Table 2.

List of candidate variables based on univariate logistic regression analysis compared with random forest.

Variable		Type	Unit	Univariate logistic regression analysisa			Random forest
				OR (95% CI)	P value	Rank	Decrease of impurity, %	Nodes using that attribute, n	Rank
Age (years)		Continuous	Years	1.1 (1.03-1.07)	<.001	1b	43	3238	1
Mechanical ventilation >24 hours		Categorical	Yes/no	5.8 (3.9-8.6)	<.001	3	21	297	21
Preoperative creatinine clearance		Continuous	μmol/L	0.97 (0.96-0.98)	<.001	1b	39	2544	4
Length of stay in the ICUc		Ordinal	—d	—	—	2	26	590	20
	>72 hours	—	—	7.6 (4.9-11.9)	<.001	—	—	—	—
	24-72 hours	—	—	1.7 (0.9-2.8)	<.001	—	—	—	—
Procedure other than isolated CABGe		Categorical	Yes/no	2.9 (1.8-2.5)	<.001	6	28	370	15
Blood product within 48 hours		Categorical	Yes/no	2.9 (2.0-4.2)	<.001	5	28	452	14
Intraoperative TEEf		Categorical	Yes/No	2.0 (1.3-3.1)	.002	10	27	568	18
EURO IIg score		Continuous	Percent	1.07 (1.05-1.09)	<.001	17	41	2716	2
Preoperative hemoglobin		Continuous	gm/dL	0.98 (0.97-0.99)	<.001	1b	40	2766	3
Preoperative A-Fibh		Categorical	Yes/no	2.3 (1.4-3.6)	<.001	7	35	486	6
Timing of IABPi		Ordinal	—	—	—	4	29	329	12
	Preoperative	—	—	1.4 (0.6-2.9)	.42	—	—	—	—
	Intraoperative	—	—	6.8 (1.9-23.1)	.002	—	—	—	—
Intraoperative inotropes		Categorical	Yes/no	2.1 (1.4-3.0)	<.001	8	27	514	17
COPDj		Categorical	Yes/no	1.7 (1.1-2.7)	.02	14	33	689	9
CVDk		Categorical	Yes/no	1.8 (1.1-2.9)	.01	13	29	516	13
DMl		Categorical	Yes/no	0.9 (0.6-1.4)	.79	16	39	995	5
Frail		Categorical	Yes/no	2.0 (1.1-3.5)	.03	12	30	381	11
History of turn down		Categorical	Yes/no	8.2 (2.8-24.3)	<.001	1b	21	93	22
EFm categories		Ordinal	—	—	—	9	33	89	10
	30%-50%	—	—	1.4 (0.9-2.1)	.18	—	—	—	—
	<30%	—	—	2.1 (1-4.2)	.04	—	—	—	—
Gender		Categorical	Yes/no	1.2 (0.8-1.9)	.47	16	35	752	7
Aortic stenosis		Ordinal	—	—	—	14	26	899	16
	Moderate	—	—	1.4 (0.6-2.8)	.43	—	—	—	—
	Severe	—	—	1.6 (1.1-2.5)	.01	—	—	—
Mitral insufficiency		Ordinal	—	—	—	15	26	899	19
	Moderate	—	—	1.4 (0.9-2.1)	.07	—	—	—	—
	Severe	—	—	2.3 (1.02-4.6)	.03	—	—	—	—
Postoperative arrhythmias		Categorical	Yes/no	1.8 (1.3-2.8)	.002	11	34	746	8

^aAnalysis was done using univariate logistic regression with a P value of <.05 considered to be statistically significant.

^bThese variables were all equally ranked as 1st because they had almost equal odds ratios and a P value of <.001.

^cICU: intensive care unit.

^dNot applicable.

^eCABG: coronary artery bypass graft.

^fTEE: transesophageal echo.

^gEURO II: European System for Cardiac Operative Risk Evaluation II.

^hA-Fib: atrial fibrillation.

ⁱIABP: intra-aortic balloon pump.

^jCOPD: chronic obstructive pulmonary disease.

^kCVD: cerebrovascular disease.

^lDM: diabetes mellitus.

^mEF: ejection fraction.