Higher body mass index is not a protective risk factor for 28-days mortality in critically ill patients with acute kidney injury undergoing continuous renal replacement therapy

Figures & data

Table 1. The clinical characteristics of patients.

Variables	Underweight (n = 90)	Normal (n = 401)	Overweight (n = 224)	Obesity (n = 405)	p Value
Age, year	63.10 ± 17.48	64.85 ± 13.73	63.94 ± 13.61	61.24 ± 14.59	0.006
Sex (M/F)	53/37	242/159	154/70	238/167	0.082
BMI, kg/m^2	16.70 ± 1.58	21.04 ± 1.22	24.00 ± 0.57	28.20 ± 3.51	<0.001
Myocardial infarction, n (%)	6 (6.67%)	44 (10.97%)	17 (7.59%)	36 (8.89%)	0.400
Congestive heart failure, n (%)	18 (20.00%)	67 (16.71%)	40 (17.86%)	54 (13.33%)	0.268
Cerebrovascular disease, n (%)	8 (8.89%)	45 (11.34%)	25 (11.16%)	35 (8.64%)	0.566
Diabetes mellitus, n (%)	22 (24.72%)	138 (34.41%)	83 (37.05%)	146 (36.05%)	0.187
Hypertension, n (%)	38 (42.22%)	216 (53.87%)	113 (50.45%)	224 (55.31%)	0.125
COPD, n (%)	11 (12.22%)	34 (8.48%)	14 (6.25%)	21 (5.19%)	0.066
MAP, mmHg	76.98 ± 14.99	77.48 ± 14.29	77.35 ± 14.28	77.71 ± 14.46	0.988
WBC, 10^9/L	13.56 ± 11.79	13.60 ± 11.60	14.67 ± 12.58	13.93 ± 10.06	0.572
Hb, g/dL	9.56 ± 2.13	9.67 ± 2.10	9.42 ± 2.26	9.69 ± 2.31	0.403
BUN, mg/dL	60.70 ± 35.26	55.83 ± 28.07	56.79 ± 31.36	54.57 ± 29.82	0.634
Cr, mg/dL	1.03 ± 0.49	1.69 ± 6.10	1.12 ± 0.61	1.31 ± 3.59	0.840
K^+, mmol/L	4.60 ± 1.05	4.62 ± 1.04	4.72 ± 1.13	4.77 ± 1.13	0.389
HCO3-, mmol/L	16.70 ± 5.70	17.68 ± 6.01	16.38 ± 5.75	16.54 ± 5.35	0.023
Phosphate (0 h), mg/dL	5.78 ± 2.90	5.46 ± 2.27	5.86 ± 2.55	5.92 ± 2.27	0.024
Phosphate (24 h), mg/dL	4.43 ± 2.62	4.30 ± 2.23	4.57 ± 2.20	4.74 ± 2.26	0.001
Alb, g/dL	2.48 ± 0.59	2.60 ± 0.58	2.61 ± 0.60	2.65 ± 0.58	0.239
CRP, mg/L	94.63 ± 105.40	122.54 ± 115.61	110.66 ± 105.64	102.6 ± 102.02	0.046
GFR, mL/min	35.22 ± 22.51	32.44 ± 22.51	31.75 ± 22.63	28.86 ± 18.52	0.007
Mechanical ventilation	70 (77.78%)	319 (79.55%)	176 (78.57%)	313 (77.28%)
APACHE II score	25.81 ± 7.55	27.86 ± 7.47	27.64 ± 8.57	26.77 ± 8.13	0.082
SOFA score	11.44 ± 3.50	11.92 ± 3.66	12.10 ± 3.56	12.44 ± 3.43	0.085
CRRT dose, mL/kg/h	38.38 ± 5.72	37.47 ± 4.16	36.71 ± 4.06	35.51 ± 5.26	<0.001
2 h urine at CRRT initiation, mL	60.68 ± 95.17	64.88 ± 87.58	84.09 ± 113.74	73.75 ± 109.15	0.098
AKIN stages
2	14 (15.56%)	122 (30.42%)	67 (29.91%)	90 (22.22%)	0.003
3	76 (84.44%)	279 (69.58%)	157 (70.09%)	315 (77.78%)
CRRT causes
Volume overload, n (%)	10 (11.11%)	53 (13.22%)	32 (14.29%)	57 (14.07%)	0.991
Metabolic acidosis, n (%)	22 (24.44%)	80 (19.95%)	47 (20.98%)	88 (21.73%)
Hyperkalemia, n (%)	5 (5.56%)	20 (4.99%)	12 (5.36%)	19 (4.69%)
Uremia, n (%)	10 (11.11%)	42 (10.47%)	18 (8.04%)	43 (10.62%)
Oliguria, n (%)	25 (27.78%)	111 (27.68%)	56 (25.00%)	98 (24.20%)
Other, n (%)	18 (20.00%)	95 (23.69%)	59 (26.34%)	100 (24.69%)
AKI cause
Sepsis, n (%)	67 (71.28%)	292 (72.82%)	155 (69.20%)	268 (66.17%)	0.269
Nephrotoxin, n (%)	2 (2.13%)	11 (2.74%)	8 (3.57%)	16 (3.95%)
Ischemia, n (%)	3 (3.19%)	36 (8.98%)	22 (9.82%)	36 (8.89%)
Surgery, n (%)	7 (7.45%)	27 (6.73%)	16 (7.14%)	43 (10.62%)
Others, n (%)	15 (15.96%)	35 (8.73%)	23 (10.27%)	42 (10.37%)

Table 2. Univariate analysis.

Variables	Statistics	28-day mortality
Age, year	63.20 ± 14.42	1.00 (1.00, 1.01), 0.788
BMI, kg/m^2	23.78 ± 4.58	0.98 (0.96, 0.99), 0.024
Sex
M	705 (61.63%)	1.00 (Reference)
F	439 (38.37%)	0.94 (0.80, 1.09), 0.396
Myocardial infarction, n (%)	112 (9.79%)	0.89 (0.70, 1.15), 0.379
Congestive heart failure, n (%)	186 (16.26%)	0.77 (0.63, 0.95), 0.016
Cerebrovascular disease, n (%)	114 (10.00%)	0.84 (0.65, 1.08), 0.180
Peripheral vascular disease, n (%)	46 (4.02%)	0.82 (0.56, 1.20), 0.311
Diabetes mellitus, n (%)	398 (34.82%)	0.85 (0.73, 1.00), 0.044
Hypertension, n (%)	601 (52.53%)	0.70 (0.60, 0.81), <0.001
COPD, n (%)	80 (6.99%)	0.81 (0.60, 1.11), 0.192
MAP, mmHg	77.40 ± 14.62	0.98 (0.98, 0.99), <0.001
K^+, mmol/L	4.70 ± 1.10	1.02 (0.95, 1.09), 0.573
HCO3^−, mmol/L	16.91 ± 5.72	0.99 (0.97, 1.00), 0.111
Phosphate (0 h), mg/dL	5.75 ± 2.42	1.06 (1.03, 1.09), <0.001
Phosphate (24 h), mg/dL	4.57 ± 2.32	1.16 (1.13, 1.19), <0.001
Mechanical ventilation	898 (78.57%)	1.83 (1.49, 2.24), <0.001
WBC, 10^9/L	14.13 ± 13.15	1.00 (1.00, 1.00), 0.060
Hb, g/dL	9.63 ± 2.22	0.95 (0.92, 0.98), 0.003
BUN, mg/dL	55.85 ± 29.96	1.00 (1.00, 1.00), 0.135
Cr, mg/dL	2.73 ± 1.62	0.91 (0.87, 0.96), <0.001
Alb, g/dL	2.61 ± 0.58	0.68 (0.60, 0.77), <0.001
CRP, mg/L	110.36 ± 108.05	1.00 (1.00, 1.00), 0.293
GFR, ml/min	31.28 ± 21.17	1.00 (1.00, 1.01), 0.095
CRRT dose, ml/kg/h	36.65 ± 4.80	1.01 (0.99, 1.02), 0.457
2 h urine at CRRT initiation	71.68 ± 102.24	1.00 (1.00, 1.00), <0.001
APACHE II score	27.32 ± 7.97	1.03 (1.02, 1.04), <0.001
SOFA score	12.10 ± 3.55	1.17 (1.14, 1.20), <0.001
AKIN stages
2	298 (26.05%)	1.00 (Reference)
3	846 (73.95%)	1.03 (0.87, 1.21), 0.768
CRRT causes
Volume overload, n (%)	160 (13.99%)	1.00 (Reference)
Metabolic acidosis, n (%)	242 (21.15%)	1.35 (1.04, 1.74), 0.023
Hyperkalemia, n (%)	58 (5.07%)	1.50 (1.03, 2.18), 0.033
Uremia, n (%)	115 (10.05%)	0.90 (0.66, 1.25), 0.538
Oliguria, n (%)	294 (25.70%)	1.02 (0.79, 1.32), 0.862
Other, n (%)	275 (24.04%)	1.26 (0.98, 1.63), 0.072
AKI causes
Sepsis, n (%)	798 (69.76%)	1.00 (Reference)
Nephrotoxin, n (%)	37 (3.23%)	0.93 (0.61, 1.41), 0.723
Ischemia, n (%)	98 (8.57%)	1.06 (0.81, 1.38), 0.667
Surgery, n (%)	94 (8.22%)	0.83 (0.62, 1.11), 0.200
Others, n (%)	117 (10.23%)	1.34 (1.05, 1.70), 0.018

Table 3. Multi-factor cox regression analysis for 28-day mortality.

Exposure	Non-adjusted HR, p Value	Adjusted HR, p Value
Model 1
BMI	0.99 (0.96, 1.03), 0.612	1.00 (0.96, 1.04), 0.987
BMI
18.5–22.99, kg/m^2	1.00 (Reference)	1.00 (Reference)
<18.5, kg/m^2	1.21 (0.88, 1.67), 0.248	1.20 (0.87, 1.66), 0.265
23–24.99, kg/m^2	1.05 (0.83, 1.32), 0.710	1.00 (0.79, 1.27), 0.983
≥25, kg/m^2	1.00 (0.74, 1.37), 0.981	0.96 (0.71, 1.31), 0.806
Model 2
BMI	0.99 (0.96, 1.03), 0.612	1.01 (0.97, 1.04), 0.719
BMI
18.5–22.99, kg/m^2	1.00 (Reference)	1.00 (Reference)
<18.5, kg/m^2	1.21 (0.88, 1.67), 0.248	0.90 (0.57, 1.42), 0.648
23–24.99, kg/m^2	1.05 (0.83, 1.32), 0.710	1.10 (0.80, 1.52), 0.547
≥25, kg/m^2	1.00 (0.74, 1.37), 0.981	1.21 (0.84, 1.74), 0.312
Model 3
BMI	0.99 (0.96, 1.03), 0.612	1.00 (0.96, 1.04), 0.960
BMI
18.5–22.99, kg/m^2	1.00 (Reference)	1.00 (Reference)
<18.5, kg/m^2	1.21 (0.88, 1.67), 0.248	0.87 (0.55, 1.37), 0.543
23–24.99, kg/m^2	1.05 (0.83, 1.32), 0.710	1.18 (0.85, 1.64), 0.313
≥25, kg/m^2	1.00 (0.74, 1.37), 0.981	1.26 (0.87, 1.82), 0.221
Model 4
BMI	0.99 (0.96, 1.03), 0.612	1.00 (0.96, 1.04), 0.931
BMI
18.5–22.99, kg/m^2	1.00 (Reference)	1.00 (Reference)
<18.5, kg/m^2	1.21 (0.88, 1.67), 0.248	1.01 (0.64, 1.61), 0.959
23–24.99, kg/m^2	1.05 (0.83, 1.32), 0.710	1.19 (0.85, 1.66), 0.303
≥25, kg/m^2	1.00 (0.74, 1.37), 0.981	1.17 (0.81, 1.70) ,0.402

Model 1: Adjusted for age, sex, diabetes mellitus, hypertension, COPD, myocardial infarction, congestive heart failure, cerebrovascular disease, AKI cause and CRRT cause.

Model 2: Model 1 and WBC, Alb, CRP, GFR, Hb, BUN, K⁺, HCO3-, Phosphate (0 h) and Phosphate (24 h).

Model 3: Model 2 and Mechanical ventilation at CRRT initiation, CRRT dose, 2 h urine output at CRRT initiation.

Model 4: Model 3 and APACHE II score, SOFA score.

Table 4. Subgroup analysis of multi-factor cox regression analysis for 28-day mortality.

Subgroup variables	Non-adjusted HR, p Value	Adjusted HR, p Value
Diabetes
YES	0.99 (0.96, 1.02), 0.384	0.99 (0.95, 1.02), 0.498
NO	0.99 (0.96, 1.01), 0.236	1.04 (1.00, 1.08), 0.056
Hypertension
YES	0.98 (0.96, 1.01), 0.153	1.01 (0.98, 1.04), 0.614
NO	0.99 (0.97, 1.02), 0.680	1.04 (0.99, 1.09), 0.087
Congestive heart failure
YES	1.00 (0.96, 1.05), 0.829	1.03 (0.98, 1.09), 0.231
NO	0.98 (0.96, 1.00), 0.043	1.00 (0.97, 1.03), 0.885
Sepsis
YES	1.00 (0.97, 1.03), 0.806	0.98 (0.94, 1.02), 0.321
NO	0.98 (0.96, 1.00), 0.0517	1.02 (0.99, 1.05), 0.271
GFR
GFR < 30	0.98 (0.96, 1.01), 0.144	0.98 (0.95, 1.02), 0.365
GFR ≥ 30	0.99 (0.97, 1.02), 0.715	1.04 (1.01, 1.09), 0.049
Mechanical ventilation
YES	0.97 (0.96, 0.99), 0.012	1.01 (0.98, 1.03), 0.653
NO	1.03 (0.98, 1.07), 0.276	1.02 (0.94, 1.11), 0.565
CRRT dose
CRRT dose < 35	1.01 (0.98, 1.04), 0.400	0.99 (0.95, 1.03), 0.701
CRRT dose ≥ 35	0.97 (0.95, 0.99) 0.007	1.03 (1.00, 1.07), 0.077
CRP
CRP < 50	1.00 (0.97, 1.03), 0.857	1.02 (0.99, 1.05), 0.254
50 ≤ CPR < 100	0.98 (0.93, 1.03), 0.396	1.00 (0.93, 1.08), 0.903
CRP ≥ 100	0.98 (0.95, 1.01), 0.183	0.99 (0.95, 1.03), 0.608
SOFA score
SOFA score < 12	1.00 (0.97, 1.03), 0.889	1.02 (0.98, 1.07), 0.344
SOFA score ≥ 12	0.97 (0.95, 0.99), 0.004	1.01 (0.98, 1.04), 0.652

Adjusted variables (without the subgroup analysis variables themselves): age, sex, diabetes mellitus, hypertension, myocardial infarction, cerebrovascular disease, COPD, congestive heart failure, CRRT cause, AKI cause, CRRT dose, WBC, Alb, Hb, CRP, GFR, BUN, K+, HCO₃^–, Phosphate (0 h), Phosphate (24 h), 2 h urine at CRRT initiation, mechanical ventilation at CRRT initiation, APACHE II score and SOFA score.