Thromboprophylaxis for Medical and Surgical Patients

Assessment of VTE and bleeding risk

All patients must have their risk of venous thromboembolism (VTE) assessed at admission (+/- at pre-admission clinic) using the appropriate risk assessment tool and then regularly during their stay in hospital. A record of these assessments must be made (e.g. on the specialty-appropriate Risk Assessment sheet) and documented in the thromboprophylaxis section of the kardex.

Assess the patient within 24 hours of admission using the following flowchart and indicators as guidance and reassess risk of bleeding and VTE within 48-72 hours of admission and regularly thereafter.

Different specialty specific algorithms apply for orthopaedics, ENT and obstetrics.

Further information on assessment:

  • Do not offer pharmacological prophylaxis to patients with risk factors for bleeding shown in table 2 below unless the risk of VTE outweighs the risk of bleeding.
  • Patients already receiving therapeutic anticoagulation do not need additional thromboprophylaxis.

Table 1 – Indicators of patients at increased risk of VTE

Regard medical patients and surgical patients who have not had a surgical procedure as being at increased risk of VTE if they are expected to have ongoing (≥2 days) reduced mobility relative to their normal state and have one or more of the risk factors below. Regard post-operative patients as being at increased risk of VTE if they have one or more of the following risk factors:

  • Acute surgical admission with inflammatory or intra-abdominal condition, including pelvic inflammatory disease
  • Dehydration
  • Critical care admission (e.g. ITU, HDU)
  • Surgical procedure with total anaesthetic/ surgical time >90 minutes, or >60 minutes if surgery on lower limb or pelvis
  • Age >60 years
  • Obesity (BMI >30kg/m2)
  • Active cancer or cancer treatment
  • Known thrombophilia
  • Personal history or 1st degree relative with a history of VTE
  • Hip fracture
  • Current significant medical condition e.g.
    • serious infection
    • heart failure
    • respiratory disease
    • inflammatory disease
  • Pregnancy or ≤6 weeks post partum
  • Hormone replacement therapy or tamoxifen
  • Oestrogen containing contraceptive therapy
  • Varicose veins with phlebitis
  • All gynaecological surgery except uncomplicated gynaecological diagnostic day case procedures

This list is not comprehensive and there will be patients with other specific conditions which are sufficiently pro-thrombotic that merit thromboprophylaxis.

Table 2 – Indicators of patients at high risk of bleeding

Regard patient at risk of bleeding if they have any of the following risk factors:

  • Surgery expected within next 12 hours
  • CrCl <30ml/minute (enoxaparin dose reduction required)
  • Active bleeding or risk of bleeding including:
    • new-onset stroke (within 14 days)
    • platelet count <75 x 109/L
    • liver failure
  • Concurrent use of therapeutic anticoagulant (e.g. warfarin, apixaban, dabigatran, rivaroxaban, edoxaban) is a contra-indication to additional pharmacological thromboprophylaxis
  • Acute bacterial endocarditis
  • Any spinal intervention (prophylactic enoxaparin dose is contraindicated for 12 hours before spinal and epidural anaesthetics and lumbar puncture. Enoxaparin contraindicated for 4 hours after spinal and epidural anaesthetics and removal of epidural catheter)
  • Persistent uncontrolled hypertension (BP ≥230/120mmHg)
  • Untreated inherited bleeding disorder (e.g. haemophilia or von Willebrands)
  • High risk of peri- or post-procedural bleeding (e.g. neurosurgery, spinal, thyroid and posterior eye surgery)
  • Trauma with high bleeding risk (e.g. head injury)

General management and treatment options

  • Surgical patients who merit pharmacological thromboprophylaxis should receive enoxaparin SC 40mg daily (at 6pm) and anti-embolism stockings (AES).
  • Non-operative patients who merit pharmacological thromboprophylaxis should receive enoxaparin SC 40mg daily (at 6pm) only.

If creatinine clearance (CrCl) <30ml/minute, see below, under Renal Impairment, for guidance.

Enoxaparin should only be prescribed after assessing the risks of VTE and balancing against the risks of bleeding. Contraindications should be considered carefully (e.g. Heparin-induced Thrombocytopenia (HIT), acute bacterial endocarditis, renal impairment, recent stroke, etc).

Renal impairment

Significant renal impairment (CrCl <30ml/minute) is associated with an increased anticoagulant-related bleeding risk. In some patients the bleeding risk associated with low molecular weight heparin (LMWH) may outweigh the anti-thrombotic benefit, when it would be appropriate to withhold enoxaparin and apply mechanical thromboprophylaxis. If enoxaparin is deemed appropriate then see here for dose reduction. 

Extremes of weight

In low weight patients (<50kg) reduce the dose to enoxaparin SC 20mg daily. Extremely heavy patients (>120kg), with normal renal function, may merit a higher dose; enoxaparin 40mg SC twice daily especially if multiple thrombotic risk factors are present. For more information see the full GGC guideline Heparin Dose Adjustment, Adult Patients with Very High, or Low Body Weight.

Timing of enoxaparin administration

For medical in-patients enoxaparin should be prescribed at 6pm. For surgical in-patients with a significant reduction in mobility, enoxaparin should be prescribed at 6pm the night before surgery, otherwise it should be started after surgery at the later of: 4 hours post-operatively or 6pm. Then at 6pm on subsequent days.

Same day admission and day surgery

Compared to inpatient surgery, day case surgery generally confers a lower (but not zero) VTE risk. Therefore these patients should be similarly risk assessed for VTE and bleeding risk, and if appropriate anti-embolism stockings (AES) and LMWH prescribed. In patients perceived to be at very high VTE risk, consideration can be given to extending LMWH prophylaxis post discharge.

For patients admitted on the day of surgery who require enoxaparin thromboprophylaxis:

  • AES at admission
  • Enoxaparin started after surgery at the later of: 4 hours post-operatively or 6pm. Then at 6pm on subsequent days.

Precautions with epidural and spinal anaesthetic techniques

Epidural and spinal anaesthetic techniques should not be carried out within 12 hours of a prophylactic dose of enoxaparin. Likewise epidural catheters should not be removed within 12 hours of a prophylactic dose of enoxaparin. Wait >4 hours after any of these procedures before giving next dose of enoxaparin. In most cases, administration of enoxaparin at 6pm will avoid any difficulties here.

Monitoring platelet count

All patients prescribed heparin, including LMWH, should have a baseline platelet count assessed. Heparin-induced thrombocytopenia (HIT) is most commonly seen in post-operative patients receiving unfractionated heparin (UFH). Post-operative patients receiving UFH and post cardio-pulmonary bypass (CPB) patients receiving UFH or LMWH should have platelet count monitoring every 2–3 days from days 4 to 14 or until heparin is stopped. If the platelet count falls to <100 x109/L, or if there is a smaller but significant drop (30–50%) from baseline, stop the heparin and seek specialist advice. Medical and obstetric patients receiving UFH or LMWH, and post-operative patients (excluding post-CPB patients) receiving LMWH, have a low risk of HIT and do not require routine platelet count monitoring for this purpose. Further advice on the diagnosis and treatment of HIT can be found here.

Mechanical thromboprophylaxis

Anti-embolism stockings (AES) are the most commonly used form of mechanical thromboprophylaxis. However, for particularly high thrombosis-risk patients (e.g. immobile acute stroke patients) while LMWH is contraindicated, the use of intermittent pneumatic compression (IPC) devices can provide superior efficacy. There is a GGC protocol for the use of IPC post stroke and this is available in all the GGC stroke units. IPC have similar contraindications as for AES (see below).

Anti-embolism stockings

  • Sigel profile compliant AES should be used.
  • Calf length AES may be used where thigh length AES are unsuitable.
  • AES may be replaced with intermittent pneumatic compression devices (IPC) whilst in hospital.
  • AES must be removed for 30 minutes in each 24 hour period.
  • Reassess daily for any changes to skin or changes to patient's condition such as oedema, and re-measure if any changes noted.
  • Medical practitioners must prescribe the use of AES within the medication kardex.

Incorrect fitting of AES can be detrimental to the patient causing skin damage. Observation and continual assessment is required.

Do not offer AES to patients who have:
Peripheral arterial disease
Peripheral neuropathy of legs
Leg / foot ulcers
Fragile ‘tissue paper’ skin
Major limb deformity (or unusual size or shape of leg) or skin allergy to AES
Cellulitis or massive oedema
Cautions with AES:
Ensure the correct size is provided
Re-measuring and refitting may be required
Ensure good capillary refill after fitting
Show patients how to use AES
Ensure patients discharged with AES are able to remove and replace them (or have assistance)
Do not fold down the tops of AES

Duration of thromboprophylaxis

  • AES – continue until patient discharged and returned to pre-admission level of mobility.
  • Enoxaparin – usually stopped at discharge, or earlier if patient no longer at high thrombotic risk when re-assessed.
  • Extended anticoagulant thromboprophylaxis is indicated in specific patients (e.g. known high risk thrombophilia or previous post-op VTE, but not on long-term warfarin) or situations (e.g. post abdomino-pelvic cancer surgery, TKR or THR).

General recommendations


Guideline reviewed: February 2021

Page last updated: September 2023