Deep vein thrombosis(DVT) is a common complication in hospitalized medical patients. Consensus guidelines recommend using medications such as heparin or low-molecular-weight heparins (LMWH) to prevent DVT in these patients. Generally, these medications are given in a fixed dose that is the same for everyone. The appropriate dose of medication in patients with severe obesity is uncertain. There is some evidence that the use of standard fixed-doses in severely obese patients may not provide adequate protection against DVT. The purpose of this study is to evaluate a weight-based dose(0.5 milligrams per kilogram of body weight) of the commonly prescribed LMWH, enoxaparin in severely obese patients to determine if predictable levels of blood thinning can be achieved. We hypothesize that dosing enoxaparin 0.5mg/kg once daily in severely obese patients will lead to predictable blood levels.