oa DVT prophylaxis in critical care: role of NOACS

The incidence of deep vein thrombosis (DVT) in the critically ill ranges from 3.6% to 37%. Despite seemingly adequate prophylaxis the risk for DVT is still between 4 and 15%.

Currently the known risk factors can be divided into inherited and acquired. In addition, the underlying disease and comorbidities play a major role, e.g., history of DVT, malignancy, ongoing infectious disease, cardiovascular disease and pregnancy¹.

DVT prevention is applied in various ways and timings. Principally, the choice is between mechanical, pharmacological and a combination of both.

Regarding the mechanical prophylaxis, recommendations point more to the use of intermittent pneumatic stockings (IPS), which are more effective with less side effects than simple stockings². Whenever pharmacological treatment carries a relatively high risk (e.g., fresh bleeding, traumatic brain injury) mechanical prevention might be started. However, it is still under debate whether the combination of IPS with pharmacological prophylaxis is superior.

Like all anticoagulant therapy, the risk (and consequences) of DVT should be balanced against the risk of bleeding. A variety of scoring systems, like the Well's score, the Caprini score and the Has-Bled score exist to group the risks. In terms of risk assessment, bleeding after peripheral surgery might be less dangerous than after intracranial surgery.

In general, low molecular weight heparins (LMWH) are preferred above unfractionated heparin (UFH). One reason might be the risk of heparin induced thrombocytopenia (HIT), which is higher with UFH than with LMWH. On the other hand, UFH have a shorter half-life necessitating at least two daily injections, while the LMWH schemes apply a once daily injection³. However, the shorter half-life and the ease of reversal might be an argument for UFH use in patients at bleeding risk. In contrast, LMWH's carry a higher risk of bioaccumulation^4,5. The route of application seems to be another point of concern. In the critically ill, peripheral organ perfusion might be disturbed by the disease or the therapy (i.e. vasoconstriction or edema).

It is still a debate if oral anticoagulants should be used in critical care. Mainly concerns are raised from pharmacological considerations. For instance, if enteral feeding is only possible via tubes, grinding of tablets will change the galenic of the drugs and their bioavailability. In addition, it is not clear whether orally applied drugs will be resorbed completely. Excretion of drugs might be altered due to impairment of kidney and/or liver function which could result in their accumulation.

Finally, changes in the coagulation system due to the underlying disease might occur unexpectedly and therefore unanticipated.

In concert with difficulties in laboratory measurement and reversal of the drug benefits of oral anticoagulants do not outweigh risks and disadvantages. Therefore, it seems not recommendable to start any kind of oral anticoagulation before the patient's condition is stable enough which is mostly the moment of discharge from the ICU.