Table 2.

Four Models Describing the Association of AKI Severity with Postoperative Outcome

	Mortality				Morbidity
	In-hospital Death		Survival*		Hospital Length of Stay†		Discharge‡
	P Value	OR (95% CI)	P Value	HR (95% CI)§	P Value	β (95% CI)	P Value	HR (95% CI)||
Constant#	<0.001	—	—	—	<0.001	9.75 (9.21–10.30)	—	—
Age, yr	0.002	0.99 (0.99 to 1.00)	0.39	1.00 (0.99 to 1.01)	0.30	−0.00 (−0.01 to 0.00)	<0.001	1.00 (1.00 to 1.00)
Sex, female vs. male	0.19	0.90 (0.77 to 1.05)	0.67	0.97 (0.84 to 1.12)	0.08	0.09 (−0.01 to 0.20)	0.27	0.99 (0.97 to 1.01)
Charlson Comorbidity Index	<0.001	1.18 (1.16 to 1.21)	<0.001	1.13 (1.11 to 1.15)	<0.001	0.17 (0.16 to 0.19)	<0.001	0.96 (0.96 to 0.96)
Congestive heart failure	<0.001	2.15 (1.77 to 2.61)	<0.001	1.61 (1.36 to 1.89)	<0.001	1.12 (0.91 to 1.33)	<0.001	0.85 (0.81 to 0.89)
Preoperative hemoglobin, mg/dl	<0.001	0.79 (0.76 to 0.86)	<0.001	0.87 (0.84 to 0.90)	<0.001	−0.38 (−0.40 to −0.35)	<0.001	1.09 (1.08 to 1.10)
Preoperative creatinine, mg/dl**	0.08	0.90 (0.80 to 1.01)	0.55	0.97 (0.88 to 1.07)	<0.001	−1.11 (−1.24 to −0.98)	<0.001	1.20 (1.17 to 1.24)
Radiocontrast agent††	<0.001	1.90 (1.61 to 2.25)	<0.001	1.48 (1.28 to 1.72)	<0.001	0.72 (0.55 to 0.89)	<0.001	0.87 (0.84 to 0.90)
Noncardiac vs. cardiac surgery	<0.001	1.94 (1.48 to 2.55)	0.002	1.43 (1.14 to 1.78)	<0.001	2.27 (1.99 to 2.54)	0.003	0.92 (0.87 to 0.97)
Risk factors of surgical AKI‡‡
1 risk factor	0.93	1.01 (0.83 to 1.23)	0.69	1.04 (0.97 to 1.49)	0.86	−0.01 (−0.13 to 0.11)	0.14	1.02 (0.99 to 1.05)
2 risk factors	0.09	1.23 (0.97 to 1.58)	0.10	1.20 (0.97 to 1.49)	<0.001	1.04 (0.79 to 1.28)	0.15	0.96 (0.92 to 1.01)
≥ 3 risk factors	<0.001	3.27 (2.28 to 4.69)	<0.001	1.98 (1.49 to 2.63)	<0.001	4.25 (3.55 to 4.96)	<0.001	0.65 (0.56 to 0.74)
Postoperative ICU admission	<0.001	2.54 (2.09 to 3.09)	0.004	1.31 (1.09 to 1.58)	<0.001	4.83 (4.69 to 4.98)	<0.001	0.57 (0.56 to 0.59)
Severity of AKI§§
No F/U	0.001	0.60 (0.45 to 0.81)	0.35	0.87 (0.65 to 1.16)	<0.001	−2.27 (−2.42 to −2.13)	<0.001	1.70 (1.65 to 1.75)
ΔCr 1–24%	0.49	0.92 (0.71 to 1.17)	0.19	0.85 (0.67 to 1.08)	0.001	0.28 (0.11 to 0.45)	0.81	1.00 (0.97 to 1.04)
ΔCr 25–49%	<0.001	1.74 (1.28 to 2.38)	0.04	1.36 (1.02 to 1.82)	<0.001	2.44 (2.12 to 2.75)	<0.001	0.80 (0.75 to 0.86)
KDIGO stage 1	<0.001	2.21 (1.69 to 2.87)	<0.001	1.55 (1.22 to 1.98)	<0.001	2.88 (2.58 to 3.17)	<0.001	0.77 (0.72 to 0.82)
KDIGO stage 2	<0.001	3.82 (2.65 to 5.52)	<0.001	2.24 (1.62 to 3.09)	<0.001	5.12 (4.52 to 5.71)	<0.001	0.65 (0.58 to 0.73)
KDIGO stage 3	<0.001	15.64 (12.07 to 20.28)	<0.001	4.46 (3.57 to 5.56)	<0.001	10.87 (10.36 to 11.37)	<0.001	0.38 (0.34 to 0.42)

On the left, a binary logistic regression model estimating the OR and a corresponding Cox proportional hazard regression model estimating the HR for all-cause in-hospital death; on the right, a robust regression model estimating the coefficients for hospital length of stay and a corresponding Cox proportional hazard model calculating the HR for hospital discharge.

^*A total of 37,772 cases were censored due to hospital discharge;

^†R² = 0.35;

^‡842 cases were censored due to in-hospital death;

^§HR for in-hospital death;

^||HR for discharge from hospital;

^#not applicable for Cox proportional hazard regression models;

^**International Systems of Units conversion factor: to convert creatinine to μM, multiply values by 76.3;

^††administered within 1 week before surgery;

^‡‡as described by Kheterpal et al.³;

^§§mutually exclusive categories of AKI severity by defnition of the KDIGO group.²⁷

AKI = acute kidney injury; Cr = creatinine; HR = hazard ratio; ICU = intensive care unit; KDIGO = Kidney Disease: Improving Global Outcome; no F/U = no follow-up; OR = odds ratio; SE = standard error.