Blood Conservation and Hemostasis in Cardiac Surgery: A Survey of Practice Variation and Adoption of Evidence-Based Guidelines.

BACKGROUND: Blood conservation and hemostasis are integral parts of reducing avoidable blood transfusions and the associated morbidity and mortality. Despite the publication of blood conservation guidelines for cardiac surgery, evidence suggests persistent variability in practice patterns. Members of the Society of Cardiovascular Anesthesiologists (SCA) created a survey to audit conformance to existing guidelines and use the results to help narrow the evidence-to-practice gap. METHODS: Members of the SCA and its Continuous Practice Improvement (CPI)- Blood Conservation Work Group developed a 48-item Blood Conservation and Hemostasis in Cardiac Surgery (BCHCS) survey. The questionnaire included the components of the Anesthesia Quality Institute's (AQI) composite measure AQI49. The survey was distributed to the entire SCA membership by e-mail via the Research Electronic Data Capture (REDCap) Consortium between the fall of 2017 and early 2018. RESULTS: Of 3152 SCA members, 536 returned surveys for a response rate of 17%. Most responders worked at academic institutions. The median transfusion trigger after cardiopulmonary bypass was hemoglobin (Hgb) 7.0 to 8.0 g/dL. There are 4 components to AQI49, and the composite conformance to all of them was low due to 1 specific component: the use of transfusion algorithms supplemented with point-of-care (POC) testing. There was good conformance to the other 3 components of AQI49: use of antifibrinolytics, minimization of hemodilution and use of red cell salvage. Overall, practices with a multidisciplinary patient blood management (PBM) team were the most successful in meeting all 4 AQI49 criteria. CONCLUSIONS: The survey demonstrated widespread adoption of several best practices, including the tolerance of lower hemoglobin transfusion triggers, use of antifibrinolytics, minimization of hemodilution, and use of red cell salvage. The survey also confirms that gaps remain in preoperative anemia management and the use of transfusion algorithms supplemented with POC hemostasis testing. Serial use of this survey can be used to identify barriers to implementation and audit the effectiveness of interventions described in this article. This instrument could also help harmonize local, regional, and national efforts and become an essential component of an implementation strategy for PBM in cardiac surgery.

Analysis of an engineered plasma kallikrein inhibitor and its effect on contact activation.

Engineering of protein-protein interactions is used to enhance the affinity or specificity of proteins, such as antibodies or protease inhibitors, for their targets. However, fully diversifying all residues in a protein-protein interface is often unfeasible. Therefore, we limited our phage library for the serine protease inhibitor ecotin by restricting it to only tetranomial diversity and then targeted all 20 amino acid residues involved in protein recognition. This resulted in a high-affinity and highly specific plasma kallikrein inhibitor, ecotin-Pkal. To validate this approach we dissected the energetic contributions of each wild type (wt) or mutated surface loop to the binding of either plasma kallikrein (PKal) or membrane-type serine protease 1. The analysis demonstrated that a mutation in one loop has opposing effects depending on the sequence of surrounding loops. This finding stresses the cooperative nature of loop-loop interactions and justifies targeting multiple loops with a limited diversity. In contrast to ecotin wt, the specific loop combination of ecotin-Pkal discriminates the subtle structural differences between the active enzymes, PKal and Factor XIIa, and their respective zymogen forms. We used ecotin-Pkal to specifically inhibit contact activation of human plasma at the level mediated by plasma kallikrein.

Active plasma kallikrein localizes to mast cells and regulates epithelial cell apoptosis, adipocyte differentiation, and stromal remodeling during mammary gland involution.

The plasminogen cascade of serine proteases directs both development and tumorigenesis in the mammary gland. Plasminogen can be activated to plasmin by urokinase-type plasminogen activator (uPA), tissue-type plasminogen activator (tPA), and plasma kallikrein (PKal). The dominant plasminogen activator for mammary involution is PKal, a serine protease that participates in the contact activation system of blood coagulation. We observed that the prekallikrein gene (Klkb1) is expressed highly in the mammary gland during stromal remodeling periods including puberty and postlactational involution. We used a variant of ecotin (ecotin-PKal), a macromolecular inhibitor of serine proteases engineered to be highly specific for active PKal, to demonstrate that inhibition of PKal with ecotin-PKal delays alveolar apoptosis, adipocyte replenishment, and stromal remodeling in the involuting mammary gland, producing a phenotype resembling that resulting from plasminogen deficiency. Using biotinylated ecotin-PKal, we localized active PKal to connective tissue-type mast cells in the mammary gland. Taken together, these results implicate PKal as an effector of the plasminogen cascade during mammary development.