Does preoperative hemoglobin independently predict short-term outcomes after coronary artery bypass graft surgery?

BACKGROUND: The role of preoperative hemoglobin in predicting short-term coronary artery bypass graft (CABG) surgery outcomes has not been well established. This study investigated the association between preoperative hemoglobin level with 30-day operative mortality and perioperative complications.
METHODS: For the period from 1997 to 2005, the Department of Veterans Affairs Continuous Improvement in Cardiac Surgery Program database was used to extract 36,658 CABG-only deidentified records for patients undergoing cardiopulmonary bypass. Univariate and multivariate statistical models were used to predict both mortality and morbidity outcomes for varying levels of hemoglobin.
RESULTS: Unadjusted odds of 30-day operative mortality for patients with preoperative hemoglobin level less than 10 g/dL were 2.37 times higher than for patients with hemoglobin levels of 10 g/dL or greater (95% confidence interval: 1.84 to 3.05; p < 0.0001). Multivariable effect upon 30-day operative mortality decreased considerably (odds ratio = 1.29, 95% confidence interval: 0.99 to 1.68; p = 0.064).
CONCLUSIONS: As several risk factors may occur concurrently with low hemoglobin, preoperative hemoglobin level less than 10 g/dL was not a strong independent predictor of 30-day operative mortality or perioperative morbidity in multivariate models for on-pump CABG-only patients. Hemoglobin and serum creatinine were correlated, with creatinine exhibiting the stronger association with mortality. These findings suggest that moderate or severe anemia may be intertwined with other risk factors, such as serum creatinine or congestive heart failure. For a CABG patient subgroup presenting with a complex clinical preoperative profile, therefore, risk-model approaches may be inherently limited in separately identifying the predictors of anemic patients' outcomes.