Surgical Thromboprophylaxis

Surgery activates clotting and immobilises the patient, so the risk of postoperative venous thromboembolism depends on the operation, the patient and the expected recovery. Prophylaxis combines early mobilisation, mechanical measures and, for most moderate to high-risk operations, anticoagulant drugs started around the time of surgery.

Risk by operation. Highest risk: major orthopaedic surgery (hip and knee replacement, hip fracture), major abdominal and pelvic cancer surgery, neurosurgery, spinal surgery with immobility, and major trauma. Low risk: day-case surgery with early mobilisation.

Patient factors. Prior thrombosis, cancer, obesity, age over 60 years, oestrogen therapy, varicose veins with phlebitis and prolonged operations over 90 minutes.

• General and gynaecological surgery at moderate or high risk: enoxaparin 40 mg subcutaneously once daily, started 6 to 12 hours after surgery or 12 hours before it. Unfractionated heparin 5000 units every 8 to 12 hours is an alternative.
• Major cancer surgery (abdominal or pelvic): enoxaparin 40 mg daily for 28 days.
• Hip replacement: enoxaparin 40 mg daily for 28 to 35 days; or rivaroxaban 10 mg daily for 35 days; or apixaban 2.5 mg twice daily for 32 to 38 days; or dabigatran 110 mg on the first day then 220 mg daily for 28 to 35 days.
• Knee replacement: enoxaparin 40 mg daily for 10 to 14 days; or rivaroxaban 10 mg daily for 14 days; or apixaban 2.5 mg twice daily for 10 to 14 days. Low-dose aspirin 75 to 150 mg daily is an accepted alternative after an initial 5 to 14 days of low molecular weight heparin in low-risk patients.
• Hip fracture: enoxaparin 40 mg daily, started on admission and continued for 28 to 35 days. Omit the dose 12 hours before surgery.
• Mechanical: intermittent pneumatic compression for all patients at high risk or when drugs are contraindicated.

Neuraxial anaesthesia. Give low molecular weight heparin at least 12 hours before puncture and 4 hours after catheter removal. Direct oral anticoagulants: wait at least 6 hours after catheter removal for the first dose.

Kidney impairment. Reduce enoxaparin to 20 mg daily at creatinine clearance 15 to 30 mL/min. Avoid rivaroxaban and apixaban below 15 mL/min and dabigatran below 30 mL/min.

Obesity. Body mass index 40 or over: enoxaparin 40 mg twice daily.

Low body weight. Under 50 kg: enoxaparin 20 mg daily.

Previous bleeding or very high bleeding risk. Use mechanical prophylaxis alone until bleeding risk falls.

Special groups. Pregnant patients undergoing surgery or caesarean section have weight-banded low molecular weight heparin. In East Africa, trauma and orthopaedic patients with delayed presentation and long traction periods have high risk, and limited stocks make unfractionated heparin an acceptable choice.

Monitoring. Check wound and drain bleeding daily, full blood count every 2 to 3 days for 14 days, and creatinine at baseline and weekly.

Referral and escalation. Seek specialist review for bleeding at the operation site, platelet fall over 50%, or suspected pulmonary embolism, and before any neuraxial block in a patient on prophylaxis.

Stopping. Stop at the end of the planned duration, or when the patient is fully mobile and the surgical wound is healed, whichever is later in high-risk surgery.