Hemoglobin drift after cardiac surgery

Recent literature suggests that a restrictive approach to red blood cell transfusions is associated with improved outcomes in cardiac surgery patients. Even in the absence of bleeding, intravascular fluid shifts cause hemoglobin levels to drift postoperatively, possibly confounding the decision to transfuse. The purpose of this study was to define the natural progression of hemoglobin levels in postoperative cardiac surgery patients.

All cardiac surgery patients from October 2010 through March 2011 who did not receive a postoperative transfusion were included. Primary stratification was by intraoperative transfusion status. Change in hemoglobin was evaluated relative to the initial postoperative hemoglobin. Maximal drift was defined as the maximum minus the minimum hemoglobin for a given hospitalization. Final drift was defined as the difference between initial and discharge hemoglobin.

The final cohort included 199 patients: 71 (36%) received an intraoperative transfusion, whereas 128 (64%) did not. The average initial and final hemoglobin levels for all patients were 11.0±1.4 g/dL and 9.9±1.3 g/dL, respectively, giving a final drift of 1.1±1.4 g/dL. The maximal drift was 1.8±1.1 g/dL and was similar regardless of intraoperative transfusion status (p=0.9). Although all patients' hemoglobin initially dropped, 79% of patients reached a nadir and experienced a mean recovery of 0.7±0.7 g/dL by discharge. On multivariable analysis, increasing cardiopulmonary bypass time was significantly associated with total hemoglobin drift (coefficient/hour, 0.3 [0.1-0.5] g/dL; p=0.02).

In this report of hemoglobin drift after cardiac surgery, although all postoperative patients experienced downward hemoglobin drift, 79% of patients exhibited hemoglobin recovery before discharge. Physicians should consider the eventual upward hemoglobin drift before administering red blood cell transfusions.