).

CONCLUSIONS

In this cadaveric study, the majority (92%) of fascial advancement afforded by posterior component separation was achieved by an intermediate step in the transversus abdominus release operation: division of the posterior lamella of the internal oblique.

Adequacy of Fixed-Dose Heparin Infusions for Venous Thromboembolism Prevention after Microsurgical Procedures

BACKGROUND

 In microvascular surgery, patients often receive unfractionated heparin infusions to minimize risk for microvascular thrombosis. Patients who receive intravenous (IV) heparin are believed to have adequate prophylaxis against venous thromboembolism (VTE). Whether a fixed dose of IV heparin provides detectable levels of anticoagulation, or whether the "one size fits all" approach provides adequate prophylaxis against VTE remains unknown. This study examined the pharmacodynamics of fixed-dose heparin infusions and the effects of real-time, anti-factor Xa (aFXa) level driven heparin dose adjustments.

METHODS

 This prospective clinical trial recruited adult microvascular surgery patients placed on a fixed-dose (500 units/h) unfractionated heparin infusion during their initial microsurgical procedure. Steady-state aFXa levels, a marker of unfractionated heparin efficacy and safety, were monitored. Patients with out-of-range aFXa levels received protocol-driven real-time dose adjustments. Outcomes of interest included aFXa levels in response to heparin 500 units/h, number of dose adjustments required to achieve goal aFXa levels, time to reach goal aFXa level, and 90-day clinically relevant bleeding and VTE.

RESULTS

 Twenty patients were recruited prospectively. None of 20 patients had any detectable level of anticoagulation in response to heparin infusions at 500 units/h. The median number of dose adjustments required to reach goal level was five, and median weight-based dose to reach goal level was 11.8 units/kg/h. Real-time dose adjustments significantly increased the proportion of patients with in-range levels (60 vs. 0%, p = 0.0001). The 90-day VTE rate was 5% and 90-day clinically relevant bleeding rate was 5%.

CONCLUSIONS

 Fixed-dose heparin infusions at a rate of 500 units/h do not provide a detectable level of anticoagulation after microsurgical procedures and are insufficient for the majority of patients who require VTE prophylaxis. Weight-based heparin infusions at 10 to 12 units/kg/h deserve future study in patients undergoing microsurgical procedures to increase the proportion of patients receiving adequate VTE prophylaxis.

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.

Comparison of face-to-face interaction and the electronic medical record for venous thromboembolism risk stratification using the 2005 Caprini score

OBJECTIVE

Perioperative venous thromboembolism (VTE) risk can be quantified with the 2005 Caprini score. The Caprini score has previously been validated by review of the electronic medical record (EMR) in >3000 plastic surgery patients. However, the accuracy of Caprini-based risk stratification using the EMR, as opposed to face-to-face contact with the patient, remains unknown.

METHODS

Plastic and reconstructive surgery patients who had surgery under general anesthesia, required postoperative admission, and were started on enoxaparin prophylaxis were identified. The 2005 Caprini scores were calculated retrospectively using EMR review only (no direct contact with the patients) to establish cohort 1. The 2005 Caprini scores were calculated prospectively using face-to-face interaction with the patients, followed by EMR review, to establish cohort 2. For all included patients, EMR review or face-to-face screening was personally performed by the authors. We compared the proportions of patients with identified Caprini risk factors and the aggregate risk scores of patients between cohorts.

RESULTS

Complete data were available for 536 unique patients in the EMR review cohort and 207 unique patients in the face-to-face cohort. Patients whose risk scores were calculated face to face had higher Caprini scores than those calculated by EMR review alone. The face-to-face cohort had a higher proportion of patients risk stratified as Caprini 7-8 (29.5% vs 24.8%) and Caprini >8 (26.6% vs 10.5%) compared with the EMR review cohort. Patients risk stratified by face-to-face discussion were significantly more likely to be stratified into a higher risk Caprini stratum. Face-to-face discussion identified a 2-fold increase in patients with personal history of deep venous thrombosis (12.6% vs 6.3%; P = .005), a 3-fold increase in patients with family history of VTE (16.9% vs 5.2%; P < .001), and a 20-fold increase in patients with personal history of multiple lost pregnancies (13.6% vs 0.6%; P < .001) compared with EMR review. Observed differences for family history of VTE and history of pregnancy loss persisted after propensity score analysis, created using component variables in the 2005 Caprini score plus gender; this supports the conclusion that observed differences were not due to site variation or case mix.

CONCLUSIONS

When it is used in isolation, the EMR may provide inaccurate estimation of patient-level VTE risk using the 2005 Caprini score. This study demonstrates that EMR review may miss key VTE risk factors, such as personal or family history of VTE, history of pregnancy loss, and others; this omission results in lower estimates of perioperative VTE risk. The importance of provider-patient interaction for accurate VTE risk stratification cannot be overstated.

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.

A Ballistics Examination of Firearm Injuries Involving Breast Implants

This ballistics study examines whether saline breast implants can decrease tissue penetration in firearm injuries. We hypothesize that the fluid column within a saline breast implant can alter bullet velocity and/or bullet pattern of mushrooming. The two experimental groups included saline implants with 7.4 cm projection and a no implant group. The experimental design allowed the bullet to pass-through an implant and into ballistics gel (n = 10) or into ballistics gel without passage through an implant (n = 11). Shots that passed through an implant had 20.6% decreased penetration distance when compared to shots that did not pass-through an implant; this difference was statistically significant (31.9 cm vs. 40.2 cm, p < 0.001). Implant group bullets mushroomed prior to gel entry, but the no implant group mushroomed within the gel. Bullet passage through a saline breast implant results in direct bullet velocity reduction and earlier bullet mushrooming; this causes significantly decreased ballistics gel penetration.

Use of Computerized Clinical Decision Support Systems to Prevent Venous Thromboembolism in Surgical Patients: A Systematic Review and Meta-analysis

Importance

Health care professionals do not adequately stratify risk or provide prophylaxis for venous thromboembolism (VTE) among surgical patients. Computerized clinical decision support systems (CCDSSs) have been implemented to assist clinicians and improve prophylaxis for VTE.

Objective

To evaluate the effect of implementing CCDSSs on the ordering of VTE prophylaxis and the rates of VTE.

Data Sources

PubMed, MEDLINE via OVID, EMBASE via OVID, Scopus, Cochrane CENTRAL Register of Controlled Trials, and clinicaltrials.gov were searched in June 2016 for articles published in English from October 15, 1991, to February 16, 2016. A manual search of references from relevant articles was also performed.

Study Selection

Clinical trials and observational studies among surgical patients comparing CCDSSs with VTE risk stratification and assistance in ordering prophylaxis vs routine care without decision support were included. Of the 188 articles screened, 11 (5.9%) were eligible for meta-analysis.

Data Extraction and Synthesis

Meta-analysis of Observational Studies in Epidemiology guidelines were followed. Two reviewers extracted data and assessed quality independently.

Main Outcomes and Measures

Rates of prophylaxis for VTE and VTE events. Random- and fixed-effects models were used to summarize odds ratios and risk ratios.

Results

Eleven articles (9 prospective cohort trials and 2 retrospective cohort trials) comprising 156 366 individuals (104 241 in the intervention group and 52 125 in the control group) were included. The use of CCDSSs was associated with a significant increase in the rate of appropriate ordering of prophylaxis for VTE (odds ratio, 2.35; 95% CI, 1.78-3.10; P < .001) and a significant decrease in the risk of VTE events (risk ratio, 0.78; 95% CI, 0.72-0.85; P < .001).

Conclusions and Relevance

Use of CCDSSs increases the proportion of surgical patients who were prescribed adequate prophylaxis for VTE and correlates with a reduction in VTE events.

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.

Validation of the Caprini Venous Thromboembolism Risk Assessment Model in Critically Ill Surgical Patients

IMPORTANCE

Appropriate risk stratification for venous thromboembolism (VTE) is essential to providing appropriate thromboprophylaxis and avoiding morbidity and mortality.

OBJECTIVE

To validate the Caprini VTE risk assessment model in a previously unstudied high-risk cohort: critically ill surgical patients.

DESIGN, SETTING, AND PARTICIPANTS

We performed a retrospective cohort study of 4844 adults (≥18 years old) admitted to a 20-bed surgical intensive care unit in a large tertiary care academic hospital during a 5-year period (July 1, 2007, through June 30, 2012).

MAIN OUTCOMES AND MEASURES

The main study outcome was VTE (defined as patients with deep vein thrombosis or pulmonary embolism) that occurred during the patient's initial hospital admission.

RESULTS

The study population was distributed among risk levels as follows: low, 5.3%; moderate, 19.9%; high, 31.6%; highest, 25.4%; and superhigh, 14.9%. The overall incidence of inpatient VTE was 7.5% and increased with risk level: 3.5% in low-risk patients, 5.5% in moderate-risk patients, 6.6% in high-risk patients, 8.6% in highest-risk patients, and 11.5% in superhigh-risk patients. Patients with Caprini scores greater than 8 were significantly more likely to develop inpatient VTE events when compared with patients with Caprini scores of 7 to 8 (odds ratio [OR], 1.37; 95% CI, 1.02-1.85; P = .04), 5 to 6 (OR, 1.35; 95% CI, 1.16-1.57; P < .001), 3 to 4 (OR, 1.30; 95% CI, 1.16-1.47; P < .001), or 0 to 2 (OR, 1.37; 95% CI, 1.16-1.64; P < .001). Similarly, patients with Caprini scores of 7 to 8 were significantly more likely to develop inpatient VTE when compared with patients with Caprini scores of 5 to 6 (OR, 1.33; 95% CI, 1.01-1.75; P = .04), 3 to 4 (OR, 1.27; 95% CI, 1.08-1.51; P = .005), or 0 to 2 (OR, 1.38; 95% CI, 1.10-1.74; P = .006).

CONCLUSIONS AND RELEVANCE

The Caprini VTE risk assessment model is valid. This study supports the use of individual risk assessment in critically ill surgical patients.

Feasibility of the internal mammary lymph node flap as a vascularized lymph node transfer: A cadaveric dissection study

BACKGROUND

We performed cadaveric dissections to examine the feasibility of an internal mammary-based lymph node flap as a donor site for vascularized lymph node transfer.

METHODS

Internal mammary vessels and adjacent nodes were dissected in ten fresh cadaver specimens. Surgeon inspection and palpation identified the number of nodes in the specimen. Specimens were examined macro- and microscopically by a pathologist for correlation of lymph node counts. Kappa statistic correlated surgeon- and pathologist-reported node counts.

RESULTS

Surgeon- and pathologist-reported node counts were moderately correlated (kappa 0.57). Inspection and palpation correctly predicted node presence or absence in 80% of specimens. Sixty percent of flaps contained between 1 and 3 nodes, with a mean of 2.0 nodes when nodes were present.

CONCLUSIONS

Inspection and palpation predicts the presence or absence of nodes in 80% of flaps. Nodes were present in 60% of internal mammary-based flaps, and one to three nodes can be transferred. © 2015 Wiley Periodicals, Inc. Microsurgery 36:485-490, 2016.

A validated risk model to predict 90-day VTE events in postsurgical patients

BACKGROUND

VTE is the proximate cause of 100,000 deaths in the United States each year. Perioperative VTE risk among surgical patients varies by 20-fold, which highlights the importance of risk stratification to identify high-risk patients, in whom chemoprophylaxis can decrease VTE risk, and low-risk patients, for whom the risk-benefit relationship of prophylaxis may be unfavorable.

METHODS

We used data from a statewide surgical quality collaborative for surgical procedures performed between 2010 and 2012. Regression-based techniques identified predictors of 90-day VTE while adjusting for procedural complexity and comorbid conditions. A weighted risk index was created and was validated subsequently in a separate, independent dataset.

RESULTS

Data were available for 10,344 patients, who were allocated randomly to a derivation or validation cohort. The 90-day VTE rate was 1.4%; 66.2% of the derivation cohort and 65.5% of the validation cohort received chemoprophylaxis. Seven risk factors were incorporated into a weighted risk index: personal history of VTE, current cancer, sepsis/septic shock/systemic inflammatory response syndrome, age≥60 years, BMI≥40 kg/m2, male sex, and family history of VTE. Prediction for 90-day VTE was similar in the derivation and validation cohorts (areas under the receiver operator curve, 0.72 and 0.70, respectively). An 18-fold variation in 90-day VTE rate was identified.

CONCLUSIONS

A weighted risk index quantifies 90-day VTE risk among surgical patients and identifies an 18-fold variation in VTE risk among the overall surgical population.

Inadequate venous thromboembolism risk stratification predicts venous thromboembolic events in surgical intensive care unit patients

BACKGROUND

Surgical intensive care unit (SICU) patients are known to be at high risk for venous thromboembolism (VTE). The 2005 Caprini Risk Assessment Model (RAM) predicts VTE risk in surgical patients. However, a physician's ability to accurately complete this RAM and the effect that inaccurate RAM completion might have on VTE risk remain unknown.

STUDY DESIGN

Between 2009 and 2012, physicians completed a 2005 Caprini score for all SICU admissions at our institution. For comparison, we used a previously validated, computer-generated score. Regression-based techniques examined the effect of inadequate risk stratification on inpatient VTE risk, when controlling for other confounders.

RESULTS

Among 3,338 consecutive SICU admissions, 55.2% had computer-generated scores that were higher than the physician-reported score, and 20.6% of scores were equal. Computer-generated scores were higher than physician-reported scores for both median (6 vs 5) and interquartile range (5 to 8 vs 3 to 7). Inter-rater reliability between the 2 scores was poor (kappa = 0.238). Risk score underestimation by ≥2 points was significantly associated with inpatient VTE (7.67% vs 4.59%, p = 0.002). Regression analysis demonstrated that each additional day's delay in chemoprophylaxis (odds ratio [OR] 1.05, 95% CI 1.01 to 1.08, p = 0.011) and under-risk stratification by ≥2 points (OR 2.46, 95% CI 1.53 to 3.96, p < 0.001) were independent predictors of inpatient VTE, as were higher admission APACHE score, personal history of VTE, recent pneumonia, and younger age.

CONCLUSIONS

Physicians under-risk stratify SICU patients when using the 2005 Caprini RAM. As hospitals incorporate electronic medical records into daily practice, computer-calculated Caprini scores may result in more accurate VTE risk stratification. Inadequate VTE risk assessment and delay to chemoprophylaxis carry independent and significant increased risk for VTE.

The role of full-thickness scalp resection for management of primary scalp melanoma

BACKGROUND

Scalp melanoma is aggressive and has a proclivity for regional metastasis. We hypothesize that subperiosteal scalp melanoma resection reduces in-transit/satellite recurrence, when compared with subgaleal resection.

METHODS

We identified patients with intermediate to deep, primary scalp melanoma referred to head/neck surgery over an 8-year period. Patients were compared based on scalp resection depth, including subperiosteal (resection to the level of calvarium) and subgaleal (resection including skin, subcutaneous tissue, and galea). The dependent variables were in-transit/satellite recurrence and time to in-transit/satellite recurrence.

RESULTS

Among 48 identified patients, the in-transit/satellite recurrence rate was 16.7%. Subgaleal resection patients had higher in-transit/satellite recurrence rates than subperiosteal resection patients (24.0% vs. 8.7%, P=0.155). Among node-negative patients, subgaleal resection had significantly higher in-transit/satellite metastasis rates when compared with subperiosteal resection (26.3% vs. 0%, P=0.047).

CONCLUSION

For node-negative, primary scalp melanoma, subperiosteal resection significantly decreases in-transit/satellite recurrence when compared with subgaleal resection. Given our small sample size, further studies are necessary to confirm these results.

Assessment of postoperative venous thromboembolism risk in plastic surgery patients using the 2005 and 2010 Caprini Risk score

BACKGROUND

Venous thromboembolism is an important patient safety issue. The authors sought to compare the predictive capacity of the 2005 and 2010 Caprini Risk Assessment Models for perioperative venous thromboembolism risk.

METHODS

The authors performed a retrospective, observational, crossover study using an established surgical outcomes database. A total of 3334 adult plastic surgery patients were identified. Patients were risk-stratified using both the 2005 and 2010 Caprini Risk Assessment Models. Each patient served as his or her own control, resulting in precise matching for identified and unidentified confounders. The outcome of interest was 60-day, symptomatic venous thromboembolism. The predictive capacities of the 2005 and 2010 Caprini risk scores were compared.

RESULTS

Use of the 2010 Caprini Risk Assessment Model resulted in a systematic increase in the aggregate risk score. The median 2010 Caprini score was significantly higher than the median 2005 Caprini score (6 versus 5, p<0.001). When compared with the 2010 model, the 2005 Caprini Risk Assessment Model was able to better separate the lowest and highest risk patients from one another. Patients classified as "super-high" risk (Caprini score>8) using the 2005 Caprini Risk Assessment Model were significantly more likely to have a 60-day venous thromboembolism event when compared with patients classified as super-high risk using the 2010 guidelines (5.85 percent versus 2.52 percent, p=0.021).

CONCLUSIONS

When compared with the 2010 Caprini Risk Assessment Model, the 2005 Caprini Risk Assessment Model provides superior risk stratification. The 2005 Caprini Risk Assessment Model is the more appropriate method to risk-stratify plastic surgery patients for perioperative venous thromboembolism risk.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, II.

Stratifying the risk of venous thromboembolism in otolaryngology

OBJECTIVE

The consequences of perioperative venous thromboembolism (VTE) are devastating; identifying patients at risk is an essential step in reducing morbidity and mortality. The utility of perioperative VTE risk assessment in otolaryngology is unknown. This study was designed to risk-stratify a diverse population of otolaryngology patients for VTE events.

STUDY DESIGN

Retrospective cohort study.

SETTING

Single-institution academic tertiary care medical center.

SUBJECTS AND METHODS

Adult patients presenting for otolaryngologic surgery requiring hospital admission from 2003 to 2010 who did not receive VTE chemoprophylaxis were included. The Caprini risk assessment was retrospectively scored via a validated method of electronic chart abstraction. Primary study variables were Caprini risk scores and the incidence of perioperative venous thromboembolic outcomes.

RESULTS

A total of 2016 patients were identified. The overall 30-day rate of VTE was 1.3%. The incidence of VTE in patients with a Caprini risk score of 6 or less was 0.5%. For patients with scores of 7 or 8, the incidence was 2.4%. Patients with a Caprini risk score greater than 8 had an 18.3% incidence of VTE and were significantly more likely to develop a VTE when compared to patients with a Caprini risk score less than 8 (P < .001). The mean risk score for patients with VTE (7.4) was significantly higher than the risk score for patients without VTE (4.8) (P < .001).

CONCLUSION

The Caprini risk assessment model effectively risk-stratifies otolaryngology patients for 30-day VTE events and allows otolaryngologists to identify patient subgroups who have a higher risk of VTE in the absence of chemoprophylaxis.

The effect of increased hip flexion using stirrups on lower-extremity venous flow: a prospective observational study

BACKGROUND

Patient positioning during surgeries for colorectal cancer may represent an unrecognized risk factor for deep venous thrombosis.

METHODS

Twelve healthy control patients were positioned supine with knee flexion at 90°. Duplex ultrasound examined common femoral vein (CFV) and proximal femoral vein diameter, peak systolic velocity, and volume flow with hip flexion at 0°, 30°, 60°, and 90°. Data were analyzed using the paired t test.

RESULTS

In the CFV, hip flexion to 90° was associated with a significant increase in mean volume flow when compared with hip flexion at 0° (.59 vs .36 L/min; P = .05) and 30° (.59 vs .35 L/min; P = .038). In both the CFV and proximal femoral vein, increased hip flexion was associated with significantly reduced vessel diameter and increased peak systolic velocity.

CONCLUSIONS

Intraoperative positioning of the lower extremities represents a modifiable risk factor for deep venous thrombosis. When stirrups are used, hip flexion of 90° maximizes venous drainage from the legs.

The effect of abdominal wall plication on intra-abdominal pressure and lower extremity venous flow: a case report

Abdominal wall plication is known to cause increased intra-abdominal pressure (IAP). Whether plication-associated increased IAP causes lower extremity venous stasis, a recognized risk factor for DVT, remains unknown. A 55-year-old woman had a unilateral pedicled TRAM procedure for mastectomy reconstruction. Prior to plication, duplex ultrasound measured proximal femoral vein (PFV) cross-sectional diameter and volume-flow. PFV measurements were repeated immediately after plication and on post-operative days (POD) 1, 2, and 4. Bladder pressure was measured at similar timepoints. PFV volume-flow decreased from 0.22 L/min to 0.16 L/min (73% of baseline) immediately post-plication and reached a nadir of 0.08 L/min (36% of baseline) on POD 2. Bladder pressure increased from 13 mm Hg to 19 mm Hg after plication, and peaked at 31 mm Hg after intra-operative trunk flexion to 30°. Thus, abdominal wall plication was associated with increased intra-abdominal pressure and ultrasound-documented lower extremity venous stasis that persisted for 48 h after surgery.