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The Limitations of Using a National Database to Investigate Risk Factors for Venous Thromboembolism

Swanson, Eric M.D.

Erratum

In the February 2016 issue, three of the references in the Letter “The Limitations of Using a National Database to Investigate Risk Factors for Venous Thromboembolism” (Plast Reconstr Surg. 2016;137:478e–479e) are incorrect. Reference 6 should read as follows: Swanson E. Prospective comparative clinical evaluation of 784 consecutive cases of breast augmentation and vertical mammaplasty, performed individually and in combination. Plast Reconstr Surg. 2013;132:30e–45e; discussion 46e–47e. Reference 9 as it appears in proof, by Kearon et al., should have been deleted. Finally, reference 10 should have been numbered as reference 9, Swanson E. Ultrasound screening for deep venous thrombosis detection: A prospective evaluation of 200 plastic surgery outpatients. Plast Reconstr Surg Glob Open 2015;3:e332. The publisher regrets these errors.

Plastic and Reconstructive Surgery. 137(4):1357, April 2016.

Plastic and Reconstructive Surgery: February 2016 - Volume 137 - Issue 2 - p 478e–479e
doi: 10.1097/01.prs.0000475809.12542.ef
Letters

Swanson Center, 11413 Ash Street, Leawood, Kans. 66211, eswanson@swansoncenter.com

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Sir:

Wes et al.1 mine a national database in an effort to identify risk factors for venous thromboembolism after body contouring surgery. Using current procedural terminology (CPT) codes, these investigators identify a number of risk factors: age, obesity, inpatient surgery, trunk contouring, a contaminated wound, and contouring more than two regions. The authors1 acknowledge that information regarding venous thromboembolism prevention is unavailable, so that no conclusion is possible regarding the efficacy, safety, or timing of chemoprophylaxis.

In their previous study,2 breast surgery patients accounted for 14.1 percent of the total. The patient makeup in this retrospective study is quite different, with 66.8 percent of the patients undergoing contouring of the breast.1 Breast procedures are normally considered separately from body contouring procedures.3 Unfortunately, the inclusion of mammaplasties skews the data analysis for the other 33.2 percent of patients undergoing body contouring surgery.

Thirty percent of the patients were treated by general surgeons.1 Unless general surgeons are performing breast contouring surgery, this means that most trunk contouring cases were performed by general surgeons. Almost half of the patients (and likely more if breast surgery patients were excluded) were obese, consistent with a large representation of bariatric patients.1 By contrast, obese patients account for about 20 percent of body contouring cases treated by plastic surgeons.4

The wound class and physical status data require explanation. Elective body contouring surgery should be a clean procedure. A clean-contaminated wound is a surgical wound in which the respiratory, alimentary, genital, or urinary tract is entered. In this database, 8.2 percent of patents were categorized as clean-contaminated, contaminated, or infected. All breast surgery (66.8 percent) is expected to be clean. Therefore, 24.7 percent (8.2/33.2) of patients undergoing body contouring surgery (excluding the breasts) had contaminated wounds.

The American Society of Anesthesiologists physical status classification5 for elective body contouring surgery is typically class 1 or 2. A patient labeled class 3 has a severe systemic disease, such as poorly controlled diabetes, chronic obstructive pulmonary disease, or morbid obesity (body mass index ≥ 40 kg/m2).5 This series included 3899 class 3 patients (21.9 percent), 220 class 4 patients (whose life is constantly threatened), and even two moribund class 5 patients.

The authors believe that their risk factors are “independent predictors,”1 but do not control for the procedure or history of massive weight loss. Bariatric patients have higher rates of anemia, hypertension, diabetes, and malnutrition. An apparent risk differential is created by including a large low-risk (and arguably unrelated) breast surgery group. Mammaplasty patients are, on average, younger and leaner6 than bariatric patients.1 Their operating times tend to be shorter.6 One cannot conclude that treating more than two areas with contouring is a risk factor if the majority of the low-risk breast surgery patients underwent breast surgery without simultaneous body contouring procedures. Patients undergoing contouring of more than two areas are more likely to be treated with an abdominoplasty, which places them at higher risk already. The same reasoning applies to age, sex (breast surgery patients being all female), and body mass index comparisons. To compare “apples with apples,” it would have been preferable to exclude breast patients (and, ideally, massive weight loss patients), or just study the breast patients. By the same logic, it is unfair to indict general surgeons because they are operating on a higher-risk patient group. Correlation does not imply causation; inpatients are admitted because they are at higher risk by virtue of a medical issue or the extent of planned surgery.

Data from the Venous Thromboembolism Prevention Study7 show that high-risk patients (Caprini score ≥ 7) experienced a 3.0 percent risk of venous thromboembolism, compared with a 1.2 percent risk overall.8 Wes et al.1 report a very similar complication rate, 2.95 percent, for their highest-risk group. The relevant question is whether anticoagulating 100 percent of these patients is justified if (1) 97 percent of the patients will not develop this complication1,8 (making the treatment unnecessary) and (2) the treatment introduces iatrogenic complications.8

Despite our best efforts, we cannot reliably predict who will develop a venous thromboembolism.8,9 Retrospective reviews of disparate patient groups, even large ones that do not include objective diagnostic data (and are affected by sampling bias),1 are unlikely to be fruitful. Our efforts are better directed at (1) improving anesthesia to reduce risk for all patients8 and (2) learning more about the natural history of this complication using ultrasound surveillance, which can also provide early detection and treatment for affected patients.9

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DISCLOSURE

The author has no financial interest to declare in relation to the content of this communication. There was no outside funding for this study.

Eric Swanson, M.D.

Swanson Center

11413 Ash Street

Leawood, Kans. 66211

eswanson@swansoncenter.com

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REFERENCES

1. Wes AM, Wink JD, Kovach SJ, Fischer JP. Venous thromboembolism in body contouring: An analysis of 17,774 patients from the National Surgical Quality Improvement databases. Plast Reconstr Surg. 2015;135:972e–980e
2. Fischer JP, Wes AM, Serletti JM, Kovach SJ. Complications in body contouring procedures: An analysis of 1797 patients from the 2005 to 2010 American College of Surgeons National Surgical Quality Improvement Program databases. Plast Reconstr Surg. 2013;132:1411–1420
3. Plastic and Reconstructive Surgery.Collections. Cosmetic: Body Contouring/Liposuction. Available at: http://journals.lww.com/plasreconsurg/pages/collectiondetails.aspx?TopicalCollectionId=10. Accessed May 30, 2015
4. Swanson E. Prospective clinical study reveals significant reduction in triglyceride level and white cell count after liposuction and abdominoplasty and no change in cholesterol levels. Plast Reconstr Surg. 2011;128:182e–197e
5. American Society of Anesthesiologists Physical Status Classification System. Available at: http://asahq.org/resources/clinical-information/asa-physical-status-classification-system. Accessed May 30, 2015
6. Swanson E. Local anesthetics in liposuction: Considerations for new practice advisory guidelines to improve patient safety. Plast Reconstr Surg. 2013;132:1075e–1077e
7. Pannucci CJ, Dreszer G, Wachtman CF, et al. Postoperative enoxaparin prevents symptomatic venous thromboembolism in high-risk plastic surgery patients. Plast Reconstr Surg. 2011;128:1093–1103
8. Swanson E. The case against chemoprophylaxis for venous thromboembolism prevention and the rationale for SAFE anesthesia. Plast Reconstr Surg Glob Open. 2014;2:e160
9. Kearon C, Akl EA, Comerota AJ, et al. Antithrombotic therapy for VTE disease: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e419S–e494S
    10. Swanson E. Ultrasound screening for deep venous thrombosis detection: A prospective evaluation of 200 plastic surgery outpatients. Plast Reconstr Surg Glob Open. 2015;3:e332
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