Mechanisms behind operating room blood transfusions in coronary artery bypass graft surgery patients with insignificant bleeding

Objective: To investigate situations in cardiac surgery when transfusions are sometimes used for indications other than to compensate for surgical bleeding.

Design: Retrospective study.

Setting: Cardiac surgery unit at a university teaching hospital.

Participants: Patients scheduled for coronary artery bypass graft surgery (n = 2,469).

Interventions: A subgroup of patients with surgical bleeding of < or = 400 mL (n = 982) was selected to identify mechanisms leading to perioperative erythrocyte transfusion.

Measurements and main results: Bleeding of >400 mL triggered transfusion. At less than this bleeding volume, other indications were noted: unstable angina, use of blood cardioplegia, and bad surgical outcome, such as inotropic support. After exclusion of these predictors and anemic patients, the strongest predictors were female gender (p < 0.001), weight < or = 70 kg (p < 0.001), cardiopulmonary bypass (CPB) time > or = 90 minutes (p = 0.002), CPB cooling < or = 32 degrees C (p = 0.038), and advanced age (p < 0.001). Results from a more detailed study of medical records showed that within its normal concentration range, the operating room-transfused patients had lower hemoglobin levels. When followed postoperatively in the intensive care unit and ward, these patients continued to receive more transfusions (p < 0.05) even though their bleeding in the intensive care unit did not differ from the control subjects.

Conclusion: Some patients are transfused because of institutional bias of an anticipated need rather than for true surgical bleeding. A concern of hemodilution from standard CPB circuits suggests a possible advantage with low-priming volume for smaller adult female patients.