Heparin thromboprophylaxis in gastric bypass surgery

Patients undergoing gastric bypass surgery are at risk for postoperative venous thromboembolism. Thromboprophylaxis often includes fixed doses of some type of heparin. However, it is unlikely that the same dose of subcutaneous heparin will be optimal for all patients, because heparin pharmacokinetics depend on a number of patient variables, including thickness of the adipose layer.

An adjusted-dose, unfractionated heparin protocol was developed using pharmacokinetic data from 245 medical and surgical patients. Heparin doses were adjusted to achieve subtherapeutic peak anti-factor Xa heparin activity levels of 0.11-0.25 units/mL. This protocol was then applied to a prospective series of 700 patients undergoing laparoscopic Roux-en-Y gastric bypass who had no history of thromboembolism. Heparin prophylaxis was begun the evening of the day of surgery.

No patients were diagnosed with a deep venous thrombosis, but 3 (0.4%) were diagnosed with a non-fatal pulmonary embolism. Heparin therapy was halted because of bleeding in 2.3% of patients but only half of these required blood transfusions (1% of total). No patient required reoperation. Minor wound hematomas occurred in 0.6%. There were no deaths from any cause in this series.

Use of a monitored, adjusted-dose unfractionated heparin prophylactic protocol in a laparoscopic gastric bypass patient population resulted in doses greater than those used in traditional fixed-dose protocols. However, bleeding and thromboembolism rates were very low and no patients died.