Urine Volume in Acute Kidney Injury: How Much Is Enough?

Figures & data

Table 1  Patients' baseline characteristics: gender, age, serum urea and creatinine (mg/DL), causes of AKI,need for mechanical ventilation, and vasoactives drugs

Group (n)	1 (145)	2 (175)	3 (248)	4 (247)	5 (64)	3+4+5 (559)	Total (879)
Gender
M %	57	58	62	68	83	67	64
F %	43	42	37	32	17	33	36
Age (y)	55 ±18	55 ±19	57 ±19	51 ±19	55 ±17	55 ±19	55 ± 19
U (mg/dL)	210 ± 82	203 ± 76	219 ± 86	204 ± 84	210 ± 102	212 ± 84	210 ± 84
Cr (mg/dL)	6.6 ± 4	5.6 ± 3	5.8 ± 3	5.5 ± 3	4.9 ± 3	5.5 ± 3	5.7 ± 3
ATN (%)	71	73.7‡	66	61	70.3	64	67
PR (%)	7	8	18	21.5	14	19	14.7
HR (%)	6	5.7	3	0.4	1.5	2	3.3
UTO(%)	10││	3.4	3	7	8││	5.4	5.7
VO (%)	5││	0.6	0.4	0.8	0	0.6	1.3
GN/VASC (%)	0§││	8.5	8	4.8	3.1	6	6
AIN (%)	1	0	1.6	4.5	3.1	3	2
MV (%)	76	70	54	42	44	47││	57
VAD (%)	72	69	52	36	31	43││	53

*p < 0.05 vs. female; †p < 0.001 vs. oliguric and non-oliguric, ‡vs. other causes; §p ≤ 0.05 vs. non-oliguric; ││p < 0.001 vs. anuric and oliguric.

Abbreviations: F = female, U = urea, Cr = creatinine, ATN = acute tubular necrosis, VO = vascular obstruction, PR = pre-renal, GN/VASC = glomerulonephritis/vasculitis, HR = hepatorenal, AIN = acute interstitial nephritis, UTO = urinary tract obstruction, MV = mechanical ventilation, VAD = vasoactive drugs.

Table 2  Frequency of dialyzed patients among groups and indication for dialysis: comparison among groups 1 (anuric, urine volume ≤50 mL/24 h), 2 (oliguric, urine volume >50 mL/24 h and <400 mL/24 h), 3 (urine volume ≥400 mL/24 h and ≤1000 mL/24 h), 4 (urine volume >1000 mL/24 h and ≤2000 mL/24 h), and 5 (urine volume >2000 ml)

Group (n)	1 (145)	2 (175)	3 (248)	4 (247)	5 (64)	3 + 4 + 5 (559)	Total (879)
Dialysis (%)	64	62	48	34	28	40	48
Uremia (%)	69	68	84	98	78	94	82
HV (%)	87	78	60	44	22││	51	66

*p < 0.001 vs. anuric and oliguric; †p < 0.05 vs. group 3; ‡p < 0.01 vs. group 3; §p < 0.001 vs. non-oliguric; ││p = 0.05 vs. groups 3 and 4.

Abbreviation: HV = hypervolemia.

Table 3  Frequency of hyperkalemia, hyponatremia, acidosis, and infection among groups 1 (anuric, urine volume ≤ 50 mL/24 h),2 (oliguric, urine volume > 50 mL/24 h and < 400 mL/24 h), 3 (urine volume ≥ 400 mL/24 h and ≤ 1000 mL/24 h), 4 (urine volume > 1000 mL/24 h and ≤ 2000 mL/24 h), and 5 (urine volume > 2000 ml)

Group (n)	1 (145)	2 (175)	3 (248)	4 (247)	5 (64)	3 + 4 + 5 (559)	Total (879)
Hyper K	54	45	42	37	30	39	42
Hypo Na	40	30	34	25	17	28	30
Acidosis	54	48	42	38	31	39	43
Infection	79	82	77	78	80	78	79

*p < 0.001 vs. anuric and oliguric; †p = 0.01 vs. anuric; ‡p = 0.01 vs. oliguric; §p = 0.01 vs. non-oliguric.

Abbreviations: Hyper K = hyperkalemia; Hypo Na = hyponatremia; acidosis = metabolic acidosis.

Table 4  Univariate analysis: risk factors for death

Urine volume	n	Death (%)	OR	CI 95%	p
≤ 50	143	83	3.56	2.1–6.1	<0.00001
50 < UV < 400	174	78	2.54	1.6–4.0	<0.00001
400 ≤ UV ≤ 1000	241	59	1.00	—	—
1000 < UV ≤ 2000	243	38	0.46	0.3–0.7	<0.00001
>2000	63	29	0.28	0.2–0.5	<0.00001
Total	864	58	—	—	—
MV	493	83	13.56	9.6–19.2	<0.0000
VAD	461	85	13.76	9.7–19.5	<0.0000
Hyperkalemia	368	61	1.24	0.93–1.65	0.146
Hyponatremia	258	64	1.36	0.99–1.86	0.055
Acidosis	377	61	1.23	0.92–1.64	0.157
Infection	683	63	2.62	1.84–3.73	<0.000001
<65 yrs.	504	55	—	—	—
≥65 yrs.	330	63	1.42	1.05–1.91	0.018

Abbreviations: OR = odds ratio, CI = confidence interval, UV = urine volume mL/24 h, MV = mechanical ventilation, VAD = vasoactive drug.

Table 5  Multivariate (logistic regression): independent riskfactors for death

	Adjusted OR for death	CI 95%	p
UV ≤ 50	1.95	1.06–3.60	0.032
50 < UV < 400	1.76	1.02–3.03	0.042
400 ≤ UV ≤ 1000	1.00	—	—
1000 < UV ≤ 2000	0.50	0.31–0.80	0.004
UV > 2000	0.30	0.14–0.62	<0.001
Uremia	1.64	1.12–2.39	0.010
MV	4.93	3.18–7.65	<0.001
VAD	4.60	2.96–7.15	<0.001

OR = odds ratio, CI = confidence interval, MV = mechanical ventilation, VAD = vasoactive drug, UV = urine volume (mL/24 h).

Table 6  Multivariate (logistic regression): independent risk factors for death in patients > 18 years old

	Adjusted OR for death	CI 95%	p
UV ≤ 50	1.98	1.06–3.67	0.03
50 < UV < 400	1.97	1.1–3.4	0.017
400 ≤ UV ≤ 1000	0.50	—	—
1000 < UV ≤ 2000	0.52	0.33–0.85	0.08
UV > 2000	0.28	0.14–0.61	0.001
Hypervolemia	1.62	1.0–2.6	0.045
Uremia	1.67	1.14–2.45	0.010
MV	4.96	3.18–7.7	0.000
VAD	3.9	2.5–6.13	0.000

OR = odds ratio, CI = confidence interval, MV = mechanical ventilation, VAD = vasoactive drug, UV = urine volume (mL/24 h).