Of the 572 patients who were admitted to MICU and CCU, 332 patients (58%) developed AKI. RRT was initiated in 124 patients; however, we excluded 2 patients who received acute peritoneal dialysis. Thus, a total of 122 patients were included as AKI requiring RRT. Mean patient age was 57.4±18.8 years. Among 122 patients, 108 (88.5%) were diagnosed at medical ICU and 14 (11.5%) were diagnosed at CCU. Sepsis was the most common cause of AKI (97 [79.5%]). Of 122 patients, 105 patients (86.1%) underwent CRRT and 17 patients (13.9%) underwent intermittent hemodialysis. Median time from hospital admission to RRT initiation was 2 days (IQR 0–10.8) and median time from AKI onset to RRT initiation was 1 day (IQR 0-1.8). Among 122 patients, 72 patients (59%, 95% confidence interval [CI] 49.7–67.8) did not survived by day 28 and 88 patients (72.1%, 95%CI 63.3–79.9) by day 90 after AKI diagnosis.
The percentages of missing data across 15 variables that were put in the full regression model varied from 0 to 46.7%. The percentages of baseline SCr and serum lactate before RRT were the two most common missing variables, 46.7% and 32.8%, respectively (Table 1 and Table 2).
Table 1
Baseline characteristics of patients with renal replacement therapy by mortality at day 28
Characteristic | Survivors (50) | Non-survivors (72) | P | Missing, n (%) |
Age, mean±SD, years | 55.8 | (19.9) | 58.5 | (18) | | 0.44 | 0 | (0) |
Male sex, n (%) | 27 | (54) | 45 | (62.5) | | 0.35 | 0 | (0) |
Body mass index, mean±SD, kg/m2 | 22.7 | (3.5) | 22.7 | (4.2) | | 0.98 | 31 | (25.4) |
SOFA, mean (SD), points | 10.3 | (3.7) | 13.7 | (4.5) | < | 0.001* | 5 | (4.1) |
APACHE II, mean (SD), points | 25.8 | (8.8) | 33.1 | (11.4) | < | 0.001* | 7 | (5.7) |
Charlson comorbidities index, median (IQR), points | 4 | (3–7) | 5 | (3-6.25) | | 0.29 | 5 | (4.1) |
ICU type, n (%) Medical ICU Cardiac ICU | 43 7 | (86) (14) | 65 7 | (90.3) (9.7) | | 0.47 | 0 | (0) |
Time to RRT, median (IQR), days Hospital admission to RRT ICU admission to RRT AKI to RRT | 1.0 0 1 | (0-7.5) (0–1.00) (0–2) | 2.5 0 0 | (0–11.0) (0-1.25) (0–1) | | 0.38 0.46 0.09 | 0 | (0) |
Mode of RRT CRRT Intermittent hemodialysis | 37 13 | (74) (26) | 68 4 | (94.4) (5.6) | | 0.001* | 0 | (0) |
Etiology of AKI Septic AKI Non-septic AKI | 31 19 | (62) (38) | 66 6 | (91.7) (8.3) | < | 0.001* | 0 | (0) |
Known baseline SCr, n (%) | 22 | (44) | 43 | (59.7) | | 0.09 | | |
Baseline SCr, median (IQR), mg/dL | 1.38 | (0.90–2.18) | 0.9 | (0.65–1.3) | | 0.01* | 57 | (46.7) |
eGFR, mean±SD, mL/min per 1.73 m2 | 60.2 | (34.3) | 83.4 | (39.9) | | 0.02* | 57 | (46.7) |
CKD staging No CKD Stage I Stage II Stage III Stage IV | 2 3 5 7 6 | (8.7) (13) (21.7) (30.4) (26.1) | 9 9 10 12 4 | (20.5) (20.5) (22.7) (27.3) (9.1) | | 0.36 | 55 | (45) |
AKI = acute kidney injury; APACHE = acute physiology, age, chronic health evaluation; CKD = chronic kidney disease; CRRT = continuous renal replacement therapy; eGFR = estimated glomerular filtration rate; ICU = intensive care unit; IQR = interquartile range; RRT = renal replacement therapy; SCr = serum creatinine; SD = standard deviation; SOFA = sequential organ failure assessment. |
* P < 0.05 when compared with survivors |
Table 2
Clinical and laboratory investigations 24 hours before renal replacement therapy
Characteristic | Survivors (50) | Non-survivors (72) | P | Missing, n (%) |
SOFA, median (IQR), points | 11 | (8.5–13) | 13 | (10–17) | | 0.002* | 4 | (3.3) |
Acute respiratory failure, n (%) | 37 | (75.5) | 69 | (95.8) | < | 0.001* | 1 | (0.8) |
Shock, n (%) | 32 | (64) | 67 | (93.1) | < | 0.001* | 0 | (0) |
Vasopressor, n (%) | 30 | (60) | 67 | (93.1) | < | 0.001* | 0 | (0) |
Acute coronary syndrome, n (%) | 6 | (12) | 5 | (6.9) | | 0.36 | 0 | (0) |
Pulmonary edema, n (%) | 9 | (18) | 13 | (18.1) | | 0.99 | 0 | (0) |
Urine output, median (IQR), mL | 280 | (60–982) | 108 | (9-495) | | 0.03* | 17 | (13.9) |
Cumulative fluid balance, median (IQR), mL | 1643 | (362–3714) | 3677 | (1576–7133) | | 0.01* | 19 | (15.6) |
Arterial pH, median (IQR) | 7.34 | (7.29–7.42) | 7.34 | (7.21–7.43) | | 0.45 | 28 | (23) |
Base excess, mean±SD | -8.2 | (7.5) | -9.8 | (9.1) | | 0.40 | 29 | (23.8) |
PaO2/FiO2, median (IQR) | 298 | (198–433) | 183 | (120–351) | | 0.01* | 28 | (23) |
BUN, median (IQR), mg/dL | 79.7 | (53.2-101.5) | 78.3 | (43.8-110.9) | | 0.92 | 4 | (3.3) |
Serum creatinine, median (IQR), mg/dL | 4.8 | (3.4–7.6) | 3.3 | (2.4–4.9) | < | 0.001* | 4 | (3.3) |
Serum bicarbonate, median (IQR), mEq/L | 14.4 | (11.8–17.7) | 13.6 | (10.1–18.9) | | 0.58 | 4 | (3.3) |
Serum potassium, median (IQR), mEq/L | 4.5 | (3.8–5.2) | 4.9 | (4.0-5.8) | | 0.27 | 4 | (3.3) |
Serum albumin, median (IQR), g/dL | 2.4 | (2.2–3.1) | 2.4 | (2.0-2.7) | | 0.06 | 4 | (3.3) |
Serum lactate, median (IQR), mmol/L | 3.5 | (2.1–7.6) | 8.4 | (4.1–15.1) | | 0.01* | 40 | (32.8) |
BUN = blood urea nitrogen; IQR = interquartile range; SD = standard deviation; SOFA = sequential organ failure assessment. |
* P < 0.05 when compared with survivors |
Baseline clinical characteristics between survivors and non-survivors at day 28 after diagnosis of AKI were shown in Table 1. The non-survivors had a significantly higher severity of illness at the day of ICU admission (mean SOFA score 13.7 vs 10.3, P < 0.001; mean APACHE II score 33.1 vs 25.8, P < 0.001) and lower baseline SCr (0.90 [0.65–1.30] vs 1.38 [0.90–2.18], P = 0.01). The non-survivors had a higher prevalence of septic AKI (66 [91.7%] vs 31 [62%], P < 0.001) but had a lower prevalence of renal AKI (14 [19.4%] vs 18 [35%], P = 0.04). In addition, the number of patients requiring CRRT was higher among non-survivors (68 [94.4%] vs 37 [74%], P = 0.001).
Clinical and laboratory investigations at 24 hours before RRT initiation of survivors and non-survivors at day 28 after diagnosis of AKI were shown in Table 2. Compares to the survivors, the non-survivors had a significantly higher SOFA score (13 [10–17] vs 11 [8.5–13], P = 0.002), a significantly lower PaO2/FiO2 (183 [120–351] vs 298 [198–433], P = 0.01), higher rate of acute respiratory failure (69 [95.8%] vs 37 [75.5%], P < 0.001), higher rate of shock requiring vasopressor (67 [93.1] vs 30 [60%], P < 0.001), and a higher serum lactate level (8.4 [4.1–15.1] vs 3.5 [2.1–7.6], P = 0.01). In addition, the non-survivors had a significantly lower SCr before RRT (3.3 [2.4–4.9] vs 4.8 [3.4–7.6], P < 0.001), a significantly lower 24-hours urine volume before RRT (108 [9-495] vs 280 [60–982], P = 0.03) and a significantly higher cumulative fluid balance (3677 [1576–7133] vs 1643 [362–3714], P = 0.01).
Predictors of mortality at day 28
Fifteen variables were studied by multivariable extended Cox model. Because serum lactate was a time-varying covariate; hence, the extended Cox model with Heaviside functions was used to estimate effect of time varying covariate. Predictors associated with mortality at day 28 were shown in Table 3 and Fig. 1. On multivariable analysis, non-survivors at day 28 showed significant association with a lower baseline SCr (hazard ratio [HR] 0.57, 95%CI 0.36-0.90, P = 0.02), a higher SOFA score before RRT (HR 1.08, 95%CI 1.01-1.15, P = 0.03), a higher rate of shock requiring vasopressor (HR 3.04, 95%CI 1.12-8.25, P = 0.03), and serum lactate > 4 mmol/L for survival time < 10 days (HR 2.49, 95%CI 1.17-5.26, P = 0.02). For the measure of discrimination, the Harrell C-statistics for the reduced model was 0.76 (95%CI 0.70-0.82).
Table 3 Factors associated with non-survivors in patients with renal replacement therapy
Variable
|
Univariable analysisa
|
Multivariable analysisb
|
|
HR
|
95% CI
|
P
|
HR
|
95% CI
|
P
|
Baseline serum creatinine, mg/dLc
|
0.52
|
0.32
|
-
|
0.87
|
|
0.01
|
0.57
|
0.36
|
-
|
0.90
|
|
0.02
|
Time from AKI to RRT, daysc
|
0.93
|
0.83
|
-
|
1.03
|
|
0.15
|
|
Not included
|
|
|
Mode of RRT
|
|
|
|
|
|
|
|
|
|
|
|
|
Intermittent hemodialysis
|
1.00
|
Reference
|
|
|
|
Not included
|
|
|
Continuous renal replacement therapy
|
4.25
|
1.55
|
-
|
11.69
|
|
0.005
|
|
Not included
|
|
|
Etiology of AKI
|
|
|
|
|
|
|
|
|
|
|
|
|
Septic AKI
|
4.09
|
1.77
|
-
|
9.45
|
<
|
0.001
|
|
Not included
|
|
|
Clinical and laboratory before RRT 24 hours
|
|
|
|
|
|
|
|
|
|
|
|
|
SOFA score, pointsc
|
1.14
|
1.08
|
-
|
1.22
|
<
|
0.001
|
1.08
|
1.01
|
-
|
1.15
|
|
0.03
|
Acute respiratory failure
|
4.50
|
1.41
|
-
|
14.30
|
|
0.01
|
|
Not included
|
|
|
Shock
|
4.90
|
1.97
|
-
|
12.18
|
<
|
0.001
|
|
Not included
|
|
|
Vasopressor
|
5.55
|
2.23
|
-
|
13.80
|
<
|
0.001
|
3.04
|
1.12
|
-
|
8.25
|
|
0.03
|
Urine output (per 100 mL)
|
0.96
|
0.92
|
-
|
1.00
|
|
0.06
|
|
Not included
|
|
|
Cumulative fluid balance (per 1 L)
|
1.03
|
0.99
|
-
|
1.06
|
|
0.12
|
|
Not included
|
|
|
PaO2/FiO2 (per 10 mm Hg)
|
0.97
|
0.95
|
-
|
0.99
|
|
0.002
|
|
Not included
|
|
|
Serum creatinine, mg/dLc
|
0.81
|
0.72
|
-
|
0.91
|
<
|
0.001
|
|
Not included
|
|
|
Serum albumin, g/dLc
|
0.58
|
0.38
|
-
|
0.89
|
|
0.01
|
|
Not included
|
|
|
Serum lactate > 4 mmol/L (< 10 days survival time)
|
2.97
|
1.51
|
-
|
5.85
|
|
0.002
|
2.49
|
1.17
|
-
|
5.26
|
|
0.02
|
Serum lactate > 4 mmol/L (≥ 10 days survival time)
|
2.11
|
0.66
|
-
|
6.72
|
|
0.21
|
1.31
|
0.47
|
-
|
3.60
|
|
0.60
|
AKI = acute kidney injury; CI = confidence interval; HR = hazard ratio; RRT = renal replacement therapy; SOFA = sequential organ failure assessment.
Harrell C-statistics for multivariable analysis = 0.76 (95%CI 0.70-0.82).
aanalysis from non-imputed data
bPool analysis after multivariable extended Cox regression of 50 imputed data set
cper 1-point increase