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This guide provides an approach to performing a venous thromboembolism (VTE) risk assessment, including management and documentation, to prescribe pharmacological and mechanical thromboprophylaxis (prevention of thrombus formation).
A VTE risk assessment should be carried out on admission and 24 hours post-admission for every patient. There may be variations in VTE risk assessment and thromboprophylaxis measures used, so local guidance should always be followed.
Background
VTE refers to a thrombus (stationary blood clot forming within a vessel) developing in the venous system, which can dislodge and become an embolus in the pulmonary vasculature. This is commonly known as a deep vein thrombosis (DVT), causing a pulmonary embolus (PE), both of which should be prevented and treated promptly upon diagnosis.
Patients with reduced mobility during admission have an increased risk of developing VTE after 24 hours, and for up to 90 days after discharge.1 Preventing VTE reduces mortality rates from PE, long-term complications and healthcare costs, therefore, it is a vital assessment to perform.2
Introduction
To perform a VTE risk assessment, you will require the patient’s medical history, medication history (including allergies), family history, examination findings, observations, and investigations (such as blood tests and relevant imaging reports).
This guide uses the Department of Health’s VTE risk assessment tool, as recommended by NICE.3
Risk assessment
To determine whether thromboprophylaxis treatment should be initiated for a patient, there are three key steps in the risk assessment process. These are to:
1. Determine the level of mobility at the point of admission: this determines whether or not to continue the risk assessment.
2. Identify thrombosis and bleeding risk factors.
3. Determine if both pharmacological and mechanical thromboprophylaxis are suitable, considering the balance of risk factors, and then prescribe the appropriate treatments.
Patient mobility
The more immobile a patient is during admission, the higher the risk of developing VTE. Mobility is divided into the following:
- Surgical patient: including elective and emergency admissions, who will be immobile throughout most of their admission, either due to a surgical condition or due to the surgery itself
- Medical patient expected to have ongoing reduced mobility: including those bedbound, unable to walk unaided or spending most of their day in a bed or chair for at least 3 days
- Medical patient not expected to have reduced mobility compared to their normal state: e.g. most psychiatric inpatients3-5
All surgical patients or those with reduced mobility should undergo further assessment of thrombosis and bleeding risk. Where a medical patient is not expected to have reduced mobility, the risk assessment is complete, and no further prophylaxis is currently indicated.
A patient’s mobility and clinical situation can change throughout the course of their hospital admission. Therefore, it is crucial to reassess VTE risk regularly.
Thrombosis risk factors
This section involves reviewing thrombosis risk factors, which are divided into patient and admission related, and increase the risk of clot formation.3
Patient related factors
These are either due to a medical condition, non-modifiable risk factors, hormonal treatments or pregnancy:
- Active cancer or cancer treatment
- Age > 60
- Dehydration
- Known thrombophilia
- Obesity (BMI >30kg/m2)
- One or more significant medical comorbidities (e.g. heart disease; metabolic, endocrine or respiratory pathologies; acute infectious diseases; inflammatory conditions)
- Personal history or first-degree relative with a history of VTE
- Use of hormone replacement therapy
- Use of oestrogen-containing contraceptive therapy
- Varicose veins with phlebitis
- Pregnancy or < 6 weeks post-partum
Thromboprophylaxis in pregnancy
Although pregnancy and the post-partum period, up to 6 weeks, are risk factors for thrombus formation, it is always important to consult local guidance or the Royal College of Obstetricians and Gynaecologists, as they may have a different risk assessment tool and prescribing policy.
Admission related factors
These are attributed to a surgical procedure, an immobilising surgical condition, critical care or a combination of these:
- Significantly reduced mobility for 3 days or more
- Hip or knee replacement
- Hip fracture
- Total anaesthetic + surgical time > 90 minutes
- Surgery involving pelvis or lower limb with total anaesthetic + surgical time > 60 minutes
- Acute surgical admission with inflammatory or intra-abdominal condition
- Critical care admission
- Surgery with significant reduction in mobility
Different surgical specialities will have their own criteria regarding the type of thromboprophylaxis, when to initiate it and its duration. Therefore, it is essential to consult the specialist team and local guidelines first before prescribing thromboprophylaxis.
Bleeding risk factors
This section involves reviewing bleeding risk factors, which are divided into patient and admission related.3
Patient related factors
These are due to clinical states, medical conditions or pre-existing anticoagulation:
- Active bleeding
- Acquired bleeding disorder (e.g. acute liver failure)
- Concurrent use of anticoagulants known to increase the risk of bleeding (e.g. warfarin with INR >2)
- Acute stroke
- Thrombocytopaenia (platelets <75 x 109/L)
- Uncontrolled systolic hypertension (230/120 mmHg or higher)
- Untreated inherited bleeding disorders (e.g. haemophilia and von Willebrand’s disease)
Admission related factors
These include procedures where increased bleeding may be expected during or after, and would lead to an adverse effect on the patient:
- Neurosurgery, spinal or eye surgery
- Other procedures with high bleeding risk
- Lumbar puncture/epidural/spinal anaesthesia expected within the next 12 hours
- Lumbar puncture/epidural/spinal anaesthesia within the previous 4 hours
Management
Most patients will be suitable to receive both pharmacological and mechanical thromboprophylaxis, however, others may be suitable for one of these, or none, depending on the outcome of the risk assessment.
The decision to initiate thromboprophylaxis rests on the balance of thrombosis and bleeding risk factors.
If there are only thrombosis risk factors, pharmacological thromboprophylaxis should be prescribed.
If there are thrombosis risk factors and one or more bleeding risk factors, a senior discussion is required before prescribing pharmacological prophylaxis to evaluate the risk of VTE against the risk of bleeding. It may prompt further discussion with other specialities, such as haematology or the surgical team, to arrive at an individualised plan.
Communicating thromboprophylaxis management
Patients should be informed of their risk of developing VTE and the proposed management plan to reduce this risk. The risks and benefits of any treatment should be clearly explained, including that pharmacological treatment may increase the risk of bleeding.
The discussion should also involve gaining consent for providing treatment.
A patient information leaflet should be offered about VTE risk and thromboprophylaxis.
Mechanical thromboprophylaxis
Mechanical thromboprophylaxis is a device or garment worn on one or both legs to provide compression and reduce the risk of clot formation by encouraging venous blood flow and return. These can still be prescribed if there is an increased bleeding risk and pharmacological prophylaxis is not contraindicated.
The two main forms of mechanical thromboprophylaxis include:
- Intermittent pneumatic compression (IPC): electrical devices that wrap around the calf or foot and mimic their muscles and venous blood flow in a cyclical deflating and inflating fashion, while applying pressure
- TED stockings: also known as thromboembolic deterrents or graduated compression stockings. These are tight, elastic garments worn over the foot that apply graduated pressure to the ankle and calf to encourage venous return
Factors that help determine which one to use include the patient’s comorbidities, reason for admission, contraindications, availability, and ultimately, local hospital policy.
Contraindications
Mechanical thromboprophylaxis is contraindicated in those with peripheral vascular disease, severe lower limb neuropathy, allergy to stockings and lower limb cellulitis. However, this list is non-exhaustive, and each type has its own set of contraindications.
Pharmacological thromboprophylaxis
Pharmacological thromboprophylaxis is anticoagulant medication that reduces the risk of blood clotting through chemical means. You should always follow local guidelines on thromboprophylaxis prescribing, but subcutaneous administration of heparins is commonly used:
- Low molecular weight heparin (LMWH) (e.g. enoxaparin and dalteparin): first-line treatment, with dosage and frequency dependent on the patient’s weight, renal function, and pregnancy status
- Fondaparinux: if LMWH is contraindicated
- Unfractionated heparin (UFH): less commonly used as it requires monitoring APTT and administering two to three times a day
LMWH and UFH products are commonly derived from porcine intestinal mucosa, which may conflict with certain religious beliefs. You should discuss alternative pharmacological thromboprophylaxis (such as fondaparinux), which does not contain animal products, including its suitability, advantages, and disadvantages, with the patient.6 Local guidance should also be consulted.
Pre-existing oral anticoagulation
For patients prescribed oral anticoagulation (e.g. apixaban for atrial fibrillation) whose risk assessment recommends pharmacological thromboprophylaxis, no additional pharmacological thromboprophylaxis is typically required, and the regular oral anticoagulant should be continued. Some risk assessment tools include a section to tick for pre-existing anticoagulation.
Mechanical thromboprophylaxis should still be prescribed alongside if appropriate.
Documentation
VTE risk assessment tool
The VTE risk assessment tool must be completed, including recording the level of mobility, thrombosis, and bleeding risk factors, and determining whether mechanical and/or pharmacological thromboprophylaxis is indicated or contraindicated.
There is also a section to sign and date, indicating that the assessment was completed.
Remember, thromboprophylaxis management may change if the patient’s clinical condition or situation changes during their admission (e.g. if they develop apparent or occult bleeding, or are admitted to critical care), and so regular reassessment and consideration are essential.
Prescription chart
Most hospital prescription charts, whether digital or handwritten, will have a dedicated section for thromboprophylaxis of both types. The prescription chart should clearly state the:
- Medicine/product name
- Date
- Dose
- Route
- Frequency
- Time of administration
- Prescriber’s name, contact number, and signature
Reviewer
Dr Hon-Wing Shek
Acute Medicine Consultant
Editor
Dr Jamie Scriven
References
- Horner D, Goodacre S, Davis S, et al. Which is the best model to assess risk for venous thromboembolism in hospitalised patients? BMJ. 2021. Available from: [LINK].
- Hunt BJ. Preventing hospital associated venous thromboembolism. BMJ. 2019. Available from: [LINK].
- Department of Health. Risk Assessment for Venous Thromboembolism (VTE). 2018. Available from: [LINK].
- Hill J, Treasure T. Reducing the risk of venous thromboembolism in patients admitted to hospital: summary of NICE guidance. BMJ. 2010. Available from: [LINK].
- Ye F, Bell LN, Mazza J, et al. Variation in Definitions of Immobility in Pharmacological Thromboprophylaxis Clinical Trials in Medical Inpatients: A Systematic Review. Clinical and Applied Thrombosis/Haemostasis. 2016. Available from: [LINK].
- NICE NG89. Venous thromboembolism in over 16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism. 2018. Available from: [LINK].
Image references
- Figure 1-3. Department of Health. Risk Assessment for Venous Thromboembolism (VTE). Adapted by Geeky Medics. License: [Open Government Licence v3.0].
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