Critically ill patients who are admitted to an intensive care unit (ICU) are at high risk for deep vein thrombosis (DVT), with an estimated 20-40% of patients developing DVT without prophylaxis. Preventing DVT is important because DVT is usually clinically silent in such patients, and its first manifestation may be life-threatening pulmonary embolism.

About 30% of ICU patients have renal insufficiency, based on a calculated creatinine clearance (CrCl), and such patients have 4-fold higher risk of DVT than those with normal renal function.

The current anticoagulant regimen that is used to prevent DVT in such patients, consisting of unfractionated heparin (UFH), 5000 IU twice-daily, may be inadequate.

A recent prospective cohort study by our research group that investigated the risk of DVT in 261 ICU patients found that 10% of patients developed proximal vein DVT after admission to the ICU despite receiving UFH, 5000 IU twice-daily.

In other patient groups at high risk for DVT, low-molecular-weight heparins (LMWHs) have replaced UFH for DVT prophylaxis because of superior efficacy.

Despite superior efficacy and safety in many patients, there is concern about using LMWHs in patients with renal insufficiency because LMWHs are cleared by the kidney. LMWH use in such patients might result in an excessive anticoagulant effect, with the potential to increase bleeding.

Much of the concern about the safety of LMWH in patients with renal insufficiency pertains to therapeutic-dose LMWH used to treat DVT. Prophylactic-(or low) dose LMWH that is used to prevent DVT in ICU patients is about 25-33% of a therapeutic-dose.

Three sources of evidence suggest that prophylactic-dose LMWH may be safe in patients with renal insufficiency. First, current evidence does not support the fact that prophylactic-dose LMWH accumulates and should be avoided in such patients. Second, prophylactic-dose LMWH appears to be safe in hemodialysis patients. Third, preliminary work by our research group suggests that dalteparin, 5000 IU once-daily, does not accumulate in ICU patients with renal insufficiency. Thus, 0 of 10 ICU patients with a CrCl <50 mL/min/1.73m2 who received dalteparin had a detectable trough anticoagulant effect (anti-Xa >0.10 IU/mL). Further, when the relationship between CrCl and peak anti-Xa levels was assessed, there was no correlation (r<0.2). Finally, in 2 patients with severe renal insufficiency (CrCl<30 mL/min/1.73m2) who received dalteparin, 5000 IU once-daily, all 9 trough anti-Xa values were <0.10 IU/mL.

No study has investigated the safety of low-dose LMWH in ICU patients with impaired renal function; until such a study is completed, randomized trials assessing the efficacy of low-dose LMWH for DVT prophylaxis among ICU patients will not be feasible.

As a first step in addressing this problem, we propose an open-label pilot study to assess the safety of dalteparin prophylaxis, 5000 IU once-daily, in ICU patients with severe renal insufficiency.

The safety of the proposed dalteparin prophylaxis regimen will be assessed by determining the risk of an excessive anticoagulant effect and the risk of major bleeding. Dalteparin prophylaxis will be considered safe if 2 criteria are satisfied by the end of the treatment period:

• proportion of patients with trough anti-Xa level >0.40 IU/mL is ~10% or less (exclude 17% with 95% confidence);
• risk of major bleeding is ~4% or less (exclude 10% with 95% confidence).

If we show that dalteparin prophylaxis is safe in ICU patients with severe renal insufficiency, this will improve patient care in 2 ways:

• dalteparin may reduce the risk of DVT (although this should be tested in future trials); and
• dalteparin would reduce heparin induced thrombocytopenia (HIT), an infrequent but serious complication of UFH.