Adult congenital heart disease: frequency, risk factors and outcomes of acute kidney injury in postoperative period

Abstract

Background

Acute kidney injury (AKI) after surgery for congenital heart disease (CHD) in adults is poorly studied despite being well-recognized as a postoperative complication after cardiac surgery in adults. The primary aim of our study was to determine the frequency of AKI in adults undergoing surgery for CHD. We also aimed to determine risk factors and predictors of AKI in this patient population, and to explore outcomes in terms of duration of mechanical ventilation, intensive care unit (ICU) stay, and hospital stay.

Methods

This retrospective cross-sectional study included all adult patients (18 years) who underwent cardiac surgery with cardiopulmonary bypass for their congenital heart problems from January 2011 to December 2016 in a tertiary-care private hospital.

Results

A total of 166 patients with a mean age of 32.05 ± 12.11 years were included in this study. The postoperative course was complicated by AKI in 29.5% of patients. Thirty-two percent of these patients had moderate-to-severe kidney disease. Two patients (4%) developing AKI required renal replacement therapy in the form of transient hemodialysis. All patients in our study showed complete resolution of AKI, with no mortalities in the postoperative period. On univariable analysis, (Risk adjusted classification for congenital heart surgery-1) RACHS-1 category 2 and 3, aortic valve replacement, preoperative creatinine clearance, ventricular septal defect closure, cardiopulmonary bypass time, aortic cross-clamp time, intra-operative excessive blood loss, intra-operative ionotropic score, and postoperative hypotension were found to be significant predictors for the development of AKI. On age-adjusted multivariable analysis, RACHS-1 category 2 (OR = 3.49; CI = 1.22–9.95) and category 3 (OR = 3.28 = 1.15–9.36), and intra-operative excessive blood loss (OR = 2.9; CI = 1.07–7.85) were significant predictors of AKI development in the postoperative period. Moreover, development of AKI postoperatively was a predictor of a significantly longer cardiac intensive care unit (CICU) stay (OR = 1.21; CI = 1.08–1.37).

Conclusion

We found that preoperative creatinine clearance, ACC time, intraoperative excessive blood loss, and RACHS-1Category 2 and 3 are potential risk factors for postoperative AKI development. Moreover, patients who develop AKI are likely to have a significantly longer CICU stay. Our study has tried to fill the lacunae with regard to AKI in adults undergoing surgery for CHD. However, there is a need for more studies with larger cohorts involving more complex surgeries to truly estimate the incidence and potential risk factors for AKI in this group of patients.

Electronic supplementary material

The online version of this article (10.1007/s12055-020-00926-z) contains supplementary material, which is available to authorized users.

Introduction

Affecting around 1% of newborns, CHD comprise a variety of frequent and lethal malformations which cause significant morbidity and mortality in infants [1]. There is considerable geographical variation in CHD incidence, with Asia reported to have the highest prevalence [2].

Improved diagnosis and treatment of CHD has led to not only more adults being diagnosed with CHD but has also led to substantial improvement in morbidity and mortality [3]. Moreover, there are other reasons for patients seeking medical attention later in life. These include a lack of access to proper healthcare facilities and medical expertise, a lack of proper education, as well as cultural taboos and poor socioeconomic status. This delay in treatment can potentially lead to worse outcomes.

One of the postoperative complications of surgery for CHD is AKI. It is a frequent occurrence with considerable potential to cause severe health problems. AKI is characterized by a reversible increase in the blood concentration of creatinine and nitrogenous waste products, and by the inability of the kidney to regulate fluid and electrolyte homeostasis appropriately [4].

Despite being a well-recognized complication post-cardiac surgery in children, AKI in adults after surgery for CHD is a less-studied complication. The reported incidence of AKI post-surgery for CHD in the pediatric age group ranges from 3% to 40% and is especially common in infants undergoing cardiopulmonary bypass (CPB) [5–7]. In adults with CHD undergoing surgery, studies have reported an incidence of AKI between 5 and 30% [8]. AKI in adults undergoing surgery for CHD has been associated with adverse outcomes including prolonged mechanical ventilation, longer intensive care unit stay, and higher mortality [9]. However, data regarding postoperative AKI incidence in adults with CHD undergoing CPB is scarce [9].

Aims of study

Our primary aim was to determine the frequency of AKI in adults undergoing surgery for CHD. We also aimed to determine the risk factors for AKI in this patient population and the outcomes in terms of duration of mechanical ventilation, ICU stay, hospital stay, and need for renal replacement therapy (RRT) and mortality.

Material and methods

This retrospective cross-sectional study was conducted after getting approval from the institutional Ethics Review Committee. The sampling technique used was non-probability consecutive sampling for all patients fulfilling the inclusion criteria Table 1.

Table 1.

Demographics and clinical characteristics of the participants

Variables	Acute kidney injury (AKI)
	Total	Yes	No	p value
n	166	49	117
Gender				0.051
Male	89 (53.6)	32 (65.3)	57 (49)
Female	77 (46.4)	17 (34.7)	60 (51)
Age (years)	32.05 ± 12.11	34.73 ± 14.44	30.92	0.064
Weight (kg)	58.96 ± 15.31	62.24 ± 15.98	57.59 ± 14.88	0.074
Height (cm)	160.92 ± 9.29	162.39 ± 8.59	160.31 ± 9.53	0.189
BMI (kg/m2)	22.83 ± 5.91	23.69 ± 6.16	22.47 ± 5.79	0.227
Body surface area (m2)	0.22 ± 0.02	0.21 ± 0.03	0.21 ± 0.02	0.024
Previous surgery	10 (6)	2 (4)	8 (7)	0.725
RACH-1 Score				< 0.0001
1	86 (51.8)	15 (30.6)	71 (61)
2	50 (30.1)	18 (36.7)	32 (27.3)
3	30 (18.1)	16 (32.6)	14 (18.1)
CHD type				0.582
Biventricular repair	162 (97.5)	47 (95.9)	115 (98.3)
Single ventricle	4 (2.5)	2 (4.1)	2 (1.7)
Type of cardiac surgery performed
ASD closure	70 (42.2)	11(22.4)	59(50.4)	0.001
VSD closure	22(13.3)	10(20.4)	12(10)
TOF repair	22(13.3)	7(14)	15(13)
AVR	17(10.2)	11(22.4)	6(5)
Other	35(21.1)	10(20.4)	25(21)

Data presented as mean ± SD and n (%)

The Aga Khan University Hospital has one of the largest cardiothoracic programs in the country and manages > 200 patients of all ages with CHD every year. Data was collected from patients’ charts and results of blood tests were accessed through the online patient data system. A structured proforma was used to collect the data which included demographic data, preoperative data, intraoperative data and postoperative data.

The demographic data collected included the patients’ age at surgery, gender, weight, and height on admission. The preoperative data collected included hemoglobin levels, serum creatinine (SCr), use of nephrotoxic drugs/contrast, RACHS-1 score, preoperative diagnosis, and preoperative left ventricular function. The RACHS-1 scoring system classifies patient risk categories according to the procedure they undergo [10].

The intraoperative data was collected from the surgical and anesthesia records and included CPB time, aortic cross clamp (ACC) use, ACC time, intraoperative hypotension, excessive blood loss [11], need for blood transfusion, previous ACC time (if any), and type of cardiac surgery.

The postoperative data included SCr (day 1 to day 3), creatinine clearance, on-arrival hypotension, on-arrival ionotropic score (high ionotropic score ≥ 20) [12], use of nephrotoxic antibiotics (such as Vancomycin or Amikacin), and low cardiac output [13].

The outcomes measured included development of AKI, need for RRT, total days of RRT, AKI resolution, intubation duration, total length of stay in CICU, total length of stay in hospital, sCr at discharge, mortality in CICU, and day of mortality. The use of RRT included both peritoneal dialysis and hemodialysis.

We defined AKI according to the Kidney Disease Improving Global Outcomes (KDIGO) criteria which specified an increase in serum creatinine of ≥ 0.3 mg/dL (≥ 26.5 μmol/L) within 48 h, or an increase in serum creatinine to ≥ 1.5 times baseline, which is known to have or is presumed to have occurred within the last 7 days; or urine output < 0.5 mL/kg/h for 6 h.

Creatinine levels were measured preoperatively, on the first three postoperative mornings and on the last blood chemistry panel before hospital discharge.

Inclusion criteria

All adult patients (⩾ 18 years) who underwent cardiac surgery with CPB for their CHD from January 2011 to December 2016 at Aga Khan University Hospital, and also had preoperative creatinine measurements, were included in this study.

Exclusion criteria

Patients with acquired heart disease, or those who did not have preoperative creatinine measurements, were excluded.

Statistical analysis

SPSS (Statistical Package for Social Sciences version 15.0) was used for data analysis. Descriptive statistics were presented as mean ± SD and n (%) for continuous and categorical variables, respectively. Student t-test and chi-square test were used for the comparison of mean and percentage,s respectively. Univariable and step-wise multivariable logistic regression models were used to establish the relationship between the exposure and risk factors. Variables were included in the multivariable model on the basis of clinical likelihood and significance (p < 0.25) when analyzed in the univariable model. Multivariable analysis, odds ratios (OR), 95% confidence interval (CI), and p values are presented in tables.

Results

Primary end points

A total 166 patients were included in the study. The mean age of patients was 32.05 ± 12.11 years. About 89 (53.6%) patients were males and 77 (46.4%) were females. Table 1 shows the demographics and Table 2 shows the preoperative, intraoperative, and postoperative characteristics of the study population.

Table 2.

Preoperative, Intraoperative, and postoperative characteristics of the participants

Variables	Acute kidney injury (AKI)
	Total	Yes	No	p value
n	166	49	117
Preoperative
Arrhythmia	5(3)	3(6.3)	2(1.7)	0.153
Creatinine (mg/dL)	0.75 ± 0.24	0.73 ± 0.31	0.75 ± 0.2	0.563
Creatinine clearance (mL/min)	116.53 ± 41.2	128.81 ± 46.72	111.39 ± 37.7	0.013
Comorbid diseases	44(26.5)	18(37)	26(22)	0.053
Intraoperative
CPB time (min)	107.18 ± 64.1	129.78 ± 64.73	97.71 ± 61.69	0.003
Aortic cross clamp time (min)	73.36 ± 49.04	88.88 ± 52.51	66.85 ± 46.22	0.008
Hypotension	11(6.6)	3(6)	8(6.8)	0.656
Excessive blood loss	25(15)	14(29)	11(9)	0.002
Acidosis	19(13)	4(8)	15(13)	0.593
Inotrope score	5.95 ± 6.36	7.63 ± 6.93	5.24 ± 5.99	0.027
Urine output (ml/kg/min)	1.74 ± 0.86	1.79 ± 0.93	1.72 ± 0.83	0.654
Renal perfusion pressure	59.89 ± 13.41	59.92 ± 12.57	59.88 ± 13.8	0.983
Postoperative
Hypotension	31(18.6)	15(26.3)	16(15)	0.011
Nephrotoxic drugs	38(23)	13(27)	24(21)	0.344
Creatinine levels (mg/dL)
Day 1	0.84 ± 0.33	1.06 ± 0.43	0.74 ± 0.2	< 0.0001
Day 2	0.88 ± 0.43	1.16 ± 0.65	0.76 ± 0.2	< 0.0001
Day 3	0.81 ± 0.41	1.04 ± 0.63	0.7 ± 0.2	< 0.0001
At Discharge	0.72 ± 0.23	0.79 ± 0.28	0.7 ± 0.21	0.0026
At the Follow up	0.64 ± 0.22	0.72 ± 0.22	0.59 ± 0.21	< 0.0001
Creatinine clearance (ml/min)	96.19 ± 37.41	74.37 ± 31.06	105.41 ± 36.11	< 0.0001
Duration of mechanical ventilation (days)	1.73 ± 1.96	2.2 ± 2.37	1.54 ± 1.73	0.046
Duration of CICU stay (days)	5.67 ± 4	7.63 ± 5.2	4.85 ± 3.04	< 0.0001
Duration of hospital stay (days)	5.22 ± 0.41	8.01 ± 1.14	2.8 ± 0.26	< 0.0001

Data presented as mean ± Sd and n (%)

AKI was seen in 49 (29.5%) patients. Of the 49 patients with postoperative AKI, 33 (67%) patients had KDIGO Stage 1 AKI, 14 (29%) had Stage 2, and 2 (4%) patients developed Stage 3 AKI. Of the 89 male patients, 32 (36%) developed AKI in the postoperative period, as compared to 17 (22.08%) of the 77 females (p = 0.051). The majority of patients (51.8%) were classified as RACHS-1 category 1, while 50 (30.1%) were classified as RACHS-1 category 2 and 30 (18.1%) were classified as RACHS-1 category 3. In the RACHS-1 category 3, 16 (53.3%) patients developed AKI postoperatively (p < 0.0001).

Biventricular repair was done in 161 (97.6%) patients, out of which 47 (29%) developed AKI. Only 4 patients (2.4%) in our study had univentricular repair, out of which 2 patients (50%) developed AKI postoperatively. The mean preoperative SCr in the overall study population was 0.75 ± 0.24 mg/dl, while the mean preoperative SCr was 0.73 ± 0.31 mg/dl in those who developed AKI postoperatively (p = 0.563).Only 44 (26.5%) patients had comorbid diseases along with CHD, out of which 18 (50%) developed AKI postoperatively (p < 0.053). Only 27 (16.3%) patients had mild or moderate left ventricular (LV) dysfunction preoperatively. Out of these patients, 11 (22.4%) developed AKI postoperatively (p = 0.162). None of the patients had severe LV dysfunction preoperatively.

A total of 70 patients (42%) had an atrial septal defect (ASD), with 11 of them developing postoperative AKI (15.7%). These 11 patients had a significantly higher mean age (38 years vs. 32 years; p = 0.04), significantly lower preoperative hemoglobin (11.9 g/dL vs. 13.3 g/dL; p = 0.03), significantly higher CPB time (83.18 min vs. 64.72 min; p = 0.04) and significantly lower urine output intraoperatively (p = 0.002) as compared to those in the ASD group who did not develop AKI.

Aortic valve replacement (AVR) was done in 17 patients (10%), with 11 (64.7%) developing postoperative AKI. In the AVR group, patients with AKI had a higher mean age (47.8 vs. 39.3 years), longer cardiopulmonary bypass time (CBP) time (135.18 vs. 128.7 min), and longer ACC time (99.5 vs. 90.62 min). However, these differences did not reach statistical significance due to the small sample of 17 patients in the AVR group.

Ventricular septal defect (VSD) closure was done in 22 patients (13%), and 10 (45.5%) of them developed AKI postoperatively. Interestingly, patients with postoperative AKI in VSD group had comparatively higher CPB time (168.5 min vs. 131.25 min; p = 0.06) and ACC time (123.1 min vs. 94.08 min; p = 0.06), but both of these parameters had no statistical significance. This could again be due to the smaller sample of VSD patients.

In our study, 22 patients (13%) underwent tetralogy of Fallot (ToF) repair, with 7 patients (32%) developing AKI postoperatively. Other procedures (mitral valve replacement or repair, Glenn shunt, Fontan completion) were done in 35 patients (21%), out of which 10 patients (28.6%) developed AKI postoperatively (p < 0.001). Mean CBP and ACC times were 107.18 ± 64.1 and 73.36 ± 49.04 min, respectively. In patients with postoperative AKI, the mean CBP time was 129.78 ± 64.73 min (p = 0.003), and the mean ACC time was 88.88 ± 52.51 min (p = 0.008).

Out of a total of 11 patients with intraoperative hypotension, 3 (27%) patients developed postoperative AKI (p = 0.999). A total of 25 (15%) patients had excessive blood loss intraoperatively, out of which 14 (56%) patients developed AKI postoperatively (p = 0.002). In our population, 68 (41%) patients required intraoperative blood transfusion, out of which 28 (41%) developed AKI postoperatively (p = 0.01).The overall mean intraoperative ionotropic score was 5.95 ± 6.36, while patients with postoperative AKI had an intraoperative ionotropic score of 7.63 ± 6.93 (p = 0.027). Mean renal perfusion pressure was 59.89 ± 13.41 mmHg, while in patients with postoperative AKI the mean intraoperative renal perfusion pressure was 59.92 ± 12.57 mmHg (p = 0.983).

In the postoperative period, 31 (18.7%) patients developed hypotension, out of which 15 (48%) patients developed AKI (p = 0.009). About 38 (23%) patients were treated with nephrotoxic drugs, out of which 14 (36.8%%) patients developed AKI (p = 0.34). The overall mean ionotropic score in the postoperative period was 4.07 ± 6.17, while inpatients with postoperative AKI the mean ionotropic score in the postoperative period was 5.76 ± 8.69 (p = 0.047). No patient had low cardiac output syndrome or fluid overload in the postoperative period. Mean serum creatinine levels (mg/dl) on postoperative days 1, 2, and 3 were higher in the AKI group, measuring 1.06 ± 0.43 (p < 0.0001), 1.16 ± 0.65 (p < 0.0001), and 1.04 ± 0.63(p < 0.0001), respectively. The mean creatinine clearance in the postoperative period in the AKI group was 74.37 ± 31.06 ml/min (p < 0.0001). About 2 (4%) patients who developed AKI required RRT in the form of hemodialysis. The mean duration of mechanical ventilation, CICU stay and hospital stay in the AKI group were 2.2 ± 2.37 days (p = 0.046), 7.63 ± 5.2 days (p < 0.0001), and 10.8 ± 8 days (p = 0.002), respectively. Mean serum creatinine levels at discharge and follow up in the AKI group were 0.79 ± 0.28 (p = 0.026) mg/dl and 0.21 ± 0.03 (p = 0.0001) mg/dl, respectively. The median length of hospital stay was 7 days (IQR: 2 days) overall and was 8 days (IQR: 4.5 days) in patients with AKI while 6 days (IQR: 1 day) in those without. The median length of CICU stay was 5 days (IQR: 4 days) and was 6 days (IQR: 5 days) in patients who developed AKI, while it was 5 days (IQR: 3 days) in those who did not.

Secondary end points

On univariable analysis, several variables showed an association with the development of AKI postoperatively. These included RACHS-1 Category 2 (p = 0.017) and 3 (p < 0.0001), AVR for either aortic stenosis or aortic insufficiency (p < 0.0001), preoperative creatinine clearance (p = 0.017), VSD closure (p = 0.006), intraoperative CPB time (p = 0.005), ACC time (p = 0.01), intraoperative excessive blood loss (p = 0.003), intraoperative ionotropic score (p = 0.035), and postoperative hypotension (p = 0.011).

Additionally, patients with postoperative AKI had higher serum creatinine level on postoperative day 1 (p < 0.0001), day 2 (p < 0.0001), and day 3 (p < 0.0001), higher levels of creatinine at discharge (p = 0.003), and longer duration of mechanical ventilation (p = 0.035), CICU stay (p < 0.0001), and hospital stay (p < 0.001).

We performed multivariable analysis in a step-wise pattern with and without age adjustment (Table 3). Before age adjustment, our results showed that preoperative creatinine clearance (p = 0.004), ACC time (p = 0.007), and intraoperative excessive blood loss (p = 0.009) were significant predictors of AKI development. After age adjustment, our multivariable analysis showed that RACHS-1 category 2 (p = 0.019) and category 3 (p = 0.026) and intraoperative excessive blood loss (p = 0.036) were significant predictors of AKI development in the postoperative period. Moreover, development of AKI postoperatively was a predictor of a significantly longer CICU stay (p = 0.002). The full results of the univariable and multivariable analysis are shown in the Supplementary Table.

Table 3.

Predictors of acute kidney injury and impact of clinical outcome

Variables	Multivariate model (step wise)			Multivariate model (step wise age adjusted)
	OR	95% CI	P value	OR	95% CI	p value
Gender
Male	–	–	–	–	–	–
Female
Body surface area	–	–	–	–	–	–
RACHS-1 score
1				Ref.
2	–	–	–	3.49	1.22–9.95	0.019
3	–	–	–	3.28	1.15–9.36	0.026
Pre-Op arrhythmia
Yes	–	–	–	–	–	–
No
Pre-Op comorbid diseases
Yes	–	–	–	–	–	–
No	Ref.			Ref.
Pre-Op creatinine clearance (mL/min)	1.01	1–1.02	0.004	1.02	1.01–1.03
Type of cardiac surgery performed
ASD closure/repair
VSD closure/repair	–	–	–	–	–	–
TOF repair	–	–	–	–	–	–
AVR	–	–	–	–	–	–
Other	–	–	–	–	–	–
Intraoperative CPB time (min)	–	–	–	–	–	–
Intraoperative aortic cross clamp time (min)	1.01	1–1.02	0.007	–	–	–
Excessive blood loss
Yes	3.45	1.37–8.71	0.009	2.9	1.07–7.85	0.036
No	Ref.			Ref.
Intraoperative inotrope score	–	–	–	–	–	–
Postoperative hypotension
Yes	–	–	–	–	–	–
No
Creatinine levels (mg/dL)
Postoperative day 1	–	–	–	–	–	–
Postoperative day 2	–	–	–	–	–	–
Postoperative day 3	–	–	–	–	–	–
Postoperative creatinine clearance (ml/min)	–	–	–	–	–	–
Duration of mechanical ventilation postoperative (days)	–	–	–	–	–	–
Duration of CICU stay duration (days)	–	–	–	1.21	1.08–1.37	0.002
Levels of creatinine at discharge (mg/dL)	–	–	–	–	–	–
Levels of creatinine at the follow up (mg/dL)	–	–	–	–	–	–

Discussion

Although AKI following surgery for CHD has been well established in the pediatric population, there is scarce data regarding this complication in adults undergoing surgery for CHD. In our cohort, 29.5%patients had AKI in the postoperative period. However, the majority had a mild degree of renal injury, with only 2 (4%) out of 49 patients who developed AKI postoperatively being treated with hemodialysis transiently. All patients recovered and had normalization of serum creatinine levels within a month of the initial insult. There was no mortality in our study population.

The majority of our patients (82%) were RACHS-1 Category 1 or 2, while 30 (18%) patients were in RACHS-1 Category 3. Out of the patients in the RACHS-1 Category 3 group, 53% developed AKI postoperatively (p < 0.0001).

Dimopoulos et al. had shown in their study that at least 10% of their adult patients with CHD had moderate to severe AKI, and about half had mild disease at baseline [14]. Buelow et al. found that 54% of patients developed Stage 2 and 3 chronic kidney disease (CKD) several years after ToF palliation [15]. Kwiatkowski et al. reported that 24% of their patients had preoperative renal injury [9]. In our study, all the patients had normal renal function preoperatively.

Kwiatkowski et al. [9] reported an incidence of 36% in their cohort, and similar results were reported by Buelow et al. [16] and Haase et al. (17) in adult patients undergoing cardiac surgery. In our study, 29.5% patient developed AKI the postoperative period. This could be because the majority of our patients were in RACHS-1 Category 1. AKI in the postoperative period has been reported to be associated with increased morbidity and mortality. Sutherland et al. [17] reported that postoperative AKI was associated with increased mortality and prolonged hospital stay. Similar patterns were reported by Zappitelli et al. [18]. Li et al. reported that in pediatric patients developing AKI post-cardiac surgery, 3/4th had resolution of AKI within 48 h [5]. Our study shows similar patterns. Although there was no mortality in our study, patients with postoperative AKI required longer mechanical ventilation (p = 0.046), CICU stay (p < 0.0001) and hospital stay (p < 0.0001) and had higher serum creatinine at discharge and follow-up.

In our study, out of 49 patients who developed AKI, 2 (4%) of them required RRT. This is slightly higher than what is reported by Stellin et al., who reported that 1.5% of their patients required RRT [19]. This could be an outlier because of the smaller sample size of our study. We also found that RACHS-1 Category of 2 or 3, AVR, preoperative creatinine clearance, VSD closure, CPB time, ACC time, intraoperative excessive blood loss, high intraoperative ionotropic score, and postoperative hypotension were associated with development of AKI postoperatively. Prolonged CPB and ACC time are well known and potentially modifiable risk factors for postoperative AKI in patients undergoing surgery for CHD. Our CPB time was comparable to what Karim et al. reported in their study. However, our ACC time was slightly longer. Additionally, 49% of their patients developed AKI in the postoperative period as compared to 29.5% in our cohort [20].

Without adjusting for age, our multivariable analysis showed preoperative creatinine clearance, ACC time and intraoperative excessive blood loss to be significant predictors of AKI development. After age adjustment, our multivariable analysis showed that higher RACHS-1 Category 2 and 3 and excessive intraoperative blood loss were potential risk factors for postoperative AKI development. Our results were slightly different from Kwiatkowski et al. who found that CBP time, LV dysfunction, age ⩾ 35 years, RACHS-1 category, previous arrhythmia, and postoperative use of vancomycin were significant predictors of AKI development [9].

Despite there being attempts to find ways of preventing AKI in the postoperative period, there has been no satisfactory preventive solution found yet. Only the avoidance of potential risk factors, such as nephrotoxic drugs in the perioperative period, has been recommended in various studies. However, the identification of risk factors such as those in our study can be used to exercise more caution to anticipate and prevent development of AKI in high-risk patients. Further studies are needed to clearly identify other existing risk factors for postoperative AKI development, so that by managing these, the incidence of AKI may be lessened. Moreover, given the high incidence of chronic kidney disease in adult patients with CHD [21], the findings of our study also recommend the use of preoperative imaging of the genitourinary tract of this patient population.

Study limitations

Our study has a few limitations, including its limited sample size, its retrospective nature, the majority of patients undergoing relatively simple procedures, younger age of the patients, and the relatively few patients with comorbid disease. In centers with higher number of complex surgeries, the incidence of AKI might be higher. Additionally, studies using decreased urine output or biomarkers for kidney injury have reported higher number of patients with renal injury. Thus, we might have underdiagnosed AKI in our patients, since we used serum creatinine which is less sensitive given the possibility of fluid overload in post-operative period [14, 22]. Moreover, given the retrospective nature of the study, we were also unable to implement a preoperative imaging evaluation of the genitourinary tract of patients to screen for the presence of any chronic kidney disease.

Conclusion

We found that preoperative creatinine clearance, ACC time, intraoperative excessive blood loss, and RACHS-1 Category 2 and 3 are potential risk factors for postoperative AKI development. Moreover, patients who develop AKI are likely to have a significantly longer CICU stay. Our study has tried to fill the lacunae with regard to AKI in adults undergoing surgery for CHD. However, there is a need for more studies with larger cohorts involving more complex surgeries to truly estimate the incidence and potential risk factors for AKI in this group of patients.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Compliance with ethical standards

This retrospective cross-sectional study was conducted after getting approval from the Ethical Review Committee of the Aga Khan University. Since this was a retrospective cross-sectional chart review and did not involve direct patient interaction, patient informed consent was not required.

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

This retrospective study was conducted after getting approval from the institutional research ethics committee and has been performed in accordance with the ethical standards as laid down in the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.

Disclaimer

This research has not been presented or published in a conference or published in any abstract book.

Human and animal rights statement

All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.