College Answer

Many different strategies are employed and should be considered.  Reviews and recommendations are widely published (eg. Geerts, WH, Heit, JA, Clagett, GP, et al.   Prevention of venous thromboembolism. Chest 2001; 119:132S). Good placebo controlled RCTs are rare.

Simple techniques such as passive mobilisation, and early active mobilisation are encouraged but not well studied.  The use of elastic compression stockings (knee-length or whole leg) is simple, widespread and effective for low risk patients.  The addition of intermittent pneumatic compression devices has been recommended (limited evidence) where higher risk exists but other pharmacology is deemed contraindicated.  Most studies have assessed the use of low dose unfractionated heparin or low molecular weight heparins (though few studies have used placebo control).  LMW heparins (when compared with unfractionated heparin) seem to provide similar or better prophylaxis, with less thrombocytopaenia, though with a small increase in the incidence of bleeding.  Other agents including pentasaccharides or hirudin are showing promise.  Older agents such as dextran and warfarin are used less frequently.

Other controversies include cost-benefit, and side-effect profiles etc.

Discussion

A systematic approach to this answer would resemble the following:

Rationale:

• DVT develops in a large proportion of ICU patients in the absence of DVT prophylaxis:
  • 30% of general medical/surgical ICU patients
  • 50-65% of trauma patients
  • 20%-50% of neurosurgical patients
  • 80% of spinal cord injury patients
• VTE is a significant cause of ICU mortality and morbidity
• Even small emboli may be disastrous

Therapeutic options

• Unfractionated heparin
• Low molecular weight heparin
• Compression stockings
• Sequential pneumatic compression devices
• Early mobilisation

Advantages:

• Cost-effective prevention of mortality and morbidity

Disadvantages:

• Risk of bleeding with chemical methods
• Risk of DVT dislodgement with pneumatic compression
• Risk of falls with ealry mobilisation
• Risk of limb ischaemia with compression stockings
• Contraindicated in lower limb surgery or trauma

Evidence:

• The recommendation for early mobilisation is based on the knoweldge that immobility is associated with DVT, rather than on any sort of prospective trial evidence.
• Heparin of any sort is protective against DVT (16 studies with a combined n=34,369)
• No difference between LMWH and UHF (PROTECT trial)
• Intermittent compression stockings are better than nothing according to a recent prospective cohort study.
• Compression stockings in the ICU are purely decorative according to the same study, but in the general hospital population they are better than nothing, and have a cumulative benefit when used together with other methods of DVT prophylaxis.
• Authors trend towards the suggestion that a combination of chemical and mechanical methods is the best practice

The PROTECT trial (2011) is the most recent large entry into the DVT prophylaxis arena. It was negative- there was no difference between LMWH and UFH. However, a significant reduction in the incidence of PE was found with LMWH, which has led some authors to recommend it as the first choice in renally normal patients.