Performance of the renal resistive index and usual clinical indicators in predicting persistent AKI

Figures & data

Figure 1. Flow chart. AKI: acute kidney injury.

Table 1. Patient characteristics.

	All patients (n = 102)	no P-AKI (n = 63)	P-AKI (n = 39)	p Value
Demographic data
Sex, male	69 (67.6)	42 (66.7)	27 (69.2)	0.788
Age, yr	70 ± 15	70 ± 14	71 ± 17	0.826
Hypertension	57 (55.9)	33 (52.4)	24 (61.5)	0.365
Mode for ICU admission				0.054
Emergency room	25 (24.5)	17 (27.0)	8 (20.5)
Operating room	46 (45.1)	32 (50.8)	14 (35.9)
Ward	29 (28.4)	14 (22.2)	15 (38.5)
Transferred from another center	2 (2.0)	0 (0.0)	2 (5.1)
Primary source of sepsis				0.095
Pulmonary	40 (39.4)	22 (34.9)	18 (46.2)
Intra-abdominal	36 (35.3)	28 (44.4)	8 (20.5)
Urinary	11 (10.8)	5 (7.9)	6 (15.4)
Other	15 (12.7)	8 (12.7)	7 (17.9)
Time from vasopressor initiation to inclusion, h	3.0 [2.0–5.0]	3.0 [2.0–5.0]	3.0 [1.0–5.0]	0.500
Clinical characteristics at inclusion
Heart rate, beats/min	110 ± 22	108 ± 23	115 ± 19	0.170
MAP, mmHg	79 ± 15	80 ± 14	77 ± 15	0.269
Hemoglobin, g/L	112 ± 28	113 ± 30	109 ± 26	0.508
Platelet, ×10^9 /L	174 ± 103	190 ± 103	147 ± 99	0.039
Total bilirubin, μmol/L	15.5 [9.7–24.1]	12.8 [9.2–20.2]	19.5 [12.2–41.1]	0.004
PaO2/FiO2, mmHg	225 ± 100	233 ± 97	212 ± 104	0.301
PaCO2,mmHg	40 ± 14	40 ± 13	39 ± 16	0.599
Lactate, mmol/L	2.3 [1.7–3.6]	1.9 [1.4–3.0]	2.3 [3.4–6.1]	<0.001
Procalcitonin, ng/mL	6.8 [1.5–16.9]	5.4 [1.0–12.1]	9.6 [1.8–34.0]	0.030
CVP, mmHg	9.9 ± 4.6	9.2 ± 4.7	11.0 ± 4.3	0.047
APACHEII score	16.3 ± 4.8	16.1 ± 4.6	16.7 ± 5.2	0.586
SOFA score	8.5 ± 3.5	6.9 ± 2.4	11.0 ± 3.6	<0.001
nonrenal SOFA score	7.8 ± 3.3	6.6 ± 2.4	9.7 ± 3.5	<0.001
Kidney function
Baseline sCr, μmol/L	72.7 ± 16.1	70.6 ± 17.4	76.1 ± 13.3	0.096
Based back-calculation	23 (22.5)	12 (19.0)	11 (28.2)	0.282
Serum creatinine, µmol/L	119.5 ± 72.5	91.5 ± 34.3	160.6 ± 92.5	<0.001
Organ support and treatment at inclusion
Norepinephrine dose, µg/kg/min	0.25 [0.10–0.50]	0.20 [0.10–0.35]	0.48 [0.14–0.90]	0.006
Mechanical ventilation	92 (90.2)	57 (90.5)	35 (89.7)	1.000
Time from inclusion to hemodynamic stabilization, h	1.0 [0.0–3.0]	1.0 [0.0–2.0]	3.0 [1.0–5.0]	<0.001
Persistent AKI risk factors
Diabetes mellitus	30 (29.4)	14 (22.2)	16 (41.0)	0.043
Chronic kidney disease	18 (17.6)	11 (17.5)	7 (17.9)	0.950
Fluid balance at 24 h,ml/kg	35.2 ± 33.7	22.8 ± 22.6	45.6 ± 44.8	0.029
Use of diuretics at 24 h	7 (6.9)	5 (7.9)	2 (5.1)	0.705
Nephrotoxic agents	20 (19.6)	9 (14.3)	11 (28.2)	0.085
Renal RI	0.67 ± 0.06	0.66 ± 0.05	0.70 ± 0.05	0.001
KRT during hospitalization	9 (8.8)	0 (0)	9 (23.1)	<0.001
Length of ICU stay, days	4.3 [2.7–7.3]	4.0 [2.2–7.8]	4.3 [2.7–7.2]	0.608
Death in the ICU	26 (26.0)	8 (25.5)	18 (46.2)	<0.001

Values represent means ± SDs, n (%), or medians [IQR].

IQR: interquartile range; P-AKI: persistent acute kidney injury; MAP: mean arterial pressure; PaO₂/FiO₂: arterial oxygen partial pressure to fractional inspired oxygen; CVP: central venous pressure; APACHE II: Acute Physiology and Chronic Health Evaluation II; SOFA: Sequential Organ Failure Assessment; sCr: serum creatinine; RI: resistive index; KRT: kidney replacement therapy.

Table 2. Logistic regression models for the prediction of persistent AKI.

Variable included	Univariate analysis		Multivariable analysis		Clinical Model 2		Clinical Model 3		Clinical model 4
	OR (95% CI)	p Value	Clinical Model 1		OR (95% CI)	p Value	OR (95% CI)	p Value	OR (95% CI)	p Value
			OR (95% CI)	P value
sCr at inclusion	1.03 (1.01–1.04)	<0.001	1.02 (1.01–1.04)	0.002	1.03 (1.01–1.04)	<0.001	1.03 (1.01–1.04)	0.001	1.03 (1.01–1.04)	<0.001
Nonrenal SOFA score	1.44 (1.22–1.69)	<0.001	1.41 (1.09–1.83)	0.009	1.47 (1.18–1.82)	0.001	1.40 (1.10–1.80)	0.007	1.48 (1.21–1.81)	<0.001
Lactate	1.72 (1.30–2.27)	<0.001	1.41 (0.96–2.08)	0.079	1.44 (0.99–2.10)	0.057	–	–	–	–
CVP	1.10 (0.99–1.20)	0.053	–	–	–	–	–	–	–	–
Fluid balance at 24 h	1.012 (1.00–1.03)	0.021	–	–	1.00 (0.98–1.03)	0.686	1.01 (0.99–1.03)	0.443	–	–
Norepinephrine dose	12.19 (2.54–58.61)	0.002	2.34 (0.26–20.78)	0.446	–	–	3.67 (0.42–30.44)	0.229	–	–

AKI: acute kidney injury; sCr: serum creatinine; SOFA: sequential organ failure assessment; CVP: central venous pressure; OR: odds ratio; CI: confidence interval.

Hosmer Lemeshow goodness of fit for clinical Model 1: χ² = 9.245, df = 8, p = 0.322; Model 2: χ² = 12.57, df = 8, p = 0.128; Model 3: χ² = 14.354, df = 8, p = 0.073; Model 4: χ² = 9.262; df = 8; p = 0.321.

Figure 2. ROC curve reflecting performance of renal resistive index, the clinical model and their combination for predicting persistent AKI Clinical model includes serum creatinine at inclusion and nonrenal Sequential Organ Failure Score (SOFA). RI: resistive index.

Table 3. Performance of renal RI, the clinical model and their combination for predicting persistent AKI.

	Sensitivity (95% CI)	Specificity (95% CI)	PPV (95% CI)	NPV (95% CI)	AUROC (95% CI)	p Value
Renal RI	56.4 (39.6–72.2)	73.0 (60.3–83.4)	56.4 (39.6–72.2)	73.0 (60.3–83.4)	0.699 (0.600–0.786)
Clinical model	79.5 (63.5–90.7)	79.4 (67.3–88.5)	70.5 (54.8–83.2)	86.2 (74.6–93.9)	0.877 (0.797–0.933)	0.0021^a
Clinical model + Renal RI	84.6 (69.5–94.1)	57.1 (44.0–69.5)	55.0 (41.6–67.9)	85.7 (71.5–94.6)	0.877 (0.797–0.934)	0.9749^b

The clinical model includes serum creatinine at inclusion and the nonrenal Sequential Organ Failure Score (SOFA). RI: renal index, AKI: acute kidney injury, AUROC: area under the receiver-operating characteristic curve, CI: confidence interval, PPV: positive predictive value, NPV: negative predictive value.

^aComparison between the AUROC of renal RI and the clinical model.

^bComparison between the AUROC of the clinical model and the clinical model + RRI.

Table 4. Performance of renal RI for predicting persistent AKI in different subgroups.

Subgroup	Sample	Cutoff value	Sensitivity (95% CI)	Specificity (95% CI)	PPV (95% CI)	NPV (95% CI)	AUROC (95% CI)
Presenting AKI at inclusion	58	0.65	76.7 (57.7–90.1)	60.7 (40.6–78.5)	67.6 (49.5–82.6)	70.8 (48.9–87.4)	0.717 (0.583–0.827)
Age ≥ 70 years	58	0.71	45.8 (25.6–67.2)	88.2 (72.5–96.7)	73.3 (44.9–92.2)	69.8 (53.9–82.8)	0.716 (0.583–0.827)
Baseline sCr based on the previous measurement	79	0.65	85.7 (67.3–96.0)	52.9 (38.5–67.1)	50.0 (32.5–64.8)	87.1 (70.2–96.4)	0.711 (0.599–0.808)
Baseline sCr based on the MDRD formula	23	0.69	54.6 (23.4–83.3)	100.0 (73.5–100.0)	100.0 (54.1–100.0)	70.6 (44.0–89.7)	0.682 (0.457–0.858)

RI: renal index; AKI: acute kidney injury; AUROC: area under the receiver operating characteristic curve; CI: confidence interval; PPV: positive predictive value; NPV: negative predictive value; sCr: serum creatinine: MDRD: Modification of Diet Renal Disease.

Data availability statement

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.