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Missed Opportunities for Prevention of Venous Thromboembolism^*

An Evaluation of the Use of Thromboprophylaxis Guidelines

^* From the Department of Medicine (Dr. Arnold) and the Center for Clinical Epidemiology and Community Studies (Drs. Kahn and Shrier), Sir Mortimer B. Davis Jewish General Hospital, Montreal, Canada.

Correspondence to: Susan R. Kahn, MD, MSc, Center for Clinical Epidemiology and Community Studies, Sir Mortimer B. Davis Jewish General Hospital, 3755 Cote Ste, Catherine Rd, Room A-118.1, Montreal, Quebec, Canada, H3T 1E2; e-mail: susank{at}epid.jgh.mcgill.ca

	Abstract

TOP Abstract Introduction Materials and Methods Results Discussion References

 
Objectives: To identify and characterize cases of potentially preventable venous thromboembolism (VTE): cases for which thromboprophylaxis was indicated, according to the American College of Chest Physicians (ACCP) consensus guidelines for VTE prevention, yet was administered inadequately.

Design: A historical cohort study to examine all cases of deep vein thrombosis and pulmonary embolism from 1996 to 1997 at a large teaching hospital. Of these, we determined the proportion that was potentially preventable. We examined the reasons for inadequacy of prophylaxis and the setting in which preventable VTE occurred.

Results: Of 253 objectively diagnosed cases of VTE in 245 patients, 44 cases (17.4%) were considered potentially preventable. This represented two thirds of all VTE cases for which thromboprophylaxis had been indicated (n = 65). Of preventable cases, the most frequent reason for inadequacy of prophylaxis was omission of prophylaxis (47.7%), followed by inadequate duration of prophylaxis (22.7%), and by incorrect type of prophylaxis (20.5%). Surgical and medical indications for thromboprophylaxis that were common among preventable cases included nonorthopedic surgery, admission to hospital for pneumonia, and stroke with lower limb paralysis. Underlying risk factors for VTE that were common among preventable cases included recent immobility, active cancer, and obesity.

Conclusions: One of six cases of all VTE and two of three cases of VTE for which thromboprophylaxis had been indicated could potentially have been prevented had physicians followed the recommended ACCP guidelines. Inadequacy of prophylaxis was most often caused by omission of prophylaxis. Missed opportunities for prevention occurred most commonly in the settings of nonorthopedic surgery, pneumonia, and stroke.

Key Words: guideline implementation • prevention • thromboprophylaxis • venous thromboembolism

	Introduction

TOP Abstract Introduction Materials and Methods Results Discussion References

 
Venous thromboembolism (VTE) is a major cause of morbidity and mortality in hospitalized patients. It is estimated that > 250,000 patients are hospitalized annually in the United States with VTE¹ , and the overall crude mortality rate from pulmonary embolism (PE) at 3 months has been reported to be as high as 17.4%.² Given that deep vein thrombosis (DVT) is often clinically silent and PE may be rapidly fatal, prevention is the most effective strategy to reduce the burden of VTE and has been clearly shown to be cost-effective through a reduction in both fatal complications and treatment requirements.³

Every 3 years since 1986, the American College of Chest Physicians (ACCP) has published comprehensive guidelines for the prevention of VTE, most recently published in January 2001.⁴ The guidelines identify risk groups of patients who should receive thromboprophylaxis, and they recommend the type of prophylaxis that is most appropriate for each risk group. The recommendations are formulated by experts in the field after critical review of the published literature and are categorized on the basis of the strength of the supporting evidence. These evidence-based recommendations are generally considered to be the standard of care for DVT and for PE prevention. However, studies^{2 5 6} suggest that, in practice, implementation of the guidelines may be inconsistent and inadequate.

In this study, we attempted to identify the obstacles that hinder the success of VTE prevention at our institution by examining the rate of preventable VTE during a 1-year time period. Preventable VTE was defined as objectively diagnosed DVT or PE that occurred in a setting in which thromboprophylaxis was indicated but was either administered inadequately or not administered at all. The indications for thromboprophylaxis that were used in this study were outlined in the 1995 ACCP guidelines on VTE prevention,⁷ according to the most recent version of the guidelines available at the time of this study. Among preventable cases of VTE, we examined the reasons for inadequacy of prophylaxis by comparing the prophylaxis regimens used with the prophylaxis regimens recommended by the guidelines. In addition, we compared preventable VTE with nonpreventable VTE, ie, VTE that occurred despite proper adherence to the guidelines, with respect to patient characteristics and the settings in which VTE occurred.

	Materials and Methods

TOP Abstract Introduction Materials and Methods Results Discussion References

 
We conducted a historical cohort study in which we performed a chart review on all patients with objectively diagnosed DVT or PE, who were admitted to the Sir Mortimer B. Davis Jewish General Hospital in Montreal, a 637-bed McGill University teaching hospital, between October 1996 and October 1997. This 1-year period was chosen because (1) it allowed sufficient time for dissemination and implementation of the 1995 ACCP guidelines on VTE prevention,⁷ and (2) it preceded the introduction of an emergency department-based outpatient DVT treatment program, for which recorded clinical information might have been less complete than for VTE patients admitted to hospital. Prior to its initiation, the Research Ethics Committee of the hospital approved the study protocol.

Each episode of VTE was reviewed to determine whether it occurred in a setting in which thromboprophylaxis had been indicated and, if so, whether thromboprophylaxis was adequately administered. To assess indication for and adequacy of thromboprophylaxis, we collected data that allowed us to categorize patients into different risk categories for VTE as specified in the 1995 ACCP guidelines.⁷ Using a standardized data collection form, we abstracted chart data on method of VTE diagnosis, patient characteristics, risk factors for VTE, indications for prophylaxis, and the thromboprophylaxis received. Based on these data, each case of VTE was categorized as preventable, nonpreventable, spontaneous, or ineligible for thromboprophylaxis as detailed below.

VTE Diagnosis
Objective diagnosis of DVT was established by Doppler ultrasonography, compression ultrasonography, venography, or autopsy. A thrombosis was considered proximal if it involved the popliteal vein or any segment proximal to it. The diagnosis of PE was established by ventilation/perfusion scanning read as high probability for PE with a moderate or high clinical suspicion, pulmonary angiography, infused CT, echocardiography, or autopsy.

Patient Characteristics and Risk Factors for VTE
Patient age and gender were recorded. Data on VTE risk factors, as outlined by the ACCP guidelines, were extracted. These included prior DVT or PE; history of cancer and active treatments thereof; use of oral contraceptive pill or hormone replacement therapy; known hypercoagulable state; obesity; varicose veins; fracture of the pelvis, hip, or lower extremity; immobility for at least 3 days before VTE diagnosis; and the presence of an indwelling central venous catheter.

Indications for Thromboprophylaxis
The ACCP guidelines identify clinical events, both surgical and medical, for which prophylactic antithrombotic therapy is indicated. Surgical indications for thromboprophylaxis include elective total hip or total knee arthroplasty, surgical hip fracture repair, general surgery (which comprises vascular, urologic, and cardiac surgical procedures and any orthopedic procedures other than total hip arthroplasty, total knee arthroplasty, and surgery for repair of hip fracture), intracranial neurosurgery, and multiple trauma. General surgical procedures were graded as low risk, moderate risk, high risk, or very high risk based on the patient’s age, the number of risk factors for VTE, and the duration of the surgery, as outlined in the ACCP guidelines.⁷ Medical indications for thromboprophylaxis included admission to the hospital for myocardial infarction, congestive heart failure or chest infection, stroke with lower extremity paralysis, and acute spinal cord injury with paralysis. Data on these clinical events were extracted. If any events occurred during the 6 weeks before VTE diagnosis, we considered them to be possible precipitants of VTE, and prophylaxis was indicated; otherwise, prophylaxis was not indicated.

Adequacy of Thromboprophylaxis
The ACCP guidelines recommend thromboprophylaxis according to risk category. Several acceptable types of prophylaxis are suggested, and the recommended dose, frequency, and duration are specified in the guidelines. To determine the adequacy of thromboprophylaxis, for each case of VTE we compared the actual prophylaxis used with the ACCP guideline recommendations. A priori, thromboprophylaxis was considered adequate if all of the following conditions were met: (1) the prophylaxis used was the same type and at least the same dose and frequency of dosing as that recommended in the guidelines; (2) prophylaxis was administered regularly for at least 7 days, until hospital discharge, or until the patient was ambulatory; and (3) prophylaxis was initiated within 24 h of the precipitating event (eg, surgery, myocardial infarction). Otherwise, thromboprophylaxis was considered inadequate.

Classification of VTE
Based on the above-mentioned data, each case of VTE was categorized as preventable, nonpreventable, spontaneous, or ineligible for our analysis. Preventable cases of VTE were defined as VTE that occurred in a setting in which prophylactic antithrombotic therapy had been indicated but was administered inadequately or omitted. Nonpreventable cases of VTE were those that occurred despite adequate thromboprophylaxis. Spontaneous cases were those cases of VTE that occurred in the absence of a documented indication for thromboprophylaxis. Ineligible cases consisted of cases of VTE that occurred in patients who were ineligible for thromboprophylaxis either because of a contraindication or because the VTE occurred in another institution and the details of the event and of the use of prophylaxis were unavailable.

Analysis
The rate of preventable VTE and the specific reasons for inadequacy of thromboprophylaxis were examined. The clinical characteristics of preventable vs nonpreventable cases were compared using a comparison of simple proportions.

	Results

TOP Abstract Introduction Materials and Methods Results Discussion References

 
During the 1-year study period, 253 cases of acute VTE were objectively diagnosed in 245 patients (Table 1 ). The mean (± SD) age was 70.1 ± 15.5 years, and 57.6% of case subjects were women. There were 48 cases of PE and 230 cases of DVT, most of which were proximal (62.6%) and unilateral (78.7%). Twenty-five patients had both DVT and PE concomitantly. Of the 253 cases of VTE, 44 cases (17.4%) were classified as preventable, 21 cases (8.3%) were nonpreventable, 179 cases (70.8%) were spontaneous, and 9 cases (3.6%) were ineligible for thromboprophylaxis. Therefore, of the 65 cases of VTE for which thromboprophylaxis had been indicated, inadequate prophylaxis was administered in 44 cases (67.7%).

View larger version (28K): [in this window] [in a new window] [Download PPT slide]   Figure 1.. Reasons for inadequacy of prophylaxis in preventable VTE (n = 44).

VTE was suspected in this group of patients after the onset of typical symptoms, and the diagnosis was confirmed by objective testing. Doppler ultrasonography was used to confirm the diagnosis in all but one case of nonpreventable DVT, and compression ultrasonography was used for the remaining case. The one case of PE in this group was confirmed by high-probability ventilation/perfusion lung scan.

	Discussion

TOP Abstract Introduction Materials and Methods Results Discussion References

 
VTE occurs despite adequate thromboprophylaxis at a rate that varies according to the indication for therapy.⁷ Some authors^{2 8} have suggested that the incidence of these breakthrough cases may represent a limitation in efficacy of the recommended guidelines. In our series, if VTE prevention guidelines had been implemented as recommended, then all VTE for which thromboprophylaxis had been indicated should have fallen into the nonpreventable group. We found that only one third of cases (21 of 65 cases) of VTE with a clear indication for prophylaxis were nonpreventable, whereas two thirds of such VTE cases (44 of 65 cases) occurred in the context of inadequate prophylaxis (ie, were potentially preventable). Of all cases of VTE in our series, one sixth of cases (44 of 253 cases) were potentially preventable. These results indicate that there is a need for improvement in thromboprophylaxis implementation.

Our study has attempted to uncover some of the obstacles that may be hindering effective thromboprophylaxis usage. We found that inadequacy of prophylaxis was most often caused by omission of prophylaxis. The reasons for this may include physicians being unaware of the ACCP guideline recommendations, or, in certain clinical situations, physicians forgetting to consider thromboprophylaxis or being deterred by the perceived risk of bleeding.

Missed opportunities for the prevention of VTE occurred most commonly in the settings of general surgery, neurosurgery, pneumonia, and stroke. We hypothesize that the perceived risk of VTE is low for patients undergoing nonorthopedic surgery, despite evidence from pooled data showing that the overall incidence of VTE among general surgical patients is approximately 20%.⁴ Similarly, a low perceived risk of VTE may have contributed to missed opportunities for thromboprophylaxis of patients with pneumonia or stroke in our series, despite current evidence that indicates a 15% incidence of VTE among medical patients.⁹ For patients undergoing neurosurgical procedures and patients with fresh strokes, opportunities for VTE prevention may have been missed because of a perception that the bleeding risk attributable to these patients precluded the use of thromboprophylaxis. There are sufficient data, however, to refute these concerns.^{10 11 12}

There was no obvious gap in VTE prophylaxis for cases occurring in the context of orthopedic surgery, perhaps because the early experience with VTE prophylaxis emerged from this clinical setting and because orthopedic health professionals more routinely implement thromboprophylaxis. Our results show that risk factors more common among patients with preventable VTE included immobility, cancer, and obesity. Physicians may not be taking these clinical characteristics into account when attempting to stratify patients into risk groups for VTE, especially before surgical procedures or during hospital admissions. As a result, adequate thromboprophylaxis may be overlooked.

The cases of DVT or PE in the nonpreventable group occurred despite adequate prophylaxis. This group represents thromboprophylaxis failures and deserves special attention. Nonpreventable VTE occurred most commonly in the setting of orthopedic surgery, despite 7 days of proper prophylaxis with low-molecular-weight heparin, administered in recommended doses. The majority of nonpreventable thromboses were lone distal DVT.

The effectiveness of thromboprophylaxis is known not to be perfect. Goldhaber et al¹³ recently studied a cohort of predominantly medical patients and reported that 52% of patients developed VTE despite antecedent prophylaxis (although the adequacy of the prophylaxis used with respect to the indication is not discussed). The association that we found between high-risk surgical procedures and the occurrence of nonpreventable VTE suggests that the current guidelines for DVT/PE prophylaxis may be inadequate, particularly for those situations that may confer a heightened thrombogenic state. However, the fact that most DVTs that occurred in the nonpreventable group were distal thromboses may imply that the current guidelines for thromboprophylaxis, although not perfectly effective, may be sufficient to prevent the more dangerous proximal DVT and PE.

One nonpreventable case of VTE occurred after only 1 day of thromboprophylaxis. It is possible that VTE was present before the initiation of prophylaxis in that case and would therefore not represent a treatment failure. Nonetheless, the charted information suggested that this was a de novo nonpreventable VTE. Three cases of nonpreventable VTE occurred despite full therapeutic range anticoagulation with either warfarin or full-dose unfractionated heparin therapy. All three cases occurred in the context of a medical admission to hospital, and all three cases were either proximal DVT or PE. Medical patients may be at particularly high risk for VTE because thromboprophylaxis failure occurred despite full anticoagulation and the thromboses that occurred were more serious.

Stratton et al⁵ evaluated the extent of adoption of grade A guideline recommendations in high-risk surgical patients, and found that although 89.3% of patients received some type of thromboprophylaxis, only 63.6% received prophylaxis that conformed to grade A recommendations. Other studies^{2 6 14 15 16 17 18} have examined physician patterns of usage of antithrombotic therapy in general, and most studies^{2 6 14 15 16} concluded that thromboprophylaxis is underused. Three surveys aimed at UK orthopedic surgeons, published between 1989 and 1995,^{14 15 16} showed that 14%, 27.5%, and 25% of respondents, respectively, did not administer any form of thromboprophylaxis after total hip replacement. Thromboprophylaxis usage in the orthopedic setting has since increased. A 1994 survey of 5,000 US orthopedic surgeons concluded that 95% of respondents administered some type of thromboprophylactic therapy for patients undergoing total hip or total knee replacement surgery,¹⁷ and a 1996 chart audit demonstrated that 93% of patients undergoing total hip replacement received some type of prophylaxis.¹⁸ However, in other settings, thromboprophylaxis continues to be underused. A large review⁶ in 1998 of US Medicare patients undergoing major abdominothoracic surgery found that VTE prophylaxis was implemented in only 38% of patients. Analysis of the International Cooperative Pulmonary Embolism Registry,² a registry of 2,454 patients with PE established to identify factors associated with death from PE, concluded that one half of the 708 patients who underwent surgery in the preceding 2 months did not receive perioperative thromboprophylaxis, although the types of surgeries were not specified.

Our study has several limitations. First, because of the historical cohort design, we were not able to directly assess physician practice patterns in the usage of thromboprophylaxis because data on the total number of patients who received prophylaxis were unavailable. Therefore, we do not have the denominator required to determine how consistently clinicians implement the ACCP guidelines and how many VTEs were averted (and therefore excluded from our series) because of proper usage of the guidelines. However, we were able to assess the rate of preventable cases among patients with VTE, and to identify clinical characteristics that were most often associated with preventable VTE. Second, we may have imprecisely estimated the degree of risk of VTE in certain situations. In determining the level of risk (low to very high) for any patient who underwent a general surgical procedure, we adhered strictly to the definitions offered in the ACCP guidelines, which list clinical risk factors for VTE and attribute the same degree of importance to each one. In doing so, the overall risk to a particular patient may be overestimated or underestimated because certain risk factors contribute to a greater extent than others.¹⁹ Third, in assessing whether prophylaxis was adequate or inadequate, we adhered strictly to the definitions outlined in the guidelines. As a result, inadequacy of prophylaxis may have been overestimated because significant clinical differences may not exist for certain aspects of adequate prophylaxis, for example, twice vs three times daily dosing of unfractionated heparin in certain situations. Fourth, clinically manifest VTE was used as our end point and, as such, the rate of VTE in our study population may have been underestimated because it is known that a proportion of DVT and PE are clinically silent.⁷ However, because the ACCP guidelines were developed to reduce the incidence of clinically important thromboembolic disease, we believe that clinically manifest VTE was the appropriate endpoint to use. Finally, we may have underestimated the number of preventable VTE cases because none of the VTE cases that occurred in a setting in which thromboprophylaxis was contraindicated were considered preventable. All contraindications to anticoagulants in our series were attributable to an increased bleeding risk; however, clinical situations in which the bleeding risk becomes prohibitive and thromboprophylaxis is absolutely contraindicated have yet to be clearly defined. As such, omitting thromboprophylaxis in certain situations may not have been justifiable given that the benefit of VTE prevention often outweighs the risk of bleeding.^{10 11 12}

By examining preventable cases of VTE, our study identifies important opportunities for thromboprophylaxis that were missed, including the perioperative period for nonorthopedic surgery and neurosurgery, and the clinical setting of pneumonia, and stroke. Our study also represents a useful mechanism for improving clinical practice with institution-specific data, a method that has been shown to be an effective means of implementing change.^{20 21} Further research should be directed toward determining factors contributing to inadequate thromboprophylaxis and toward improving the process of guideline implementation by practicing physicians, so that appropriate patients can benefit more widely from the available evidence on thromboprophylaxis efficacy.

Finally, although not the primary aim of our study, we have shown, as have others, that even in patients receiving recommended thromboprophylaxis regimens, breakthrough VTE does occur. This highlights the fact that there is still room to improve existing thromboprophylaxis regimens.

	Footnotes

 
Abbreviations: ACCP = American College of Chest Physicians; DVT = deep vein thrombosis; PE = pulmonary embolism; VTE = venous thromboembolism

Drs. Kahn and Shrier are Clinical Research Scholars supported by the Fonds de la Recherche en Santé du Québec, Canada.

Received for publication July 11, 2000. Accepted for publication June 13, 2001.

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