Introduction
AKI stage | Creatinine criteria | Urine output criteria |
---|---|---|
AKI stage I
| Increase of serum creatinine by ≥ 0.3 mg/dl (≥ 26.4 μmol/L) or increase to ≥ 150% – 200% from baseline | Urine output < 0.5 ml/kg/hour for > 6 hours |
AKI stage II
| Increase of serum creatinine to > 200% – 300% from baseline | Urine output < 0.5 ml/kg/hour for > 12 hours |
AKI stage III
| Increase of serum creatinine to > 300% from baseline or serum creatinine ≥ 4.0 mg/dl (≥ 354 μmol/L) after a rise of at least 44 μmol/L or treatment with renal replacement therapy | Urine output < 0.3 ml/kg/hour for > 24 hours or anuria for 12 hours |
Materials and methods
Study population
Data analysis
Statistical analysis
Results
Incidence of AKI and outcome
No AKI n = 14,405 (65.6%) | AKI 1 n = 4259 (19.1%) | AKI II n = 857 (3.8%) | AKI III n = 2782 (12.5%) | AKI (I + II + III) n = 7898 (35.4%) | p AKI vs no AKI | p AKI III vs AKI I | |
---|---|---|---|---|---|---|---|
Age | |||||||
Mean (SD) | 60.5 (16.56) | 62.1 (15.93) | 60.4 (16.55) | 61.1 (15.66) | 61.5 (15.91) | < 0.0001 | 0.089 |
Range | 16 to 99 | 16 to 95 | 16 to 92 | 16 to 90 | 16 to 95 | ||
APACHE II score at admission to ICU
| |||||||
Median | 13 | 16 | 17 | 21 | 18 | < 0.0001 | < 0.0001 |
Range | 0 to 49 | 0 to 44 | 3 to 39 | 1 to 52 | 0 to 52 | ||
SOFA score on admission to ICU
| |||||||
Median | 5 | 7 | 7 | 9 | 7 | < 0.0001 | < 0.0001 |
Range | 0 to 21 | 0 to 18 | 2 to 19 | 0 to 22 | 0 to 22 | ||
Number of associated failed organs at admission to ICU*
| |||||||
Median | 0 | 1 | 1 | 1 | 1 | < 0.0001 | < 0.0001 |
Range | 0 to 6 | 0 to 5 | 0 to 5 | 0 to 6 | 0 to 6 | ||
Maximum number of associated failed organ systems*
| |||||||
Median | 1 | 1 | 2 | 2 | 2 | < 0.0001 | < 0.0001 |
Range | 0 to 6 | 0 to 5 | 0 to 6 | 0 to 6 | 0 to 6 | ||
Mechanical ventilation
| |||||||
Number of patients | 8379 (58.2%) | 3441 (80.8%) | 696 (81.2%) | 2416 (86.8%) | 6553 (82.97%) | < 0.0001 | < 0.0001 |
Outcome
| |||||||
ICU mortality | 1548 (10.7%) | 856 (20.1%) | 222 (25.9%) | 1379 (49.6%) | 2457 (31.1%) | < 0.0001 | < 0.0001 |
Hospital mortality | 2438 (16.9%) | 1272 (29.9%) | 307 (35.8%) | 1610 (57.9%) | 3189 (40.4%) | < 0.0001 | < 0.0001 |
Length of stay in ICU (days): ICU survivors
| |||||||
Median | 2 | 6 | 7 | 9 | 7 | < 0.0001 | < 0.0001 |
Range | (2 to 55) | (3 to 109) | (3 to 112) | (1 to 270) | (1 to 270) | ||
Length of stay in ICU (days): ICU non-survivors
| |||||||
Median | 2 | 7 | 7 | 8 | 7 | < 0.0001 | < 0.0001 |
Range | (2 to 64) | (3 to 73) | (3 to 54) | (1 to 110) | (1 to 110) | ||
Timing of AKI in ICU
| |||||||
First 48 hours | - | 3529 (82.9%) | 558 (65.1%) | 2075 (74.6%) | 6162 (78.0%) | ||
Day 3 to 5 | - | 424 (9.96%) | 120 (14.0%) | 332 (11.9%) | 876 (11.1%) | ||
Day 6 to 9 | - | 193 (4.5%) | 68 (7.9%) | 207 (7.4%) | 468 (5.9%) | ||
Day 10 – 14 | - | 73 (1.7%) | 49 (5.7%) | 99 (3.6%) | 221 (2.8%) | ||
Day 15 – 19 | - | 20 (0.5%) | 20 (2.3%) | 31 (1.1%) | 71 (0.9%) | ||
> 19th day | - | 20 (0.5%) | 42 (4.9%) | 38 (1.4%) | 100 (1.3%) |
Impact of confounding factors
Factor | AKI III on RRT (n = 1847) | AKI III without RRT (n = 935) | p |
---|---|---|---|
Male gender
| 1242 (67.2%) | 660 (70.6%) | 0.08 |
Age
| |||
Mean (SD) | 60.09 (15.68) | 63.14 (15.42) | 0.28 |
APACHE II on admission to ICU
| |||
Median (range) | 22 (1 to 52) | 19 (2 to 46) | < 0.0001 |
Mean (SD) | 22.92 (7.80) | 19.84 (6.63) | |
SOFA score on admission to ICU
| |||
Median (range) | 10 (0 to 22) | 7 (0 to 17) | 0.0063 |
Mean (SD) | 10.23 (3.18) | 7.61 (2.96) | |
Organ failure on admission to ICU*
| |||
Median (range) | 2 (0 to 6) | 1 (0 to 4) | < 0.0001 |
Mean (SD) | 1.72 (1.20) | 1.11 (0.95) | |
Maximum organ failure during ICU*
| |||
Median (range) | 2 (0 to 6) | 2 (0 to 6) | < 0.0001 |
Mean (SD) | 2.27 (1.17) | 1.67 (0.97) | |
Mechanical ventilation
| 1687 (91.3%) | 729 (77.97%) | < 0.0001 |
Pre-existing chronic illness
| 469 (25.4%) | 238 (25.5%) | 0.97 |
Haemoglobin ≤ 9 g/dl on admission to the ICU
| 496 (26.9%) | 193 (20.6%) | 0.0004 |
Cardiac surgery
| 236 (12.8%) | 95 (10.2%) | 0.051 |
Mortality
| |||
ICU mortality | 999 (54.1%) | 380 (40.6%) | < 0.0001 |
Hospital mortality | 1138 (61.6%) | 472 (50.5%) | < 0.0001 |
Characteristics | ICU Survivors (n = 18,298) | ICU Non-survivors (n = 4005) | Odds ratio (95% CI) | p | ||
---|---|---|---|---|---|---|
n | % | N | % | |||
Male gender | 11,265 | 61.6 | 2441 | 60.9 | 0.97 (0.91 to 1.05) | 0.48 |
Mean age in years (95% CI) | 60.3 (60.1 to 60.6) | 63.5 (63.0 to 63.95) | < 0.0001 | |||
Median APACHE II score at admission to ICU (range) | 13 (0 to 49) | 21 (0 to 52) | < 0.0001 | |||
Median SOFA score on admission to ICU (range) | 5 (0 to 20) | 8 (0 to 22) | < 0.0001 | |||
Degree of maximum renal dysfunction
| ||||||
No AKI | 12,857 | 70.3 | 1,548 | 38.7 | 0.55 (0.53 to 0.57) | < 0.0001 |
AKI I | 3403 | 18.6 | 856 | 21.4 | 1.15 (1.08 to 1.23) | < 0.0001 |
AKI II | 635 | 3.5 | 222 | 5.5 | 1.60 (1.38 to 1.85) | < 0.0001 |
AKI III | 1403 | 7.7 | 1379 | 34.4 | 4.49 (4.20 to 4.80) | < 0.0001 |
Type of admission
| ||||||
Non-surgical | 9236 | 50.5 | 2873 | 71.7 | 2.49 (2.31 to 2.68) | < 0.0001 |
Elective surgery | 6328 | 34.6 | 477 | 11.9 | 0.26 (0.23 to 0.28) | < 0.0001 |
Emergency surgery | 2734 | 14.9 | 655 | 16.4 | 1.11 (1.01 to 1.22) | 0.026 |
Source of admission
| ||||||
Operating room | 8561 | 46.8 | 1072 | 26.8 | ||
Emergency room | 3413 | 18.7 | 750 | 18.7 | ||
Ward (including HDU) | 3845 | 21.0 | 1574 | 39.3 | ||
Hospital transfers | 1894 | 10.4 | 531 | 13.3 | ||
Recovery room | 543 | 3.0 | 62 | 1.5 | ||
Other | 42 | 0.2 | 16 | 0.4 | ||
Chronic end-stage diseases
| ||||||
Present | 3225 | 17.6 | 1,148 | 28.7 | 1.88 (1.74 to 2.03) | < 0.0001 |
Haemoglobin on admission to ICU
| ||||||
Haemoglobin ≥ 9 g/dl | 15,846 | 86.6 | 3238 | 80.8 | ||
Haemoglobin < 9 g/dl | 2452 | 13.4 | 767 | 19.2 | 1.53 (1.40 to 1.67) | < 0.0001 |
Cardiac surgery *
| ||||||
Admission post cardiac surgery | 2507 | 13.7 | 244 | 6.1 | 0.41 (0.36 to 0.47) | < 0.0001 |
Mechanical ventilation
| ||||||
Ventilated | 11,274 | 61.6 | 3658 | 91.3 | 6.57 (5.86 to 7.36) | < 0.0001 |
Renal replacement therapy
| ||||||
RRT for AKI | 848 | 4.6 | 999 | 24.9 | 5.38 (4.94 to 5.86) | < 0.0001 |
Number of failed organs on day of admission to ICU
| ||||||
0 failed organ | 9210 | 50.3 | 704 | 17.6 | 0.21 (0.19 to 0.23) | < 0.0001 |
1 failed organ | 6561 | 35.9 | 1455 | 36.3 | 1.02 (0.95 to 1.10) | 0.58 |
2 failed organs | 2068 | 11.3 | 1164 | 29.1 | 3.22 (2.96 to 3.49) | < 0.0001 |
≥ 3 failed organs | 459 | 2.5 | 682 | 17.0 | 7.98 (7.05 to 9.03) | < 0.0001 |
Maximum number of associated organ failures during entire ICU stay (including AKI)
| ||||||
0 failed organ | 5653 | 30.9 | 96 | 2.4 | 0.05 (0.04 to 0.07) | < 0.0001 |
1 failed organ | 6110 | 33.4 | 459 | 11.5 | 0.26 (0.23 to 0.29) | < 0.0001 |
2 failed organs | 4053 | 22.1 | 993 | 24.8 | 1.16 (1.07 to 1.26) | 0.0003 |
3 failed organs | 1933 | 10.6 | 1350 | 33.7 | 4.31 (3.97 to 4.67) | < 0.0001 |
> 3 failed organs | 549 | 3.0 | 1107 | 27.6 | 12.35 (11.07 to 13.78) | < 0.0001 |
Multivariate analysis
Variables | B | p | OR | 95% CI |
---|---|---|---|---|
Admission post cardiac surgery | -0.567 | 0.000 | 0.567 | 0.47 to 0.69 |
RRT for AKI | -0.202 | 0.039 | 0.817 | 0.674 to 0.99 |
Age | 0.024 | 0.000 | 1.025 | 1.02 to 1.03 |
SOFA score on admission to ICU | 0.104 | 0.000 | 1.109 | 1.09 to 1.13 |
Pre-existing chronic diseases | 0.499 | 0.000 | 1.647 | 1.49 to 1.82 |
Renal function | ||||
No AKI | ||||
AKI I | - 0.024 | 0.000 | 0.82 | 0.73 to 0.91 |
AKI II | 0.051 | 0.59 | 1.05 | 0.87 to 1.27 |
AKI III | 0.820 | 0.000 | 2.27 | 1.92 to 2.69 |
Admission after emergency surgery | 0.846 | 0.000 | 2.329 | 1.997 to 2.72 |
Maximum number of failed organ systems in ICU | 1.028 | 0.000 | 2.795 | 2.66 to 2.94 |
Ventilation | 1.040 | 0.000 | 2.828 | 2.48 to 3.23 |
Non-surgical admission | 1.273 | 0.000 | 3.572 | 3.12 to 4.09 |
Constant | -5.589 | 0.000 | 0.004 |
Additional factors
Timing and progression of AKI
AKI progression | Number of patients | ICU mortality | p |
---|---|---|---|
AKI I (n = 4259) | |||
with rising creatinine values | 1995 (46.8%) | 522 (26.2%) | < 0.0001 |
with falling creatinine values | 2264 (53.2%) | 334 (14.8%) | |
AKI II (n = 857) | |||
with rising creatinine values | 439 (51.2%) | 157 (35.8%) | < 0.0001 |
with falling creatinine values | 418 (48.8%) | 65 (15.6%) | |
AKI III (n = 2782) | |||
with rising creatinine values | 639 (23%) | 318 (49.8%) | < 0.0001 |
with falling creatinine values | 296 (10.6%) | 62 (20.9%) | |
AKI III based on RRT criteria | 1847 (66.4%) | 999 (54.1%) | |
AKI I/AKI II progressing to AKI III | 1664 (59.8%) | 796 (47.8%) | p = 0.029 |
AKI III without prior AKI I/AKI II | 1118 (40.2%) | 583 (46.2%) |
Impact of RRT as a criterion for AKI III
Discussion
Conclusion
Key messages
-
There is a correlation between the newly proposed classification for AKI and outcome in the ICU but only AKI III was an independent risk factor for ICU mortality.
-
In a multivariate analysis, non-surgical admission, mechanical ventilation, maximum number of associated organ failure, admission after emergency surgery and AKI III were the strongest independent risk factors for ICU mortality.
-
The introduction of a 48-hour window for the diagnosis of AKI may miss patients with a slow but progressive acute decline in renal function.
-
RRT as a criterion for AKI III may have a confounding effect on the predictive power of the AKI classification as a whole.