Chapter 2. Lay Out the Evidence and Identify Best Practices

Preventing Hospital-Acquired Venous Thromboembolism

Know What the Literature Says

The team will need to rely on at least one content expert who is fluent with the evidence base and best practices for preventing hospital-acquired venous thromboembolism (VTE). Especially relevant and authoritative are the published performance measures from The Joint Commission and guidelines from the American College of Chest Physicians (ACCP) Conference on Antithrombotic and Thrombolytic Therapy.10 These should be supplemented, as needed, with the reading list in the "Literature Review" section of the Society of Hospital Medicine's VTE Quality Improvement Resource Room, which is available at

At least three central realities emerge from the current VTE prevention literature, each with important implications for the team.

Reality 1. While the number and type of VTE risk factors appear to influence a patient's overall VTE risk, there is no validated method to predict accurately or efficiently an individual patient's risk for VTE.

Meanwhile, in the absence of prophylaxis, the risk of VTE across almost all populations of hospitalized patients is significant, as shown in Table 2.

Table 2. Risk of Deep Vein Thrombosis in Hospitalized Patients

No prophylaxis + routine objective screening for DVT

Patient GroupDVT Incidence (%)
Medical patients10-26
Major gynecological, urological, or general surgery15–40
Hip or knee surgery40-60
Major trauma40-80
Spinal cord injury60-80
Critical care patients15-80

The 2004 ACCP conference statement supports a group-specific approach to prophylaxis. Its reasons for this approach are:

  • The inability to confidently identify patients who do not require prophylaxis.
  • The inability to predict how risk factors combine to position an individual patient along the spectrum of thromboembolic risk.
  • The fact that individualizing prophylaxis is logistically complex and likely associated with suboptimal compliance.

Constructing simple risk assessment models that stratify all patients into three to four easy-to understand groups, as opposed to complicated point-scoring systems, is preferable. The concept of the VTE protocol and suggestions for keeping it simple and effective are discussed below and in Chapter 5.

Reality 2. Instances of clear superiority or inferiority do exist among prophylaxis options but for just a few patient groups.

One of the team's fundamental duties is to come up with a way to recommend—as well as judge—the appropriateness of one prophylaxis option over another. For this reason, the second thing to know about the VTE literature is where clear evidence exists to recommend a particular method of prophylaxis over others. The team should know that the most appropriate choice of VTE prophylaxis depends on the patient group and circumstances of the hospital stay.

  • In medical patients, fondaparinux and the low-molecular-weight heparins (LMWHs) enoxaparin and dalteparin have efficacy comparable to heparin given three times a day subcutaneously but offer lower complication rates and other advantages potentially important to patients and nursing staff.18-21
  • In certain higher-risk patient groups (e.g., hip and knee replacement, trauma, and spinal cord injury) LMWH has demonstrated superiority over subcutaneous heparin.10, 22-25
  • In certain patient groups (e.g., hip replacement, surgery for cancer, and possibly medical patients with reduced mobility), extending prophylaxis with LMWH to approximately 5 weeks is more effective than providing it for 1 week.10, 26
  • In certain patient groups, such as medical inpatients, the adequacy of heparin given twice a day subcutaneously has not been proven. High quality randomized trials showing relative equivalence of LMWH to unfractionated heparin (UFH) all used a 5,000-unit, three times a day dosing of UFH.
  • In very high-risk patient groups, the addition of mechanical prophylaxis to a pharmacologic regimen may offer an added benefit.
  • Certain patient groups should not receive certain pharmacologic agents or doses or should receive smaller doses of LMWH (e.g., creatinine clearance less than 30 cc per minute).
  • Certain patient groups should receive pharmacologic doses in close coordination with other events (e.g., surgery or neuroaxial blockade) or with special knowledge by involved physicians (e.g., spine surgeons).

Reality 3. In the quality improvement (QI) literature, no strategy has yet been described for getting the right prophylaxis to the right patient at sustainable and acceptable rates in a way that can be readily replicated by other institutions.

The typical successful strategy described in the literature profiles excellent use of special local resources but with limited transferability. Electronic alerts have raised the prevalence of VTE prophylaxis but in an academic setting with computerized physician order entry (CPOE), electronic decision support, and a high baseline prevalence of VTE prophylaxis.27 In another academic setting, a monthly division-director-led audit and feedback of physician performance was combined successfully with monthly educational offerings for patients the medicine house staff cared for.28 Replicating such strategies in nonteaching or non-CPOE settings would not be possible. More generally, because QI study designs tend not to confirm sustainability or reproducibility, the ability to articulate or judge discrete underlying mechanisms is limited.

At this stage, familiarity with the evidence base positions the team to draft a "VTE protocol," the document that becomes the foundation for the rest of the effort to prevent hospital-acquired VTE, from interventions through performance tracking.

The key concept with a protocol is routine. Doing a complex activity the same way each time is the best way to make sure that nothing is left out. In the hospital, protocols serve that purpose. They standardize and structure the care a group of providers deliver. Routine is important because across a population of patients, provider inconsistency is one of the most common sources of suboptimal care. For a variety of reasons, providers inevitably vary care, whether compared to each other or compared to themselves. In fact, a graph that depicts improved system performance over time almost always shows a progressive narrowing of the range of performance. In a powerful way, protocols have the capacity to improve care by reducing unnecessary variation in performance from medical decisionmaking to ordering.

The best protocols preserve the ability to customize care for special patient situations or circumstances. In contrast to variation arising from provider behavior, variation from the protocol that arises due to special patient situations is always acceptable. The protocol should make that clear.

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Construct the Venous Thromboembolism Protocol

The VTE protocol accomplishes several purposes at once. First, if it is well integrated into all admission, transfer, or post-operative orders, it prompts providers to do the right thing at the right time. Second, it gives providers the option of using, or not using, the decision-support elements. Third, the VTE protocol is a definition of what the team will consider "appropriate prophylaxis" for the patients within the scope of the improvement effort. This definition will be critical when it comes time to measure baseline and new prevalence of appropriate VTE prophylaxis.

The team must focus time and attention on drafting and field-testing the VTE protocol, which is useful as an educational tool and helps set expectations for care. QI intervention principles the team should consider when constructing and evaluating the VTE protocol are discussed in Chapter 5.

The ideal VTE protocol:

  • Is applicable across all patients in the scope. The optimal approach is to have the team create a single VTE protocol for all patient groups targeted by the improvement effort. For example, if the scope includes all medical and surgical patients, the team should avoid customizing separate VTE protocols for general surgery, gynecology, oncology, orthopedic surgery, and medical patients. It should instead try to construct a single VTE protocol that can be applied to all patients. The advantage of this approach comes from the power of standardization.

    A universal VTE protocol:

    – Can be more readily approved and initiated.
    – Is more likely to be recognized as definitive in its authority.
    – Is easier to modify based on feedback.

    Adherence to a single VTE protocol can readily serve as a surrogate measure for performance tracking. The predictable disadvantages are those that come from any effort that tries to apply a common solution to different groups. The challenge is to strike a balance between limiting prophylaxis options too much and allowing for many options. There are several ways to overcome these disadvantages, but the simplest rule of thumb is always to allow providers the leeway of going "off protocol" when clinically appropriate.

  • Is easy to access and easy to use. Simpler is better. Eventually the team may ask providers to refer to or recall elements of the VTE protocol several times during a patient's admission. One of the great determinants of the VTE protocol's success will be whether the team can make its use so easy and automatic that all patients coming into the hospital at any time from any place will be funneled through it.
  • Links each level of risk to evidence-based choices for prevention.
  • Lists contraindications to prophylaxis and encourages reasonable alternatives.

The VTE protocol consists of a standardized VTE risk assessment, a linked menu of appropriate prophylaxis options, and contraindications to pharmacologic or heparin prophylaxis. A sample VTE protocol is included at Appendix B.

Standardized VTE Risk Assessment. A standardized VTE risk assessment delivers decision support to the point of care. In other words, at the moment of medical decisionmaking, providers have what they need to stratify the patient to a specific VTE risk level. No single VTE risk assessment has been prospectively validated as superior to others. Many factors should be taken into account when adapting one. A list of published articles focusing on VTE risk factors and risk assessment appears in Appendix C.


Linked Menu of Appropriate Prophylaxis Options. This menu allows providers to choose the right VTE prophylaxis by "backing into" the choice from the VTE risk level that is derived from the standardized VTE risk assessment. The team must explore local factors that may play a role in selecting agents of choice for each level of VTE risk. The team must account for these local factors when drafting the VTE protocol. Case Studies 1 and 2 showcase how the University of California, San Diego Medical Center and Emory University Hospitals handled common VTE protocol questions.

The team must investigate not only which options are most appropriate for each level of risk but also which agents, given local factors, should be the preferred agents for each level of risk. Relative efficacy, dosing schedules, formulary costs, and side-effect profiles are all important considerations.

The steps to define appropriate prophylaxis are:

  1. Create or adapt any VTE risk assessment to meet local needs.
  2. Choose recommended options for each level of VTE risk.
  3. Decide upon acceptable options for each level of VTE risk. The term "acceptable" is intentionally looser than "recommended" and will become significant when measuring whether prophylaxis is appropriate. For example, while intravenous heparin may not be recommended for VTE prophylaxis, it probably should be considered an acceptable alternative when it is being used for other indications.
  4. Identify absolute and relative contraindications to pharmacologic prophylaxis and settle on acceptable alternatives for these patients.

Contraindications to pharmacologic or heparin prophylaxis. Like the VTE risk assessment, this feature of the VTE protocol delivers decision support to the point of care so that providers know when to choose alternative prophylaxis (i.e., if specific contraindications to anticoagulation or heparin products exist). The team should be wary of being too liberal in defining contraindications to pharmacologic prophylaxis. Many patients with relative contraindications develop VTE and end up on full dose anticoagulation. The team should be as specific as possible when using time parameters. For example, "recent gastrointestinal hemorrhage" is not as useful as "gastrointestinal hemorrhage within 1 month."

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Integrate the Venous Thromboembolism Protocol

The power of the VTE protocol will be unleashed only when it is well integrated into the clinical workflow. This integration will be the team's next objective. How the team accomplishes this will depend on institutional culture and infrastructure, such as whether the hospital uses CPOE or paper order sets.

A recommended approach is to ask a focus group of hospitalists, residents, or anyone who frequently writes admission orders to try out early drafts of the VTE protocol. It is never too early to start listening to the end user. Whatever is learned from focus groups should be incorporated immediately into a new version. Using qualitative feedback to make daily revisions for a week can bring the team very close to perfecting the usability of the VTE protocol. Chapter 4 provides more detail on how to get the most out of early pilot efforts.

Ultimately the team should strive for perfect integration of the VTE protocol into admission and transfer order writing; thus the importance of an easy-to-use model cannot be overstated. Even if the VTE protocol is supremely easy to use, it will be ineffective if patients bypass the protocol. A number of approaches to prevent this outcome, and other methods of enhancing the reliability of the VTE protocol are outlined in the coming chapters.

Current as of August 2008
Internet Citation: Chapter 2. Lay Out the Evidence and Identify Best Practices: Preventing Hospital-Acquired Venous Thromboembolism. August 2008. Agency for Healthcare Research and Quality, Rockville, MD.