Risk Assessment

All patients admitted to hospital in England should be risk assessed to ascertain their individual risk of thrombosis and bleeding. This vital assessment informs whether thromboprophylaxis is required. The simultaneous assessment of both thrombosis and bleeding allows clinicians to make considered decisions about how best to maintain haemostasis to ensure that patient safety is optimised. This careful balance between bleeding and clotting can fluctuate frequently in acutely unwell patients, emphasising the need for reassessment as clinical condition changes.

Risk assessment is a collaborative process to be performed with the patient. This offers an ideal opportunity to impart information about the risk of VTE as well as signs and symptoms and what action to take should they develop. The National target for VTE risk assessment in England is currently 95% although it is important that organisations aim to risk assess all adult admissions.
The National VTE Prevention Programme

The National VTE Prevention Programme launched in England in 2010. The principal aim was to reduce morbidity and mortality associated with preventable hospital-associated venous thromboembolism (VTE). An innovative, comprehensive and systematic approach was taken underpinned by the introduction of a financially incentivised mandatory, documented VTE risk assessment on admission to hospital (target 90% risk assessment rate at launch; Institute for Innovation and Improvement, 2010). This was supported by thromboprophylaxis guidance published by NICE with a quality standard outlining best practice (NICE 2010a,b). Additional initiatives include the National VTE Exemplar Centre Network, a national VTE prevention website (now decommissioned) and an electronic learning resource for VTE prevention.

VTE risk assessment was introduced as one of three national initiatives in the CQUIN (Commissioning for Quality and Innovation) scheme in 2010 and was novel in that the process applied to every adult patient admitted to an acute hospital (Department of Health, 2009). During the first year of the CQUIN incentive payment, the mean VTE risk assessment improved to more than 91% of all patients admitted to hospital. After 3 years, the target was raised to 95% and continues to be exceeded (96%, March 2017) (Graph 1). VTE prevention remains in the NHS Standard Contract as a quality indicator. Increased expenditure on prophylactic low molecular weight heparin provides indirect evidence for increased uptake of thromboprophylaxis (Roberts et al, 2015). Local evaluations have also demonstrated significant increases in both documented risk assessment and appropriate thromboprophylaxis (Basey et al, 2012; Bateman et al, 2013).

Impact of the National Programme

There are two published studies examining the national impact of the VTE prevention programme on the incidence and mortality associated with hospital-associated thrombosis (HAT).

Lester et al (2013) report an observational cohort study of all patients admitted to NHS hospitals from July 2010 to March 2012, excluding primary admissions attributed to VTE. Linked hospital episode statistics (HES) and Office of National Statistics (ONS) data was utilised. Hospitals achieving >90% risk assessment had a significant reduction in deaths with VTE as a primary cause of death in the 90 days following both admissions of more than 3 days (RR 0.85, 95% CI 0.75–0.96) and admissions of lesser duration (RR 0.61, 95% CI 0.48–0.79). Catterick et al (2013) utilised the same data sources (HES and ONS) to examine secondary VTE diagnoses, VTE readmissions and mortality from 2006 to 2012. They compared actual mean rates of VTE in 2011/12 to that estimated from linear regression of VTE rates over 2006 to 2010. They observed a 9% reduction in secondary VTE diagnoses, 4% reduction in 90 day readmissions with VTE and 9% reduction in the mean mortality rate in 2011 to that estimated by regression.

The NHS Outcomes Framework includes mortality from VTE within 90 days of hospitalisation and has reported an overall downward trend in mortality with a reduction in crude death rate of 10.8% from 2006 to 2015 (Clinical Indicators Team, NHS Digital, 2017).

The need for thromboprophylaxis in this patient group (particularly in patients being treated conservatively in the outpatient setting) remains a controversial topic. The absolute incidence of symptomatic VTE appears to be low and there is limited evidence to recommend routinely giving thromboprophylaxis. The KAF study (Selby et al, 2014), a multicentre prospective cohort study to define the prevalence of symptomatic VTE in patients with a tibial, fibular, or ankle fracture (treated non-operatively) or a patellar or foot fracture (treated operatively or conservatively)  found the incidence of symptomatic VTE to be 0.6% without thromboprophylaxis.

A Cochrane review (2017) concluded that there is moderate quality evidence to support the use of LMWH in outpatients with lower limb immobilisation (when compared with no prophylaxis or placebo) and despite no significant difference in PE rates between LMWH and control groups (low quality evidence), there were fewer  symptomatic VTEs in the LMWH groups.

This was based on a meta-analysis and the eight studies included differed widely in many respects e.g. different types and doses of LMWH, different risk groups (e.g. non-operative, operative) as well as primary outcomes (e.g. symptomatic vs asymptomatic DVT).

More recent data suggests that LMWH given throughout the period of immobilisation may not be effective for the prevention of symptomatic VTE (POT-CAST trial, van Andrichem et al, 2017). Notably, although patients managed both conservatively and surgically were included in this trial, patients with a history of VTE were excluded, as were pregnant patients and those with multiple traumatic injuries.

The latest NICE guidelines (NG98 2018) state:

“Consider pharmacological VTE prophylaxis with LMWH or fondaparinux sodium for people with lower limb immobilisation whose risk of VTE outweighs their risk of bleeding. Consider stopping prophylaxis if lower limb immobilisation continues beyond 42 days.”

Practice varies widely across the UK and many different risk assessment tools are in use at various hospitals. NICE guidelines (NG98 2018) recommend that risk assessment should be performed “using a tool published by a national UK body, professional network or peer-reviewed journal”. Importantly, there is no validated risk assessment tool for this patient group.

In summary, patients deemed to be high risk of VTE should be considered for thromboprophylaxis during lower-limb immobilisation but the question of how this group should be defined remains unresolved.

VTE risk assessment for all pregnant women should occur in early pregnancy and then again in labour or immediately after delivery. Some women deemed to be at high thrombotic risk may require thromboprophylaxis throughout pregnancy and for 6 weeks post-partum. The Royal College of Obstetricians and Gynaecologists (2015) provides guidance for clinicians in reducing the risk of venous thrombosis in pregnancy and the puerperium.

  The Royal College of Obstetricians and Gynaecologists

Some cancers and cancer treatments are associated with an increased risk of thrombosis. Patients should be risk assessed and considered for thromboprophylaxis in line with NICE (2018) guidance.