Venous Thromboembolism Prophylaxis in Critical Illness

Most critically ill patients are at high risk of venous thromboembolism and are given pharmacological prophylaxis unless there is a contraindication, with mechanical prophylaxis when drugs are unsafe. The choice of agent depends on kidney function, weight and bleeding risk.

Contraindications. Active bleeding, platelets under 50 x 10^9/L (some practice uses under 30), severe uncorrected coagulopathy, recent intracranial haemorrhage or neurosurgery (delay until a stable scan, usually 24 to 72 hours), and history of heparin-induced thrombocytopenia.

Neuraxial procedures. Give prophylactic enoxaparin at least 12 hours before and at least 4 hours after insertion or removal of an epidural or spinal catheter.

Agent. Enoxaparin or another low-molecular-weight heparin. Use unfractionated heparin when creatinine clearance is under 30 mL/min or procedures are planned.

Mechanical. Intermittent pneumatic compression when anticoagulants are contraindicated, and stop it as soon as drugs can be started.

Special groups.

• Obesity: use the higher dose of 40 mg every 12 hours when weight is over 100 kg.

• Trauma: enoxaparin 30 mg subcutaneously every 12 hours or 40 mg once daily.

• Pregnancy: enoxaparin 40 mg once daily, adjusted for weight at the extremes.

• Children: not routine, with specialist advice.

• East Africa: low-molecular-weight heparin may be unavailable, so use unfractionated heparin and keep records of platelet counts.

• Enoxaparin: 40 mg subcutaneously once daily. 20 mg once daily if creatinine clearance is under 30 mL/min. 40 mg every 12 hours (or 0.5 mg/kg every 12 hours) if body weight is over 100 kg.

• Dalteparin: 5000 units subcutaneously once daily.

• Unfractionated heparin: 5000 units subcutaneously every 8 to 12 hours, every 8 hours in higher risk.

• Fondaparinux: 2.5 mg subcutaneously once daily when heparin cannot be used.

• Anti-Xa monitoring: for obesity, kidney impairment, pregnancy, or low body weight, measure peak 4 hours after the third dose, aiming for 0.2 to 0.5 IU/mL.

Monitoring. Count platelets before starting and every 2 to 3 days for days 4 to 14, and check haemoglobin, creatinine and bleeding daily.

Stop rules. Stop heparin for active bleeding, or a platelet fall of more than 50 percent from baseline (usually days 5 to 10), which may be heparin-induced thrombocytopenia.

Referral and escalation. For suspected heparin-induced thrombocytopenia, stop all heparin including flushes and start argatroban 0.5 to 2 micrograms/kg/min (0.5 micrograms/kg/min in hepatic impairment) or fondaparinux under haematology direction. For confirmed pulmonary embolism, give treatment doses, for example enoxaparin 1 mg/kg every 12 hours.

Common errors. Not adjusting enoxaparin for kidney function or weight, omitting platelet counts, giving heparin around neuraxial procedures without timing, and continuing mechanical prophylaxis alone when drugs are safe.