Section 2: Prophylaxis of Venous Thromboembolism (VTE) with Low Molecular Weight Heparin (LMWH)

This guideline will provide general guidance for thromboprophylaxis for adult patients in the medical and surgical setting with LMWH.

This guideline does NOT apply to obstetrics patients. For specialist guidance in this area, please refer to the Royal College of Obstetricians and Gynaecologists (RCOG) Green Top guidance.

Unit-specific guidance may be in place in certain departments and should be used in preference to this generic guidance in the relevant units.

This guideline also does NOT apply to paediatric patients.

Thromboprophylaxis

General guidance

An individual risk assessment for VTE should be carried out for all acutely ill patients within 24 hours of admission or by the first consultant review, whichever is first. Patients should be reassessed every 48 hours or when the clinical situation changes. In each case, consider thrombosis risk and bleeding risk. Enoxaparin is licensed for up to 14 days when used for thromboprophylaxis, all patients prescribed enoxaparin should have this reviewed after 14 days and a decision made to stop or continue if the patient remains at high risk of VTE. Indication to continue after 14 days should be clearly documented.

Patients who are already on therapeutic anticoagulation with LMWH, UFH, DOACs, or Vitamin K antagonists (with a therapeutic INR) do not require further thromboprophylaxis.

Where bleeding risk outweighs thrombosis risk, pharmacological thromboprophylaxis should be withheld and mechanical thromboprophylaxis should be prescribed instead, provided it is not contraindicated. This decision should be reviewed daily, with pharmacological thromboprophylaxis commenced when bleeding risk subsides.

Pharmacological thromboprophylaxis and/or mechanical thromboprophylaxis should be prescribed in the patient’s Kardex.

All decisions regarding use of thromboprophylaxis, including its omission, should be clearly documented in the clinical notes.

All patients receiving LMWH should have a baseline platelet count. Most patients will not require routine monitoring – see Section 4 Unfractionated Heparin (UFH) and heparin-induced thrombocytopenia (HIT): Platelet count monitoring in patients receiving heparins for information on patient groups requiring further platelet monitoring.

VTE and bleeding risk assessment

This should be completed on page 1 of the patient’s Kardex – “VTE Risk Assessment”

Consider VTE risk factors. These should be reassessed every 48 hours or when the patient’s clinical condition changes:

Table 1 – VTE risk factors

Age >60	Acute surgical admission with inflammatory or intra-abdominal conditions	ITU admission
Dehydration	Varicose veins	Lower limb fracture
Known thrombophilia	Immobility, plaster cast, active paralysis	Recent surgery/ anaesthetic > 45mins, or recent hospitalisation
Obesity with BMI > 30 kg/m²	Use of hormone replacement therapy, oestrogen containing contraception, tamoxifen	Active cancer or cancer treatment
Previous history or first degree relative with VTE	Haematological disorder: myeloproliferative disease, paraproteinaemia, behcet’s disease, haemolytic anaemias	≥ 1 significant medical co-morbidities (e.g. cardiovascular disease, diabetes)
Hip or knee replacement	Sepsis/severe infection	Pregnancy or ≤ 6 weeks post-partum

Consider bleeding risk. This should be reassessed every 48 hours or when the patient’s clinical condition changes:

Table 2 – Bleeding risk factors

Thrombocytopenia (platelets < 50 x 10⁹/L)	Known or suspected bleeding	Concurrent use of anticoagulants (with INR > 2 in the case of VKAs)
Uncontrolled severe hypertension with BP > 230/120mmHg	Peptic ulcer	Severe hepatic disease / coagulopathy (PT > 18s)
Recent neuro, spinal, thyroid, or eye surgery (within 1 month)	Acute stroke / Acute/recent cerebral haemorrhage	Untreated inherited bleeding disorder (e.g. von Willebrand)
Invasive procedure (e.g. lumbar puncture / spinal/epidural anaesthesia / organ biopsy) in the next 12 hours or in the previous 4 hours	Planned operation within 6 hours or recent procedure with high bleeding risk	Cerebral metastases
Pregnant: likely delivery in next 24 hours	Active bacterial endocarditis	HIT (Heparin-induced thrombocytopenia)

Consider specific contraindications to thromboprophylaxis with enoxaparin on admission or when the patient’s clinical situation changes. If any of the below factors are present and pharmacological thromboprophylaxis is indicated, discuss with haematology team:

History of heparin-induced thrombocytopenia (HIT)
Allergy to Enoxaparin or other LMWH

VTE prophylaxis with LMWH

Medical patients

Medical patients with low thrombosis risk, defined as no presence of VTE risk factors as detailed in Table 1, do not routinely require mechanical or pharmacological thromboprophylaxis. VTE and bleeding risk should be reviewed at point of admission, then every 48 hours or when the patient’s clinical situation changes.

Patients with high thrombosis risk, as defined by the presence of one or more risk factors as detailed in Table 1, should receive pharmacological thromboprophylaxis, provided that there are no risk factors for bleeding – see dosing table.

Surgical patients

The decision to prescribe thromboprophylaxis for surgical patients should be based on both their VTE and bleeding risk (per tables 1 and 2) as well as their surgical procedure, where applicable.

Table 3: Thromboprophylaxis for surgical patients

Low thrombosis risk

(Minor surgery < 45 mins with no risk factors)

Mobilise early, no mechanical or pharmacological thromboprophylaxis required. Review VTE and bleeding risk in 24 hours.

Moderate risk

(Minor surgery < 45 mins with ≥ 1 risk factors OR major surgery with no risk factors)

Thromboprophylaxis indicated. Prescribe enoxaparin, provided no contraindications. See dosing table

VTE prophylaxis should continue for at least 5-7 days post-procedure or until patient is fully mobile.

High thrombosis risk

(Major surgery with ≥ 1 risk factors)

Thromboprophylaxis indicated. Prescribe enoxaparin, provided no contraindications. See dosing table

VTE prophylaxis should continue for at least 7-10 days post-procedure regardless of mobility. In some cases, extended VTE prophylaxis may be considered on surgeon’s advice.

Dosing table

Enoxaparin is the LMWH of choice in NHS Borders. Patients should be weighed (kg) during admission and the weight should be documented in the patient’s notes within the “Multidisciplinary Assessment & Communication” booklet. Enoxaparin is administered as a subcutaneous (s/c) injection and comes in a 20mg, 40mg, 60mg, 80mg, 100mg, 120mg, and 150mg pre-filled syringe (PFS).

The following table provides recommended doses of enoxaparin for thromboprophylaxis including dose adjustments for extremes of body weight and renal impairment. Each patient should be considered on an individual basis for VTE and bleeding risk and discussed as necessary.

Due to limited clinical evidence for prophylactic LWMH in extremes of body weight and renal impairment, all doses recommended are ‘off-label’. Monitoring of LMWH assay is recommended (*) only for patients with a body weight >150kg, see section for LMWH level monitoring.

For patients with an acute kidney injury (AKI), ensure the renal function is reviewed regularly and adjust enoxaparin dose as recovery of renal function occurs. Where available, calculated creatinine clearance (CrCl) should be used in preference over eGFR. Where this is unavailable, dose based on the patient’s eGFR results.

Table 4: Enoxaparin dosing table for thromboprophylaxis

Weight (kg)	Dosage in eGFR ≥30ml/min/1.73m²	Dosage in eGFR 15-29 ml/min/1.73m²	Dosage in eGFR <15 ml/min/1.73m² (including intermittent HD and CVVHD)
<50kg	20mg ONCE daily	20mg ONCE daily	For low to moderate thrombosis risk consider mechanical measures. 20mg ONCE daily
50-100kg	40mg ONCE daily	20mg ONCE daily	For low to moderate thrombosis risk consider mechanical measures. 20mg ONCE daily
101-150kg	40mg TWICE daily	40mg ONCE daily	40mg ONCE daily
>150kg	60mg TWICE daily*	40mg TWICE daily*	40mg ONCE daily*

VTE prophylaxis with contraindications to LMWH

For all patients where thromboprophylaxis is indicated but there is a specific contraindication to enoxaparin, consider mechanical thromboprophylaxis.

Medical patients with raised bleeding risk

Low thrombosis risk	Mobilise early, no mechanical or pharmacological thromboprophylaxis required. Review VTE and bleeding risk in 24 hours.
High thrombosis risk	Senior clinician to assess relative risks and benefits of pharmacological thromboprophylaxis. If contraindicated, use mechanical thromboprophylaxis.

Surgical patients with raised bleeding risk

Low thrombosis risk

(Minor surgery <30mins with no risk factors)

Mobilise early, no mechanical or pharmacological thromboprophylaxis required. Review VTE and bleeding risk in 24 hours.

Moderate risk

(Minor surgery <30mins with ≥ 1 risk factors OR major surgery with no risk factors)

Use mechanical thromboprophylaxis, mobilise early and ensure adequate hydration.

High thrombosis risk

(Major surgery with ≥ 1 risk factors)

Senior clinician to assess relative risks and benefits of pharmacological thromboprophylaxis. If contraindicated, use mechanical thromboprophylaxis.

Mechanical thromboprophylaxis

Thrombo-embolus Deterrent Stockings (TEDS) are the most commonly used form of mechanical thromboprophylaxis. For particularly high thrombosis risk cases, if the use of prophylactic LMWH is contraindicated, the use of intermittent pneumatic compression (IPC) device (Flowtron) may be used instead for increased efficacy.

The correct size TEDS should be used. Incorrectly fitted TEDS can cause skin damage. Calf-length TEDS may be used where thigh-length TEDS are unsuitable. TEDS should be removed for 30 minutes for each 24-hour period.

TEDS or IPC should be prescribed on the patient’s Kardex.

Reassess daily for any changes to skin or changes to patient condition such as oedema. Re-measure if required in view of any significant changes in clinical condition. Mechanical thromboprophylaxis can be continued throughout the duration of the admission or until patient has returned to pre-admission mobility.

Table 5: Contraindications to TEDS

Severe peripheral arterial disease

Peripheral neuropathy of legs

Leg and/or foot ulcers

Fragile skin or skin allergy to TEDS

Major limb deformity

Severe leg oedema

Cellulitis or dermatitis

LMWH Assay Monitoring (Anti Factor-Xa Monitoring)

Sampling

LMWH assay sampling is time dependent. The peak level sample must be taken 3 to 4 hours after the LMWH dose has been administered.

Order “Anti-Xa assay” (this will also appear if searching “LMWH assay”) on TrakCare – there is no need to contact Haematology when requesting this.

Target peak level

The target peak range for thromboprophylaxis is 0.1-0.4 units/ml. If level is within the appropriate range then no further sampling is required, unless there are any signs of bleeding or bruising. If level is out with intended range, consider discussion with Haematology or Pharmacy for further advice.

VTE Prophylaxis with LMWH and Epidural Catheters

There should be at a gap of at least 12 hours after the last prophylactic dose of LMWH and at least 4 hours before the next prophylactic dose of LMWH when epidural catheters are inserted or removed. This applies for both ONCE daily and TWICE daily dosing.