Venous thromboembolism — deep vein thrombosis and pulmonary embolism — is one of the commonest preventable causes of death after surgery. Prevention has three parts: assess the risk, assess the bleeding risk, and prescribe the right prophylaxis for the right length of time.
Two kinds of score
| Risk scores | Diagnostic scores | |
|---|---|---|
| Question | How likely is this patient to develop a clot? | Does this patient have a clot now? |
| When | Before surgery and on admission | When a DVT or PE is suspected |
| Examples | Caprini (surgical patients); Padua (medical patients); the UK national VTE risk-assessment tool | Wells DVT, Wells PE, PERC rule, Geneva score |
| Leads to | A prophylaxis plan | D-dimer, ultrasound or CT pulmonary angiogram |
Why surgical patients clot: Virchow’s triad
Step 1: assess the VTE risk with the Caprini score
The Caprini score adds points for the patient (age, cancer, previous VTE, thrombophilia, obesity) and for the operation (minor, major, laparoscopic over 45 minutes, joint replacement). Score your patient here.
| Caprini | Risk group | Expected VTE risk without prophylaxis | Prophylaxis (general and abdominal surgery) |
|---|---|---|---|
| 0 | Very low | Under 0.5% | Early mobilisation only |
| 1–2 | Low | About 1.5% | Mechanical, preferably intermittent pneumatic compression |
| 3–4 | Moderate | About 3% | Low-molecular-weight heparin (LMWH) or low-dose unfractionated heparin; mechanical if the bleeding risk is high |
| 5 or more | High | About 6% | LMWH plus mechanical prophylaxis. Extended LMWH for 4 weeks after abdominal or pelvic cancer surgery |
Step 2: assess the bleeding risk
Prophylaxis is a balance. Before prescribing heparin, look for:
- Active bleeding, or a bleeding disorder such as haemophilia
- Platelets below 75 × 109/L
- Uncontrolled hypertension (230/120 mmHg or more)
- Acute stroke, or neurosurgery, spinal or eye surgery
- An epidural or spinal: time the heparin dose around the insertion and removal of the catheter
- Severe kidney impairment: the LMWH dose may need reducing
If the bleeding risk is high, use mechanical prophylaxis and start heparin once it falls.
Step 3: choose the prophylaxis
| Method | Points to know |
|---|---|
| Early mobilisation and hydration | For every patient. The cheapest prophylaxis there is. |
| Intermittent pneumatic compression | Squeezes the calves in theatre and on the ward. Avoid on a leg with a wound, ulcer or severe peripheral arterial disease. |
| Anti-embolism stockings | Measure for the correct size. Not for patients with peripheral arterial disease, neuropathy or fragile skin, or after a stroke. |
| Low-molecular-weight heparin | For example enoxaparin 40 mg once daily subcutaneously, usually from 6–12 hours after surgery. Adjust for kidney function and body weight; higher doses are used in bariatric patients. |
| Unfractionated heparin | 5000 units subcutaneously two or three times daily. Preferred when kidney function is very poor. |
| Direct oral anticoagulants | Licensed for prophylaxis after hip and knee replacement (for example rivaroxaban, apixaban). |
Extended prophylaxis
- Major abdominal or pelvic cancer surgery: LMWH for 28 days after surgery
- Hip replacement: about 28–35 days; knee replacement: about 14 days
- Bariatric surgery: consider extended prophylaxis in the highest-risk patients
Step 4: if a clot is suspected
| Score | Likely | Unlikely |
|---|---|---|
| Wells DVT | 2 or more: leg ultrasound | Below 2: D-dimer, then ultrasound if positive |
| Wells PE | Over 4: CT pulmonary angiogram | 4 or less: D-dimer, then CTPA if positive |
The post-operative trap
The D-dimer is raised in almost every patient after surgery, so a positive result tells you very little. In a post-operative patient with a suspected clot, go straight to imaging. A tachycardic, hypoxic patient a few days after surgery with a clear chest has a PE until proven otherwise — see ABG case 5.
Practise
Sources and local practice
Based on the American College of Chest Physicians guideline for non-orthopaedic surgical patients (Gould et al., 2012), NICE NG89 (venous thromboembolism in over-16s) and NICE NG158 (diagnosis of DVT and PE). Drug choice and doses vary between hospitals: follow your local policy.