Evaluation of Anti-Xa Levels in Surgery Patients Receiving Fixed Dose Heparin

The purpose of this study is to determine if fixed dose heparin infusions at a rate of 500 units/hour are sufficient to maintain a target anti-Xa of 0.1-0.35 IU/mL for venous thromboembolism (VTE) prophylaxis in patients undergoing microvascular surgery. Additionally, a pilot protocol has been developed to titrate these heparin infusions to ensure patients have sufficient VTE prophylaxis. All patients will be enrolled in the observational arm of the study and receive anti-Xa level monitoring. Patients with out-of-range anti-Xa levels will cross over to the interventional arm of the study and receive real time heparin infusion dose adjustments per the pilot protocol. The primary outcome measured will be the percentage of patients with anti-Xa levels in the target range of 0.1-0.35 IU/mL while on a heparin infusion at 500 units/hour.

The investigators will identify surgical patients placed on fixed dose heparin infusions at their attending surgeon's discretion-the proposed research will not dictate the initiation of the heparin drip intraoperatively. However, the investigators will identify patients already on heparin, evaluate steady state heparin anti-Xa levels and adjust patient's dose if necessary based on steady state anti-Xa levels. Eligible patients will be started on heparin fixed-dose intraoperatively. Steady state anti-Xa levels will be drawn at least 6 hours after initiation of heparin infusion. Goal anti-Xa levels will be 0.1-0.35 IU/mL.

Patients with identified out of range levels will receive pharmacist-driven real time heparin dose adjustment and will receive follow-up steady state anti-Xa levels. Anti-Xa level monitoring will be discontinued when in range peak levels are obtained, when heparin infusions are discontinued at surgeon discretion, or when the patient is discharged.

Patients will have steady state anti-Xa levels drawn at least 6 hours after initiation of heparin infusion. Patients with out of range anti-Xa levels will receive real time heparin dose adjustment followed by repeat anti-Xa levels.

Inclusion Criteria: Patients undergoing surgical procedures Initiation of a heparin infusion at a rate of 500 units/hour intraoperatively or postoperatively Exclusion Criteria: Age <18 years old Pregnant Incarcerated Mentally disabled