2.5. Statistical analysis

Baseline characteristics were compared using 2-tailed χ² tests for categorical variables and t tests for continuous variables. The Wilcoxon rank sum test was used to compare the median Hgb during each of the 4 periods: the first 2 hours, the first 6 hours, between 6 and 12 hours, and between 12 and 24 hours postarrest. Hemoglobin concentration was investigated as a continuous predictor of neurologic outcome and then as a dichotomized predictor, first with a cutoff of 7 g/dL and again with a cutoff of 10 g/dL. These cutoffs were determined a priori and loosely based on prior transfusion trials in critically ill populations [12,13,15].

Multivariate logistic regression was used to test for the association between Hgb neurologic outcome and hospital mortality at each of the 4 time points. The analyses were adjusted for the following covariates: age, initial cardiac rhythm, cardiac etiology of arrest, location of arrest (inhospital or out of hospital), receipt of TTM, hematologic or metastatic malignancy, or preexisting renal insufficiency. All analyses were conducted using STATA 12.0 (College Station, TX).