ClinicalClinical FeaturesHaematology

Hospital-Acquired-Thrombosis (HAT) Kills – how we should we protect against it?

Authors: Dr Katie Liston and Dr Ciara O’Rafferty, Department of Haematology, Tallaght University Hospital, Dublin

The epidemiology and relevance of Hospital-Acquired Thrombosis (HAT)

Venous thromboembolism (VTE) is defined as the development of a blood clot within the venous system. These blood clots commonly arise within the deep veins of the leg, known as a deep vein thrombosis (DVT). Clots formed in this area have the potential to migrate to the vasculature of the lung, known as a pulmonary embolus (PE). In situ pulmonary thrombosis also occurs, particularly with Covid-19 infection. PE is associated with significant morbidity and mortality. Large PEs can lead to hypoxia, right heart strain, arrhythmia, systemic shock and death. The HSE estimated that VTE affected 6,772 patients in acute public hospitals in Ireland in 2021. VTE is a causative factor in 10% of deaths.

Hospital-acquired thrombosis (HAT) refers to VTE that occurs during hospitalisation or in the 90 days post-discharge. Hospitalisation is one of the leading risk factors for VTE. This is partly due to the close relationship that exists between inflammation and activation of the coagulation cascade. Hospitalised patients are more likely to have multiple acquired risk factors for VTE such as immobilisation, dehydration, malignancy, infection and surgery. Epidemiological studies have shown that before the use of thromboprophylaxis in hospital, up to 60% of all VTE events were hospital-acquired.

HAT is one of the leading causes of preventable hospital acquired death. In a major study sponsored by the World Health Organization, HAT accounted for more deaths and disability than nosocomial pneumonia, catheter-related bloodstream infections, or adverse drug events in low and middle income countries. HAT is potentially preventable in 65% of cases through the use of appropriate thromboprophylaxis methods.

How can HAT be prevented?

There are various methods of pharmacological and non-pharmacological VTE prophylaxis. General measures that should be considered in all patients include adequate hydration, maintaining mobility, especially post-operatively and the avoidance of the combined oral contraceptive pill or HRT, where appropriate. Anti embolic stockings are a method of mechanical prophylaxis in widespread use throughout Irish hospitals. They are fitted compression stockings that introduce a pressure gradient from ankle to calf working against venous stasis and clot formation, although evidence to support their use is limited. Intermittent pneumatic compression devices can also be used for mechanical prophylaxis.

Pharmacological VTE prophylaxis is the most effective method of reducing VTE events in hospitalised patients. LMWH is the agent of choice in most international guidelines for most patient cohorts. The benefits of LMWH include its short duration of action, partial reversibility, a good safety profile and the extensive published and unpublished experience with its use. Direct oral anticoagulants may be used more extensively in the future for prophylaxis, but evidence to support their net benefit in the majority of patients is currently lacking. The patient’s weight and renal function must be taken into account when calculating the correct dose of LMWH prophylaxis. Evidence supports the use of higher dose LMWH as thromboprophylaxis in the setting of moderate Covid-19 infection.

However, patients vary in their risk of thrombosis and their risk of bleeding so the universal prescription of VTE prophylaxis may result in harm. Individual risk assessment for thrombosis and bleeding is considered to be the standard of care on admission to hospital. Prophylaxis should be administered according to a decision support tool. As hospital admissions are dynamic, the risk balance may change over time, so that patients may require further risk assessments when their clinical circumstances change.

In recent years, more recognition has been given to the need for a systematic and coordinated approach towards the prevention of HAT both across national healthcare systems and also across individual hospitals. Whilst healthcare staff may be aware of the prophylactic modalities available to their patients, they may not have the resources to implement risk assessment and prophylaxis. Care pathways may not facilitate VTE risk assessment. Variation in education and seniority also exists between clinicians. It is therefore important for a hospital/healthcare system to have a VTE prevention protocol. Such a protocol should combine international evidence and local knowledge of patient pathways and practice. Each hospital should have a VTE prevention committee to provide governance for protocol development. Some preventative strategies have proven more effective than others. For example, having a dedicated pre-printed thromboprophylaxis prescription in the drug chart has been shown to increase compliance with VTE prevention protocols. Key performance indicator data should be collected and audited.

In 2012, in the UK, the National Institute for Clinical Excellence (NICE) published a guideline on VTE prevention and this was rolled out across all UK hospitals, with the help of financial incentives to encourage compliance. Such incentives allowed hospitals to develop an infrastructure for a VTE prevention protocol. Data from the implementation of this programme showed that hospitals that achieved risk-assessment targets had a reduced mortality from PE in both inpatients and also in the 90 days post discharge. This was demonstrable in both medical and surgical patients. NICE have also published data to show that VTE prophylaxis is cost effective.

In 2018, the HSE carried out a quality improvement project and have subsequently published recommendations based on this project. Having an adequately resourced VTE prevention team, a VTE prevention committee and a clinically accessible VTE prevention protocol as well as individual risk assessment for every patient are the cornerstones of these recommendations, as is regular data collection and auditing. Patient advocacy now plays a large role in the driving of change and healthcare policy. The importance of educating the patient about the risk factors for VTE, the signs and symptoms of a clot and the role they can take themselves post discharge to reduce their personal risk of clot has become more widely recognised. The need to routinely deliver education to each patient and the need to audit this parameter are key areas highlighted in the HSE recommendations.

The Challenges of rolling out a hospital-wide VTE prevention programme

Whilst HSE recommendations provide useful standards and advice for hospitals trying to implement their own VTE prevention programme, they are somewhat idealised, in that adequate resourcing of such a programme is assumed. Irish hospitals have struggled to get funding for VTE prevention nurses, pharmacists and consultant posts. Staff shortages amongst non-consultant hospital doctors and nursing staff mean that priority has to be placed on dealing with emergent situations with preventative medicine often coming in second place. Furthermore, many different VTE risk assessment tools exist, none of which has been shown to be

superior. Prescribing algorithms and recommendations differ between international guidelines mainly due to gaps in the evidence base and varying interpretations of evidence, making institutional consensus on the best approach difficult to achieve. As a VTE prevention programme has far reaching implications for nearly every clinical staff member and patient, multiple stakeholder involvement in the drafting of a VTE protocol is essential, but not always easy. Complex system change is always difficult to implement, with unforeseen setbacks occurring.

In spite of the challenges in implementing such a programme, the clear need for a hospital wide VTE prevention strategy is unquestionable. Routine risk assessment for VTE and thrombosis should be implemented as standard of care in all hospitals, but the required staff supports for this are crucial. There is an impetus on all clinical staff and hospital managers to support a VTE prevention programme in order to achieve best outcomes for patients.

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