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A Rebuttal of Published Recommendations for Venous Thromboembolism Prophylaxis in Plastic Surgery

Swanson, Eric M.D.

Plastic and Reconstructive Surgery: November 2016 - Volume 138 - Issue 5 - p 951e–952e
doi: 10.1097/PRS.0000000000002695
Letters

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

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Sir:

Pannucci et al.1 describe their article both as a “systematic review and meta-analysis of controlled trials” and as a “consensus conference.” Systematic reviews typically include only studies with a high level of evidence, and are considered the highest level of evidence (Level I).2 A consensus conference, in contrast, represents collective expert opinion, the lowest level of evidence (Level V).2 Methodologic expertise was a stated criterion for authorship.1 Evidently, a favorable disposition to Caprini scores and chemoprophylaxis was also a prerequisite. The authors1 reference my articles challenging chemoprophylaxis3 and describing ultrasound surveillance as an alternative,4 but I was not invited to participate. The authors1 seek to build on previous guidelines5 that were careful not to make unsupported recommendations. Unfortunately, the authors’ conclusions reach beyond the evidence.

Pannucci et al.1 recommend that all plastic surgery patients should be risk-stratified using a 2005 Caprini score, evidently including outpatients. For patients with Caprini scores greater than 8, the authors1 recommend that surgeons consider chemoprophylaxis on an individual basis, relying on only two studies of hospitalized patients.6,7 Neither study was a controlled trial. The Level III Venous Thromboembolism Prevention Study6 compared an untreated historical control group with a prospective cohort of plastic surgery inpatients who received enoxaparin. The study by Bahl et al.,7 coauthored by Pannucci, was a retrospective chart review comparing venous thromboembolism risk in otolaryngologic surgery patients (11 percent undergoing plastic surgery procedures) treated with or without heparin. Even in these two studies,6,7 numerous confounders are at work, including diagnosis (particularly cancer), procedure, anesthesia, surgeon, anticoagulant, and the use of sequential compression devices.7 Both studies6,7 relied on chart reviews to calculate Caprini scores. As both teams have recognized in previous publications,8,9 this information (totaling 40 parameters6) is often incomplete in a retrospective chart review, leading to underestimated Caprini scores. This fact can explain a discrepancy in scores when comparing retrospective and prospective cohorts, undermining the case for statistical adjustments made in the Venous Thromboembolism Prevention Study.6 Adjusting for length of hospital stay without considering the duration of anticoagulation is also unjustified.3

Recently, Shaikh et al.10 attempted to find a significant risk difference using numerous Caprini scores as threshold values. The venous thromboembolism risk in “high-risk” patients with Caprini scores between 5 and 8 was 1.5 percent, the same as the overall risk.10 Counterintuitively, all 36 patients with extremely high Caprini scores (>10) experienced no cases of venous thromboembolism.10 Risk stratification models consistently provide a dismal 97 percent false-positive rate,6,10,11 much too high for a screening test.3 These findings should not be surprising. Caprini scores were not conceived scientifically and do not correlate with known relative risk values.12 Caprini scores do not consider the anesthesia method, which the authors acknowledge as an important risk factor.1

Bahl et al.7 report that patients who received chemoprophylaxis experienced a 1.2 percent risk of venous thromboembolism versus a 1.3 percent risk (difference nonsignificant) for patients who did not receive heparin—almost identical to the 1.2 percent rates for both treated and untreated patients in the Venous Thromboembolism Prevention Study.3 Bahl et al.7 also compared risk-stratified patients with Caprini scores greater than 7, finding a higher percentage of venous thromboembolism in the nontreated patients, but the difference was not significant. Despite its title, the Venous Thromboembolism Prevention Study6 also found no significant treatment benefit for risk-stratified patients. Nonsignificant differences (p = 0.08 for combined patients with Caprini scores >81) do not count as evidence. If there is no significant difference in risk,10 and no significant treatment benefit even among patients with higher Caprini scores,6,7 why calculate Caprini scores?

Pannucci et al.13 previously claimed that anticoagulation does not significantly increase reoperative hematoma rates. However, this analysis1 does find evidence for increased bleeding (p = 0.02). Bahl et al.7 reported higher rates of bleeding in anticoagulated patients (p < 0.001), similar to other studies in plastic surgery patients using either enoxaparin or rivaroxaban.14–17 The risk is not eliminated by avoiding a preoperative or intraoperative dose.7,17 A hematoma is a serious complication, not just an inconvenience.3 The authors1 cite 1999 guidelines18 recommending preoperative anticoagulation based on first principles and on data from other surgical specialties. However, ultrasonic evidence shows (surprisingly) that, in plastic surgery patients, deep venous thromboses do not typically develop during surgery.4

The authors1 cite two meta-analyses to support the use of sequential compression devices. However, only one study19 was conducted solely among surgical patients, and the authors reported significant publication bias. Pulmonary embolisms actually occurred more frequently (although not significantly) among treated patients. The evidence remains inconclusive.20

Recommending a randomized trial1 is impractical; equipoise is unlikely, particularly when the risk may be existential. It is time to move beyond making ineffective predictions and instead make use of highly accurate and noninvasive diagnostic imaging.4 Without this disruptive technology, venous thromboembolism research is analogous to the proverbial blind men examining an elephant.

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DISCLOSURE

The author has no financial interest in any of the products, devices, or drugs mentioned in this communication. The author has no conflicts of interest to disclose. There was no outside funding for this study.

Eric Swanson, M.D.

Swanson Center

11413 Ash Street

Leawood, Kan. 66211

eswanson@swansoncenter.com

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REFERENCES

1. Pannucci CJ, MacDonald JK, Ariyan S, et al. Benefits and risks of prophylaxis for deep venous thrombosis and pulmonary embolus in plastic surgery: A systematic review and meta-analysis of controlled trials and consensus conference. Plast Reconstr Surg. 2016;137:709–730.
2. Sackett DL, Straus SE, Richardson WS, et al. Therapy. In: Evidence-Based Medicine. 2000:2nd ed. Toronto: Churchill Livingstone; 105–153.
3. Swanson E. The case against chemoprophylaxis for venous thromboembolism prevention and the rationale for SAFE anesthesia. Plast Reconstr Surg Glob Open 2014;2:e160.
4. 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.
5. Murphy RX Jr, Alderman A, Gutowski K, et al. Evidence-based practices for thromboembolism prevention: Summary of the ASPS Venous Thromboembolism Task Force Report. Plast Reconstr Surg. 2012;130:168e–175e.
6. 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.
7. Bahl V, Shuman AG, Hu HM, et al. Chemoprophylaxis for venous thromboembolism in otolaryngology. JAMA Otolaryngol Head Neck Surg. 2014;140:999–1005.
8. Bahl V, Hu HM, Henke PK, Wakefield TW, Campbell DA Jr, Caprini JA. A validation study of a retrospective venous thromboembolism risk scoring method. Ann Surg. 2010;251:344–350.
9. Pannucci CJ, Bailey SH, Dreszer G, et al. Validation of the Caprini risk assessment model in plastic and reconstructive surgery patients. J Am Coll Surg. 2011;212:105–112.
10. Shaikh MA, Jeong HS, Mastro A, Davis K, Lysikowski J, Kenkel JM. Analysis of the American Society of Anesthesiologists physical status classification system and Caprini risk assessment model in predicting venous thromboembolic outcomes in plastic surgery patients. Aesthet Surg J. 2016;36:497–505.
11. 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.
12. Swanson E. Caprini scores, risk stratification, and rivaroxaban (Xarelto) in plastic surgery: Time to reconsider our strategy. Plast Reconstr Surg Glob Open 2016;4:e733.
13. Pannucci CJ, Wachtman CF, Dreszer G, et al. The effect of postoperative enoxaparin on risk for reoperative hematoma. Plast Reconstr Surg. 2012;129:160–168.
14. Durnig P, Jungwirth W. Low-molecular-weight heparin and postoperative bleeding in rhytidectomy. Plast Reconstr Surg. 2006;118:502–507; discussion 508.
15. Hatef DA, Kenkel JM, Nguyen MQ, et al. Thromboembolic risk assessment and the efficacy of enoxaparin prophylaxis in excisional body contouring surgery. Plast Reconstr Surg. 2008;122:269–279.
16. Dini GM, Ferreira MC, Albuquerque LG, Ferreira LM. How safe is thromboprophylaxis in abdominoplasty? Plast Reconstr Surg. 2012;130:851e–857e.
17. Patronella CK. Redefining abdominal anatomy: 10 key elements for restoring form in abdominoplasty. Aesthet Surg J. 2015;35:972–986.
18. McDevitt NB. Deep vein thrombosis prophylaxis: American Society of Plastic and Reconstructive Surgeons. Plast Reconstr Surg. 1999;104:1923–1928.
19. Urbankova J, Quiroz R, Kucher N, Goldhaber SZ. Intermittent pneumatic compression and deep vein thrombosis prevention: A meta-analysis in postoperative patients. Thromb Haemost. 2005;94:1181–1185.
20. Swanson E. Do sequential compression devices really reduce the risk of venous thromboembolism in plastic surgery patients? Plast Reconstr Surg. 2015;136:577e–578e.
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