Heparin dose response is independent of preoperative antithrombin activity in patients undergoing coronary artery bypass graft surgery using low heparin concentrations.

BACKGROUND: Unfractionated heparin's primary mechanism of action is to enhance the enzymatic activity of antithrombin (AT). We hypothesized that there would be a direct association between preoperative AT activity and both heparin dose response (HDR) and heparin sensitivity index (HSI) in patients undergoing coronary artery bypass graft surgery. METHODS: Demographic and perioperative data were collected from 304 patients undergoing primary coronary artery bypass graft surgery. AT activity was measured after induction of general anesthesia using a colorimetric method (Siemens Healthcare Diagnostics, Tarrytown, NY). Activated coagulation time (ACT), HDR, and HSI were measured using the Hepcon HMS Plus system (Medtronic, Minneapolis, MN). Heparin dose was calculated for a target ACT using measured HDR by the same system. Multivariate linear regression was performed to identify independent predictors of HDR. Subgroup analysis of patients with low AT activity (<80% normal; <0.813 U/mL) who may be at risk for heparin resistance was also performed. RESULTS: Mean baseline ACT was 135 ± 18 seconds. Mean calculated HDR was 98 ± 21 s/U/mL. Mean baseline AT activity was 0.93 ± 0.13 U/mL. Baseline AT activity was not significantly associated with baseline or postheparin ACT, HDR, or HSI. Addition of AT activity to multivariable linear regression models of both HDR and HSI did not significantly improve model performance. Subgroup analysis of 49 patients with baseline AT <80% of normal levels did not reveal a relationship between low AT activity and HDR or HSI. Preoperative AT activity, HDR, and HSI were not associated with cardiac troponin I levels on the first postoperative day, intensive care unit duration, or hospital length of stay. CONCLUSION: Although enhancing AT activity is the primary mechanism by which heparin facilitates cardiopulmonary bypass anticoagulation, low preoperative AT activity is not associated with impaired response to heparin or to clinical outcomes when using target ACTs of 300 to 350 seconds.

Frequency and timing of activated clotting time levels for sheath removal.

Guidelines currently exist that describe the medical management of patients undergoing percutaneous coronary interventions (PCI), but these guidelines do not include nursing management of the patient post procedure. The nursing staff on an intermediate care unit believed there were numerous and unnecessary activated clotting time (ACT) levels obtained on post PCI patients. The purpose of this study was to identify the most appropriate time to begin analyzing ACT levels. Results from a retrospective chart audit of 44 patients indicated that 3 hours after the last dose of heparin, only 7% of the patients met the criteria of ACT < 150 seconds in order to have their femoral sheaths removed, and 21% of patients had an ACT of < 160 seconds. It is recommended that current standard orders be changed to begin drawing ACT levels at 3 hours post last heparin dose and removing sheaths when ACT is < 160 seconds. This change would save the hospital nearly dollars 5000 in nursing time alone.