J Clin Med Res

Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc

Journal website https://www.jocmr.org

Original Article

Volume 000, Number 000, July 2024, pages 000-000

Risk Factors and Outcomes of Acute Kidney Injury After Cardiac Surgery: A Retrospective Observational Single-Center Study

**Table 1.** KDIGO Severity Staging for AKI
Stage	eGFR/serum creatinine criteria	Urine output criteria
eGFR: estimated glomerular filtration rate; KDIGO: Kidney Disease: Improving Global Outcomes.
Stage 1	1.5 - 1.9 times baseline OR ≥ 26.5 µmol/L increase within 48 h	≤ 0.5 mL/kg/h for 6 - 12 h
Stage 2	2 - 2.9 times baseline	≤ 0.5 mL/kg/h ≥ 12 h
Stage 3	Three times baseline OR Increase in serum creatinine ≥ 354 µmol/L OR Initiation of renal replacement therapy (e.g., dialysis)	≤ 0.3 mL/kg/h ≥ 24 h OR Anuria for ≥ 12 h

Table 1. KDIGO Severity Staging for AKI

Stage

eGFR/serum creatinine criteria

Urine output criteria

eGFR: estimated glomerular filtration rate; KDIGO: Kidney Disease: Improving Global Outcomes.

Stage 1

1.5 - 1.9 times baseline
OR
≥ 26.5 µmol/L increase within 48 h

≤ 0.5 mL/kg/h for 6 - 12 h

Stage 2

2 - 2.9 times baseline

≤ 0.5 mL/kg/h ≥ 12 h

Stage 3

Three times baseline
OR
Increase in serum creatinine ≥ 354 µmol/L
OR
Initiation of renal replacement therapy (e.g., dialysis)

≤ 0.3 mL/kg/h ≥ 24 h
OR
Anuria for ≥ 12 h

**Table 2.** Pre-Operative Patient Characteristics
Patient characteristics	Data (% or IQR)
BMI: body mass index; CVI: cerebrovascular insult; IQR: interquartile range.
Gender (male)	142 (85.0)
Age (years)	57 (44 - 64)
BMI	26.3 (23.5 - 30.2)
Diabetes	88 (52.7)
Hypertension	94 (56.3)
Ischemic heart disease	119 (71.3)
Smoking (active or ex-smoker)	54 (32.3)
Previous CVI	11 (6.6)
Congestive heart failure	8 (4.8)
Creatinine (µmol/L)	81 (68 - 102)
Urea (mmol/L)	5.5 (4.3 - 7.4)
Hemoglobin (g/dL)	11.7 (10.0 - 13.2)

Table 2. Pre-Operative Patient Characteristics

Patient characteristics

Data (% or IQR)

BMI: body mass index; CVI: cerebrovascular insult; IQR: interquartile range.

Gender (male)

142 (85.0)

Age (years)

57 (44 - 64)

BMI

26.3 (23.5 - 30.2)

Diabetes

88 (52.7)

Hypertension

94 (56.3)

Ischemic heart disease

119 (71.3)

Smoking (active or ex-smoker)

54 (32.3)

Previous CVI

11 (6.6)

Congestive heart failure

8 (4.8)

Creatinine (µmol/L)

81 (68 - 102)

Urea (mmol/L)

5.5 (4.3 - 7.4)

Hemoglobin (g/dL)

11.7 (10.0 - 13.2)

**Table 3.** Intra- and Post-Operative Patient Characteristics
Patient characteristics	Data (% or IQR)
AKI: acute kidney injury; CABG: coronary artery bypass grafting; CCU: cardiac care unit; CRRT: continuous renal replacement therapy; ICU: intensive care unit; IQR: interquartile range.
Type of surgery
CABG	114 (68.3)
Valve replacement	43 (25.7)
Both	10 (6.0)
Cardiopulmonary bypass duration (min.)	80 (67 - 105)
Cross-clamping time (min.)	55 (42 - 69)
Blood products transfused?	69 (41.3)
AKI post-operatively	46 (27.5)
CRRT/dialysis	4 (2.4)
ICU or CCU stay?	128 (76.6)
Duration (days)	5 (3 - 8)
Post-operative inotropic support	72 (43.1)
Death	5 (3.0)
30-day mortality	4 (2.4)

Table 3. Intra- and Post-Operative Patient Characteristics

Patient characteristics

Data (% or IQR)

AKI: acute kidney injury; CABG: coronary artery bypass grafting; CCU: cardiac care unit; CRRT: continuous renal replacement therapy; ICU: intensive care unit; IQR: interquartile range.

Type of surgery

CABG

114 (68.3)

Valve replacement

43 (25.7)

Both

10 (6.0)

Cardiopulmonary bypass duration (min.)

80 (67 - 105)

Cross-clamping time (min.)

55 (42 - 69)

Blood products transfused?

69 (41.3)

AKI post-operatively

46 (27.5)

CRRT/dialysis

4 (2.4)

ICU or CCU stay?

128 (76.6)

Duration (days)

5 (3 - 8)

Post-operative inotropic support

72 (43.1)

Death

5 (3.0)

30-day mortality

4 (2.4)

**Table 4.** Univariate Comparison Between AKI Versus Non-AKI Patients
Factor predisposing for AKI	AKI (N = 46)	Non-AKI (N = 121)	P-value
AKI: acute kidney injury.
Hemoglobin (g/dL)	9.9 (8.9 - 11.9)	12.0 (10.8 - 13.9)	< 0.0001
Age (years)	65 (40 - 72)	56 (44 - 62)	0.003
Diabetes	21 (45.7)	67 (55.4)	0.300
Hypertension	24 (52.2)	70 (57.9)	0.601
Pre-operative creatinine (µmol/L)	97.5 (77.2 - 127)	77.0 (67.0 - 93.5)	< 0.0001
Pre-operative urea (mmol/L)	7.2 (5.4 - 9.4)	5.2 (4.2 - 6.3)	< 0.0001
Type of surgery			< 0.0001
CABG	25 (54.3)	89 (73.6)
Valve	12 (26.1)	31 (25.6)
Both	9 (19.6)	1 (0.8)
Post-operative inotropes	43 (93.5)	29 (24.0)	< 0.0001
Intra-operative blood products transfused?	32 (69.9)	37 (30.6)	< 0.0001
Cross-clamp time (min)	68.5 (57.3 - 98.0)	47.0 (38.0 - 61.0)	< 0.0001
Cardiopulmonary bypass time (min)	100.5 (80.5 - 119.5)	72.5 (63.0 - 90.0)	< 0.0001

Table 4. Univariate Comparison Between AKI Versus Non-AKI Patients

Factor predisposing for AKI

AKI (N = 46)

Non-AKI (N = 121)

P-value

AKI: acute kidney injury.

Hemoglobin (g/dL)

9.9 (8.9 - 11.9)

12.0 (10.8 - 13.9)

< 0.0001

Age (years)

65 (40 - 72)

56 (44 - 62)

0.003

Diabetes

21 (45.7)

67 (55.4)

0.300

Hypertension

24 (52.2)

70 (57.9)

0.601

Pre-operative creatinine (µmol/L)

97.5 (77.2 - 127)

77.0 (67.0 - 93.5)

< 0.0001

Pre-operative urea (mmol/L)

7.2 (5.4 - 9.4)

5.2 (4.2 - 6.3)

< 0.0001

Type of surgery

< 0.0001

CABG

25 (54.3)

89 (73.6)

Valve

12 (26.1)

31 (25.6)

Both

9 (19.6)

1 (0.8)

Post-operative inotropes

43 (93.5)

29 (24.0)

< 0.0001

Intra-operative blood products transfused?

32 (69.9)

37 (30.6)

< 0.0001

Cross-clamp time (min)

68.5 (57.3 - 98.0)

47.0 (38.0 - 61.0)

< 0.0001

Cardiopulmonary bypass time (min)

100.5 (80.5 - 119.5)

72.5 (63.0 - 90.0)

< 0.0001

**Table 5.** Logistic Regression Analysis for the Development of Post-Operative AKI Based on Significant Results Obtained in Univariate Analysis Detailed in Table 4
Factor predisposing for AKI	OR (95% confidence interval)	P-value
^aType of surgery: CABG, valve repair or both in increasing level of complexity. ^bPost-operative inotropes: odds ratio for NO inotropic support. If YES inotropic support then OR 46.08 (4.136 - 513.3), P = 0.002. *Continuous variables in the analysis. AKI: acute kidney injury; OR: odds ratio.
Hemoglobin (g/dL)*	0.480 (0.279 - 0.826)	0.008
Age (years)*	1.101 (1.021 - 1.186)	0.012
Pre-operative creatinine (µmol/L)*	1.037 (1.000 - 1.076)	0.048
Pre-operative urea (mmol/L)*	0.986 (0.752 - 1.293)	0.921
Type of surgery^a	4.387 (0.797 - 24.149)	0.089
Post-operative inotropes^b	0.022 (0.002 - 0.242)	0.002
Intra-operative blood products transfused?	0.459 (0.069 - 3.047)	0.420
Cross-clamp time (min)*	1.099 (1.009 - 1.197)	0.030
Cardiopulmonary bypass time (min)*	1.039 (0.987 - 1.094)	0.142

Table 5. Logistic Regression Analysis for the Development of Post-Operative AKI Based on Significant Results Obtained in Univariate Analysis Detailed in Table 4

Factor predisposing for AKI

OR (95% confidence interval)

P-value

^aType of surgery: CABG, valve repair or both in increasing level of complexity. ^bPost-operative inotropes: odds ratio for NO inotropic support. If YES inotropic support then OR 46.08 (4.136 - 513.3), P = 0.002. *Continuous variables in the analysis. AKI: acute kidney injury; OR: odds ratio.

Hemoglobin (g/dL)*

0.480 (0.279 - 0.826)

0.008

Age (years)*

1.101 (1.021 - 1.186)

0.012

Pre-operative creatinine (µmol/L)*

1.037 (1.000 - 1.076)

0.048

Pre-operative urea (mmol/L)*

0.986 (0.752 - 1.293)

0.921

Type of surgery^a

4.387 (0.797 - 24.149)

0.089

Post-operative inotropes^b

0.022 (0.002 - 0.242)

0.002

Intra-operative blood products transfused?

0.459 (0.069 - 3.047)

0.420

Cross-clamp time (min)*

1.099 (1.009 - 1.197)

0.030

Cardiopulmonary bypass time (min)*

1.039 (0.987 - 1.094)

0.142