Venous thromboembolism, including both pulmonary embolism and deep vein thrombosis (DVT), is a major cause of morbidity and mortality in patients undergoing surgery.1–3 In a pooled analysis of patients who underwent gynecologic surgery without venous thromboembolism prophylaxis, the reported rates of DVT ranged from 4% to 38% with an average of 16%.4 Fatal pulmonary emboli occur in 0.4% of patients.4 In addition to the substantial resource use for patients who develop a venous thromboembolism, patients with nonfatal thromboemboli are at risk for recurrent DVT or pulmonary embolus and postthrombotic syndrome. A number of risk factors, including advanced age, prior venous thromboembolism, cancer, and pelvic radiation, increase the risk of venous thromboembolism in patients undergoing gynecologic surgery.1,2,4
Given the catastrophic effects of perioperative thromboembolic disease, there is a strong rationale for prevention. A series of studies have suggested that venous thromboembolism prophylaxis is highly effective in the prevention of venous thromboembolism.1,2,4 For patients undergoing gynecologic surgery, both mechanical and pharmacologic methods of prophylaxis have been shown to effectively reduce the incidence of perioperative venous thromboembolism.5–10 In addition, a number of studies have shown that clinically meaningful bleeding with prophylactic doses of anticoagulation is uncommon.1
Given the abundance of data, a number of professional societies have developed evidence-based guidelines to facilitate appropriate thromboprophylaxis. The American College of Chest Physicians now recommends that all women who undergo major gynecologic surgery receive prophylaxis with unfractionated heparin, low molecular weight heparin, or intermittent pneumatic compression devices.1 The American College of Obstetricians and Gynecologists recommends unfractionated heparin, low molecular weight heparin, or pneumatic compression devices for patients at moderate or high risk who undergo gynecologic surgery. Graduated compression stockings are an alternative for moderate-risk patients.3
Despite the widespread availability of thromboprophylaxis guidelines, little is known about compliance with the recommendations in patients who undergo gynecologic surgery in the United States. For other surgical specialties, a number of studies have reported that the use of perioperative venous thromboembolism prophylaxis is poor.11–13 We performed an analysis to estimate the use of venous thromboembolism prophylaxis in women who underwent abdominal and vaginal surgery for benign disease and to estimate the patient, physician, and hospital characteristics associated with appropriate prophylaxis.
MATERIALS AND METHODS
The Perspective database was used. Perspective is a nationwide, voluntary, fee-supported database developed to measure quality, outcomes, and resource use. The database includes more than 500 acute-care hospitals located throughout the United States that contribute data on inpatient hospital admissions. Each participating institution submits electronic updates on a quarterly basis. The data are audited regularly to ensure quality and integrity. Perspective captures data on patient demographics, disease characteristics, procedures, and all billed services. As such, the database contains information on all drugs, devices, radiologic tests, laboratory tests, and therapeutic services rendered during a patient's hospital course. Perspective is validated and has been used in a number of outcomes studies.11,14–16 The study was approved by the Columbia University Institutional Review Board.
Patients who underwent gynecologic surgery for benign disease between 2000 and 2010 were analyzed. We selected patients who underwent the following procedures: abdominal hysterectomy (International Classification of Diseases, 9th Revision [ICD-9] 68.3, 68.39, 68.4, 68.9), vaginal hysterectomy (ICD-9 68.5, 68.59), salpingo-oophorectomy or cystectomy (ICD-9 65.22, 65.29, 65.3, 65.39, 65.4, 65.49, 65.5, 65.51, 65.52, 65.6, 65.61, 65.62), or colporrhaphy (ICD-9 70.5X). These procedures categories were not mutually exclusive and patients may have undergone multiple procedures. Patients who underwent a primary laparoscopic procedure were excluded. Patients with a diagnosis of cancer of the genitourinary tract were excluded and reported in a separate analysis.
Demographic data analyzed included age (younger than 40, 41–65 compared with older than 65 years of age), race (white, African American, other), year of diagnosis (2000–2003, 2004–2007 compared with 2008–2010), primary payer (Medicare, Medicaid, commercial insurance, uninsured), marital status (married compared with single), and length of stay (less than 3 days, 3–7 days, more than 7 days). Comorbidity was estimated using the Charlson index. The ICD-9 coding for calculation of the Charlson index was based on the classification system developed by Deyo and colleagues.17
Systems characteristics analyzed included geographic area (midwest, northeast, south, west), hospital location (urban compared with rural), hospital teaching status (teaching compared with nonteaching), and hospital size (less than 400, 400–600, greater than 600 beds). Annualized procedural volume was calculated to explore the effect of physician and hospital case volume on the use of prophylaxis. Each hospital or surgeon's annual case volume was estimated by dividing the number of patients who underwent surgery by the number of years an individual hospital or surgeon performed at least one procedure. The distribution of annual surgical volume was inspected visually and cut points selected to create tertiles of surgeon and hospital volume, each with similar numbers of patients; low-volume, intermediate-volume, and high-volume as has been reported in prior work.18,19
Each patient was classified based on the type of venous thromboembolism prophylaxis they received. Patients who had either graduated compression stockings or intermittent pneumatic compression devices were coded as mechanical prophylaxis. Patients who received unfractionated heparin, low molecular weight heparin (including enoxaparin sodium, tinzaparin sodium, or dalteparin sodium), or fondaparinux sodium were classified as having received pharmacologic prophylaxis. Patients who received mechanical prophylaxis in combination with pharmacologic prophylaxis were coded as having received combination prophylaxis.20 Two separate end points were analyzed. Any prophylaxis was defined as having received mechanical, pharmacologic, or combination prophylaxis. A second analysis was performed to specifically examine use of pharmacologic prophylaxis, which may consist of either pharmacologic prophylaxis alone or combination prophylaxis.
The association between patient, physician, and hospital characteristics and use of prophylaxis was examined using χ2 tests. Multivariable logistic regression models were developed to determine the use of prophylaxis while controlling for other patient, physician, and hospital characteristics. Separate models were developed to examine use of any prophylaxis and use of pharmacologic prophylaxis. P<.05 was considered statistically significant. All analyses were performed with SAS 9.2.
A total of 738,150 patients were identified. No venous thromboembolism prophylaxis was given to 292,034 (39.6%) women, whereas 344,068 (46.6%) had mechanical prophylaxis, 40,268 (5.5%) received pharmacologic prophylaxis, and 61,780 (8.4%) received combination (pharmacologic and mechanical) prophylaxis (Table 1). In a univariable analysis, patient characteristics associated with use of prophylaxis included older age, insurance coverage with Medicare, treatment more recently, hospitalization for more than 7 days, residence in the southern or midwestern United States, and greater medical comorbidity (P<.05 for all). Patients treated at rural hospitals, teaching facilities, and intermediate- and large-volume hospitals were more likely to receive prophylaxis (P<.05 for all). Among women treated at low-volume hospitals, 60.8% received prophylaxis compared with 59.4% of patients at high-volume hospitals (P<.001). Low-volume physicians administered venous thromboembolism prophylaxis in 58.2% of their cases, whereas high-volume physicians used prophylaxis in 63.5% of their patients (P<.001).
Figure 1 displays the use of prophylaxis based on the year of diagnosis. In 2000, 46.5% of patients received no prophylaxis. By 2010, 32.5% of patients did not receive any form of prophylaxis. Use of mechanical prophylaxis was 44.0% in 2000, peaked at 49.8% in 2006, and then decreased to 43.0% by 2010. Pharmacologic prophylaxis increased from 3.4% to 10.3% during the study period, whereas combination prophylaxis rose from 6.1% in 2000 to 14.2% in 2010.
Table 2 displays a multivariable logistic regression model of factors associated with any prophylaxis. Women older than 65 years of age (odds ratio [OR] 1.51, 95% confidence interval [CI] 1.47–1.55), those with Medicare (OR 1.12, 95% CI 1.09–1.14), patients with more than two comorbid conditions (OR 1.46, 95% CI 1.42–1.50), and those diagnosed from 2008 to 2010 (OR 1.81, 95% CI 1.79–1.84) were more likely to receive some form of prophylaxis, whereas African American women (OR 0.90, 95% CI 0.88–0.91) and single patients (OR 0.97, 95% CI 0.96–0.99) were less likely to receive prophylaxis. Patients treated at rural hospitals (OR 1.21, 95% CI 1.19–1.23), teaching hospitals (OR 1.03, 95% CI 1.02–1.05), and intermediate-sized facilities (OR 1.26, 95% CI 1.24–1.28) were more likely to receive prophylaxis, whereas patients in the northeast (OR 0.70, 95% CI 0.68–0.71) and west (OR 0.61, 95% CI 0.60–0.62) were less likely to receive prophylaxis. Patients treated by high-volume physicians (OR 1.02, 95% CI 1.00–1.03) and high-volume hospitals (OR 1.25, 95% CI 1.23–1.27) more often received some form of prophylaxis.
Factors associated with use of pharmacologic prophylaxis included advanced age (older than 65 years), white race, noncommercial insurance (Medicare, Medicaid, uninsured), later year of diagnosis, hospital stay more than 7 days, treatment in the northeast, and greater comorbidity (P<.05 for all) (Table 2). Patients treated at rural hospitals (OR 0.95, 95% CI 0.93–0.97) were less likely to receive pharmacologic prophylaxis, whereas women operated on at teaching hospitals (OR 1.34, 95% CI 1.32–1.37) and larger facilities (OR 1.08, 95% CI 1.06–1.11) more often received pharmacologic prophylaxis. Although women treated by high-volume surgeons more often received pharmacologic prophylaxis (OR 1.47, 95% CI 1.44–1.49), high hospital volume (OR 0.97, 95% CI 0.95–0.99) was associated with a lower rate of pharmacologic venous thromboembolism prophylaxis.
Given the importance of physician and hospital volume on prophylaxis, we performed an analysis stratified by year of diagnosis and surgical volume. The use of any prophylaxis increased from 48.0% to 61.1% at low-volume hospitals and from 53.7%–77.1% at high-volume facilities through the study. In 2000, 49.5% of patients treated by low-volume physicians and 57.4% treated by high-volume surgeons had prophylaxis. By 2010, this increased to 64.9% and 71.0%, respectively (Fig. 2). Pharmacologic prophylaxis increased from 12.4% to 21.8% at low-volume hospitals and from 7.3% to 27.5% at high-volume hospitals over time. Pharmacologic prophylaxis by low-volume physicians increased from 10.1% to 25.5% and from 9.8% to 25.0% for high-volume surgeons (Fig. 3).
Despite clear recommendations from evidence-based guidelines, our findings suggest that venous thromboembolism prophylaxis is underused in women undergoing abdominal and vaginal surgery for benign disease. Even in 2010, nearly one-third of women did not receive any form of prophylaxis. Encouragingly, use of prophylaxis, particularly pharmacologic prophylaxis, increased with time.
A number of studies have reported that compliance with venous thromboembolism prophylaxis is poor.11–13,16,21–24 The multinational venous thromboembolism risk and prophylaxis in the acute hospital care setting (Epidemiologic International Day for the Evaluation of Patients at Risk for Venous Thromboembolism in the Acute Hospital Care Setting [ENDORSE]) study examined over 68,000 patients from 32 countries. The investigators noted that only 59% of surgical patients and 40% of at-risk medical patients received some form of prophylaxis.12 When adherence to specific guideline-based recommendations for the appropriate timing and type of prophylaxis is examined, compliance is even lower.16,24 Administration of the appropriate type of venous thromboembolism prophylaxis preoperatively and for 24 hours after surgery as recommended by the US Surgical Care Improvement Project was noted in only 53% of patients in one analysis.24
The type of procedure performed appears to be the most important determinant of whether venous thromboembolism prophylaxis is used.12,13,16,21–23 Although data are limited, compliance with prophylaxis appears to be lower in gynecologic surgery than other high-risk specialties.13 One study reported that 54% of patients undergoing gynecologic or urologic procedures received prophylaxis compared with 86% for orthopedic procedures and 67% for abdominal and vascular surgery.13 In addition to the type of procedure performed, a multitude of other patient-related factors, including age, race, comorbidity, prior thromboembolic disease, and the presence of cancer, also appears to influence the use of prophylaxis.12,13,16,21–23 We noted that patients at higher risk for venous thromboembolism, older women and those with medical comorbidities, were more likely to receive prophylaxis, whereas African American women were 10% less likely than their white counterparts to receive prophylaxis.
Physician and hospital factors also had a strong influence on the allocation of prophylaxis. Patients treated by high-volume physicians, at rural hospitals, teaching hospitals, midsized facilities, and high-volume centers were more likely to receive some form of prophylaxis. Pharmacologic prophylaxis was more commonly given to patients at urban hospitals, teaching facilities, large hospitals, and to patients treated by high-volume surgeons. There is increasing recognition that in addition to patient characteristics, physician and systems factors play an important role in the care patients receive.25–27
Surgical volume was highly associated with use of prophylaxis. For many procedures, surgical volume has a strong influence on outcome.28,29 Although the volume–outcome paradigm is well described, the factors that underlie this finding remain poorly defined.15,18,19,30–33 Although higher volume may result in improved technical skill and better operative decision-making, volume is a surrogate for the entire process of care that a patient receives from the preoperative period through discharge. Improved perioperative care through adherence to evidence-based recommendations may be one of the factors contributing to the effect of volume on outcome. Our group previously demonstrated that for patients undergoing oncologic surgery, those patients treated by high-volume hospitals and surgeons were more likely to receive perioperative venous thromboembolism prophylaxis.34 In contrast, other studies examining the association between volume and guideline adherence have found only week associations.15,30–32
Our findings were interesting in that hospital volume appeared to be a driving factor in receipt of any prophylaxis, but physician volume seemed to have a greater influence on use of pharmacologic prophylaxis. One potential explanation for these findings is that hospital protocols influence overall use of prophylaxis but the specific choice to use pharmacologic prophylaxis rests with physicians. Further work to examine how physician characteristics influence the allocation of venous thromboembolism prophylaxis is clearly needed.
Although our study benefits from the inclusion of a large cohort of patients, we recognize a number of important limitations. Because the primary purpose of claims data is for billing, we cannot exclude the possibility that venous thromboembolism prophylaxis was misclassified in some patients. Because the Perspective database has been validated in a number of studies that have examined drug and device use, the number of patients misclassified is likely small.11,15,16,30 Among patients who developed a venous thromboembolism, it is difficult to determine if prophylactic anticoagulation was administered before the event or if only therapeutic anticoagulation was given after the diagnosis of the thromboembolism. Given the large sample, the proportion of patients misclassified is likely to be small. Although we were able to estimate the number of patients who received venous thromboembolism prophylaxis, it is not possible to examine the quality of prophylaxis. First, it is well known the compliance with mechanical prophylaxis among patients is poor.35 Second, although we reported the use of pharmacologic prophylaxis, this certainly does not ensure that the proper dose of the drug was administered throughout the hospitalization. In our analysis, we did not attempt to separate patients with contraindications to pharmacologic prophylaxis given that they would have been candidates for mechanical prophylaxis. Given the large number of patients, hospitals, and procedures in our analysis, it was difficult to correct for all possible clustering. It should be recognized that some studies in gynecologic surgery have reported that pharmacologic prophylaxis is associated with an increased risk of bleeding.7 Our study included a large sample size and it must be recognized that although some findings may have been statistically significant, they may not be clinically meaningful. Finally, although our data represent a sample from over 500 hospitals, our findings may not be generalizable to all hospitals and providers.
Our findings are concerning in that 40% of patients failed to receive prophylaxis. Although the use of prophylaxis increased, even in 2010, nearly one-third of women did not receive prophylaxis. The importance of venous thromboembolism prophylaxis has now gained increased recognition by both patients and payers. The Centers for Medicare and Medicaid Services now recognize DVT and pulmonary embolus after orthopedic procedures as a hospital-acquired condition and as such, its occurrence results in decreased reimbursement. To increase physician, hospital, and patient awareness, venous thromboembolism is now often used as a surrogate for quality. Venous thromboembolism rates are frequently publicly reported and prophylaxis is a common initiative used in pay-for-performance programs.36,37 There has also been a strong emphasis on more formalized venous thromboembolism prophylaxis protocols. The latest iteration of the American College of Chest Physicians thromboprophylaxis guidelines specifically calls for institution-wide thromboprophylaxis policies as well as strategies to increase adherence such as computerized decision systems, preprinted orders, and audits and feedback.1 Given the morbidity associated with venous thromboembolism as well as the fact events are highly preventable, our findings highlight the urgent need for further interventions to improve prophylaxis in women undergoing gynecologic surgery.
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© 2011 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
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