Study population
In consecutive 866 adult patients (age ≥ 18 years) who underwent screening, we excluded 289 unsuitable patients. Therefore, the study included 577 patients and 96 of them developed to severe AKI (16.6%) within 7 days in ICU. The flowchart of this study and the number of patients is presented in Fig.1. Admission diagnoses of the patients included surgery (14.7%), sepsis (10.6%), cardiovascular disease (11.8%), trauma (22.7%), respiratory diseases (8.8%), neurological diseases (21%) and other causes (10.4%).
Patient characteristics
Patient characteristics are listed in Table 1. Severe AKI group enrolled 96 (16.6%) patients and no severe AKI group enrolled 481 (83.4%) patients. Compared with patients of no severe AKI group, patients of severe AKI group were significantly older, had a higher body mass index and had more CKD, sepsis and hypotension (MAP<70mmHg). ICU patients in the severe AKI group also had a higher SCr level, lactate level, NephroCheck value and PCT level on admission.
Table 1 Baseline characteristics and outcomes of the study population by presence or absence of severe AKI within 7 days
|
Variable
|
Severe AKI
|
No Severe AKI
|
P Value
|
N
|
96(16.6)
|
481(83.4)
|
|
Age (years)
|
73(58-81)
|
67(51-77)
|
0.004
|
Male
|
64(66.7)
|
301(62.6)
|
0.448
|
BMI (kg/m2)
|
26.18(23.03-29.41)
|
24.8(22.86-27.68)
|
0.037
|
SAPSII
|
44(34-52)
|
38(27-50)
|
0.153
|
Chronic risk factors
|
|
|
|
Age>65years
|
66(68.8)
|
256(53.2)
|
0.005
|
BMI>30kg/m2
|
21(21.9)
|
61(12.7)
|
0.039
|
Hypertension
|
48(50)
|
212(44.1)
|
0.49
|
DM
|
21(21.9)
|
66(13.7)
|
0.138
|
CKD
|
20(20.8)
|
39(8.1)
|
<0.001
|
Lung diseases
|
8(8.3)
|
43(8.9)
|
0.848
|
CVD
|
10(10.4)
|
58(12.1)
|
0.649
|
Acute risk factors
|
|
|
|
Sepsis
|
20(20.8)
|
41(8.5)
|
<0.001
|
Surgery
|
18(18.8)
|
67(13.9)
|
0.224
|
Vasopressor
|
46(47.9)
|
179(37.2)
|
0.05
|
Mechanical ventilation
|
71(74)
|
329(68.4)
|
0.281
|
MAP<70mmHg
|
40(41.7)
|
109(22.7)
|
<0.001
|
Biochemical indicators
|
|
|
|
Serum creatinine, admission(mg/dl)
|
1.08 (0.75-1.45)
|
0.83(0.65-1.08)
|
<0.001
|
Serum lactate, admission (mmol/l)
|
2.1(1.4-3.8)
|
1.6(1.2-2.6)
|
0.001
|
NephroCheck value, admission((ng/ml)2/1000)
|
0.66(0.23-2.49)
|
0.29(0.08-0.86)
|
<0.001
|
PCT, admission(ug/l)
|
1.19(0.28-6.81)
|
0.26(0.10-1.45)
|
<0.001
|
Nephrocheck (+)
|
69(71.9)
|
233(48.4)
|
<0.001
|
PCT (+)
|
54(56.3)
|
115(23.9)
|
<0.001
|
Outcomes
|
|
|
|
CRRT
|
11(11.5)
|
6(1.2)
|
<0.001
|
Death
|
32(33.3)
|
63(13.1)
|
<0.001
|
LOS(d)
|
5(2-8)
|
3(2-7)
|
0.034
|
Data are expressed as n (%) or median (interquartile range).
BMI, body mass index; SAPS II, simplified acute physiology score II; DM, diabetes mellitus; CKD, chronic kidney disease; CVD, cardiovascular disease; MAP, mean arterial pressure; PCT, procalcitonin; CRRT, continuous renal replacement therapy; LOS, length of stay.
Severe AKI within 7 days is associated with poor outcomes in ICU patients
Table 1 shows 11.5% of patients in severe AKI group and 1.2% of patients in no severe AKI group required CRRT (P <0.001). Severe AKI was also associated with ICU mortality. The mortality incidence was 33.3% in severe AKI group and 13.1% in no severe AKI group respectively (P <0.001). Severe AKI also increased LOS in ICU. LOS of severe AKI group and no severe AKI group were 5 (2-8) and 3 (2-7) respectively (P = 0.034).
Univariate variables associated with severe AKI within 7 days
Table 2 provides a list of significant univariate variables associated with severe AKI within 7 days. The presence of hypertension, CVD, lung disease, high-risk surgery, mechanical ventilation and SAPSII cannot predict the development of AKI in our study. Among the chronic risk factors, age >65 years, BMI>30 kg/m2, DM and CKD could predict severe AKI, the relative risk was 1.934 (95% CI(1.212-3.085,) P = 0.006), 1.887 (95% CI(1.085-3.282), P = 0.025), 1.748 (95% CI (1.009-3.027), P=0.046), 2.982 (95% CI (1.651-5.388), P < 0.001). Among the acute risk factors, sepsis and MAP<70mmHg could predict severe AKI, with a relative risk of 2.824 (95% CI (1.570-5.081), P=0.001) and 2.431 (95% CI (1.537-3.845), P<0.001). Among biochemical indicators, elevated SCr level was associated with a relative risk of 1.697 of developing severe AKI (95% CI (1.263-2.28), P<0.001). For increase in serum lactate concentration, there was a 11.5% increased relative risk of developing severe AKI (OR=1.115, 95% CI (1.036-1.199), P=0.003). In addition, NephroCheck (+) predicts the development of severe AKI with a relative risk of 2.72 (95% CI (1.684-4.394), P<0.001). PCT (+) predicts the development of severe AKI with a relative risk of 4.883 (95% CI (2.625-9.084), P<0.001).
Table 2 Logistic regression analysis for predictor of severe AKI within 7 days
Variable
|
Univariate
|
Multivariate
|
Chronic risk factors
|
|
|
Age>65years
|
1.934 (1.212-3.085)
|
1.961(1.153-3.336)
|
BMI>30kg/m2
|
1.887 (1.085-3.282)
|
NS
|
DM
|
1.748 (1.009-3.027)
|
NS
|
CKD
|
2.982 (1.651-5.388)
|
2.573(1.319-5.018)
|
Acute risk factors
|
|
|
Sepsis
|
2.824 (1.570-5.081)
|
NS
|
MAP<70mmHg
|
2.431 (1.537-3.845)
|
NS
|
Biochemical indicators
|
|
|
Serum creatinine, admission(mg/dl)
|
1.697 (1.263-2.281)
|
NS
|
Serum lactate, admission (mmol/l)
|
1.115 (1.036-1.199)
|
NS
|
Nephrocheck (+)
|
2.720 (1.684-4.394)
|
2.139(1.260-3.630)
|
PCT (+)
|
4.883 (2.625-9.084)
|
3.223(1.643-6.321)
|
Data are expressed as odds ratio (95% CI). NS: Nonsignificant predictors.
BMI, body mass index; DM, diabetes mellitus; CKD, chronic kidney disease; MAP, mean arterial pressure; PCT, procalcitonin.
Independent predictors of severe AKI within 7 days
Multivariate logistic regression was performed with univariate variables related to severe AKI within seven days. Following the variable selection, 4 independent predictors, including age >65 years (OR=1.961, 95% CI (1.153-3.336), P=0.013), CKD (OR=2.573, 95% CI (1.319-5.018), P=0.006), NephroCheck (+) on admission (OR=2.139, 95% CI (1.260-3.630), P =0.005) and PCT (+) on admission (OR=3.223, 95% CI (1.643-6.321), P=0.001), predicted the development of severe AKI (Table 2).
NephroCheck level on admission was associated with incidence of severe AKI within 7 days and its poor outcomes
For the 577 patients, 275 (47.7%) were NephroCheck≤0.3 (ng/ml)2/1000, 220 (38.1%) were NephroCheck (0.3-2) (ng/ml)2/1000 and 82 (14.2%) were NephroCheck≥2(ng/ml)2/1000. Severe AKI incidence within seven days, CRRT initiation and ICU mortality were highest in NephroCheck≥2(ng/ml)2/1000 group. The incidence of severe AKI within seven days increased from 9.8% in NephroCheck ≤0.3 (ng/ml)2/1000 patients to 19.1% in NephroCheck (0.3-2) (ng/ml)2/1000 patients and 32.9% in NephroCheck≥2(ng/ml)2/1000 patients (compared in 3 groups, P < 0.001). The treatment of CRRT increased from 1.1% in NephroCheck ≤0.3 (ng/ml)2/1000 patients to 2.7% in NephroCheck (0.3-2) (ng/ml)2/1000 patients and 9.6% in NephroCheck≥2(ng/ml)2/1000 patients (compared in 3 groups, P < 0.001). ICU mortality increased from 13.5% in NC (-) patients to 16.8% in NephroCheck (0.3-2) (ng/ml)2/1000 patients and 25.6% in NephroCheck≥2(ng/ml)2/1000 patients (compared with 3 groups, P = 0.033) (Fig. 2).
Incorporation of risk factors augments the predictive performance of the NephroCheck
Compared to NephroCheck (+) only (AUC=0.66, 95% CI:0.60-0.72), the combination of NephroCheck (+) and risk factors (age>65years, CKD and PCT positive) (AUC=0.75, 95% CI:0.70-0.81) led to a significant increase in the area under ROC curve for severe AKI prediction within 7 days (Fig. 3).