What Drives Variability in Postoperative Cardiac Surgery Transfusion Rates?

Objective Wide inter-hospital variation exists in cardiac surgical postoperative transfusion rates. We aimed to compare transfusion rates at two hospitals and identify the institutional practice factors, unrelated to patient or operative characteristics, associated with postoperative transfusion rates. Methods Records for adult patients undergoing routine cardiac surgery at two hospitals (H and L) from 2/2020 to 8/2022 were analyzed. Patient and operative characteristics, pre-operative and ICU hemoglobin values, and postoperative transfusion rates were compared. Transfusion indication was recorded prospectively. Propensity matching was completed to assess comparability of patient populations. Results After propensity matching patients at H and L on age, procedure type, predicted morbidity or mortality, cross-clamp time, pre-operative hypertension, pre-operative heart failure, and pre-operative stroke, 2,111 patients remained, with similar characteristics except hypertension. Matched results showed no significant differences in mortality, reoperation, or other major outcomes. Hospital H transfused 36% of patients (mean postoperative Hb 10.5), with 1,483 units of PRBCs while Hospital L transfused 12% of patients (mean postoperative Hb 9.4), with 198 units of PRBCs (p<0.001). For all patients with a Hb>7.5, Hospital H versus L transfused 27% versus 0.9% (p<0.001). Hospital L’s sole transfusion indication for pTxHb>7.5 was bleeding vs Hospital H, which had multiple indications. When Hb concentration alone was the indication for transfusion, the threshold at H was <7.5 g/dL versus <6 g/dL at L. Conclusions Variation in transfusion rates between hospitals H and L resulted from strict adherence at Hospital L to a transfusion trigger of <6 g/dL with narrow indications for transfusions above that Hb concentration. Word Count= 249