Venous thromboembolism in the ICU
Marcus D. Lancé, MD, PhD
Head of Research & Vice-Chair
Department of Anesthesiology, ICU & Perioperative Medicine, Hamad Medical Corporation
Clinical Professor of Anesthesiology, Qatar University
Associate Professor of Anesthesiology, Weill-Cornell Medicine-Qatar
Venous thromboembolism describes the clinical presentation of atypical clot formation in the venous system of multifactorial origin, mainly depending on the so-called Virchow triad: stasis, vessel wall injury and hypercoagulability. The term ‘venous thromboembolism’ covers deep venous thrombosis (DVT) and pulmonary embolism (PE), of which the latter mostly derives from clots in the DVT. In the critically ill, the incidence of DVT ranges from 3.6 to 50 percent. Despite seemingly adequate prophylaxis, the risk developing a DVT is still 4-15 percent. As a result, the incidence of PE ranges from 7-27 percent, of which only one third is clinically suspected. While the DVT per se is not dangerous, an undiscovered PE carries a 30 percent mortality risk (1).
Currently known risk factors like the underlying disease and co-morbidities play a major role, e.g., history of previous DVT, malignancy, ongoing infectious disease, cardiovascular disease and pregnancy (2). In the intensive care (ICU) setting, patients are frequently bed-bound, sedated and sometimes even paralyzed, reducing peripheral muscle activity and by this the flow in the peripheral veins. Furthermore, the use and duration of indwelling devices like central venous catheters is associated with increased clotting risk.
Regarding the prediction of DVT, a variety of scoring systems, like the Well’s score, the Padua score, and the Caprini score exist. Some of them are validated for medical, some for surgical patients and some give advice for prevention strategies (3). This might be important when balancing the risk of DVT against a bleeding risk. While mild bleeding after peripheral surgery might be acceptable, hemorrhage after intra-cranial surgery, for instance, might be devastating.
Principally, there is a choice between mechanical and pharmacological prevention strategies or a combination of both. For example, mechanical prophylaxis recommendations point more to the use of intermittent pneumatic stockings (IPS), which are more effective with lesser side effects than simple compression stockings (4). Whenever pharmacological treatment carries a too high a risk (e.g., fresh bleeding, traumatic brain injury), only mechanical prevention should be started. However, it is still a matter for debate whether the combination of IPS with pharmacological prophylaxis might be superior.
Among the pharmacological approach, 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 has a shorter half-life, necessitating at least two daily injections, while the LMWH schemes apply a once daily injection (5). However, the shorter half-life and the ease of reversal might be an argument for the use of UFH in patients at bleeding risk. Finally, LMWH’s carry a higher risk of bioaccumulation (6, 7).
The route of drug application seems to be another point of concern. In the critically ill, peripheral organ perfusion might be disturbed due to the disease or the therapy (i.e., vasoconstriction or edema) which both might render resorption unpredictable.
In conclusion, DVT and pulmonary embolism puts additional risk on the critically ill. Currently, there is no consensus about the best prevention in this vulnerable population.
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