Preoperative Anemia in Cardiac Operation: Does Hemoglobin Tell the Whole Story?

BACKGROUND

Preoperative anemia, defined by hemoglobin level, is associated with elevated risk after cardiac operation. Better understanding of anemia requires characterization beyond this. This investigation focuses on red cell size and its association with patient characteristics and outcomes after cardiac operation.

METHODS

From January 2010 to January 2014, 10,589 patients underwent elective cardiac operations at Cleveland Clinic. Anemia was characterized as normocytic, microcytic, or macrocytic based on mean corpuscular volume (MCV). Models for hospital complications were developed using multivariable logistic regression. Other outcomes were postoperative transfusion and intensive care unit (ICU) and postoperative hospital lengths of stay.

RESULTS

A total of 2,715 patients (26%) were anemic. Of these, 2,365 (87%) had normocytic, 219 (8.1%) microcytic, and 131 (4.8%) macrocytic anemia. Non-anemic patients (n = 2,041, 26%) received transfusions compared with 1,553 (66%) normocytic, 148 (68%) microcytic, and 97 (74%) macrocytic anemia patients. Patients with normocytic or macrocytic anemia had more renal failure (normocytic: odds ratio (OR) 1.9, macrocytic: OR 3.5), other complications (normocytic: OR 1.3, macrocytic: OR 2.2) and death (normocytic: OR 2.0, macrocytic: OR 6.2) than non-anemic patients; patients with microcytic anemia had fewer reoperations (OR 0.35) and less postoperative atrial fibrillation (OR 0.50). Anemic patients experienced longer ICU (27 versus 48 hours, p < 0.001) and postoperative hospital (6.1 versus 7.4 days, p < 0.001) length of stay than non-anemic patients.

CONCLUSIONS

Cardiac surgical patients are often anemic. Demographic characteristics, comorbidities, and outcomes are dissimilar according to red cell size. Patients with microcytic anemia had the lowest hemoglobin levels, yet the best clinical outcomes among anemic patients. MCV from the standard complete blood count adds additional information beyond hemoglobin for targeted intervention.