 If patients consent to do the additional testing, this will be marked on the consent form. These patients will have anti-Xa levels drawn before the first enoxaparin dose, and then at 4h, 6h, 12h, and 18h after the second dose of enoxaparin. If the 12h anti-Xa level is obtained and is less than 0.05 unitsmL, then the 18 hour blood test can be eliminated. The purpose of this section is to provide us with information to evaluate the pharmacokinetic curve of enoxaparin in obese patients over 18 hours. 