PROphylaxis of ThromboEmbolism in Critical Care Trial (PROTECT)

Patients will undergo concealed random allocation to LMWH (dalteparin 5,000 IU once daily, the experimental intervention) subcutaneously. The control intervention represents standard thromboprophylaxis in Canada and Australia for these ICU patients, as we have documented in surveys [Cook 2001, Cooper 2005], cross-sectional studies [Cook 2001, Lacherade] and a longitudinal study [Cook 2003]. We will prepare LMWH syringes that contain 5,000 IU of dalteparin. UFH syringes will contain 5,000 IU of UFH. Syringes of LMWH and UFH will appear identical. Patients allocated to LMWH will also receive one placebo injection daily to maintain blinding. For patients allocated to LMWH, the first dose, or the morning dose in each study kit will always be placebo and nurses will administer the numbered doses sequentially. This is to optimize the likelihood that the patients enrolled later in the day into the LMWH arm will receive active drug on study day 1. Nurses will administer study drug at approximately 1100h (+1 hour) (placebo or UFH) and 2300h (+1 hour) (dalteparin or UFH). Study drug will be administered for the duration of the ICU stay. Bilateral proximal leg compression ultrasounds will be performed within 48hours of enrolment, twice weekly, and on suspicion of DVT.