Indian Pediatr 2015;52: 223-226
Acute Kidney Injury in
Children After Cardiopulmonary Bypass: Risk Factors and Outcome
Sidharth Kumar Sethi, *Maneesh Kumar, *Rajesh Sharma,
*Subeeta Bazaz and Vijay Kher
From Kidney and Urology Institute and *Heart
Institute, Medanta, The Medicity Hospital, Gurgaon, Haryana, India.
Correspondence to: Dr Sidharth Kumar Sethi,
Consultant, Pediatric Nephrology, Kidney and Urology Institute, Medanta,
The Medicity Hospital, Gurgaon, Haryana, India.
Received: March 11, 2014;
Initial review: April 28, 2014;
Accepted: December 24, 2014.
Objective: To determine the
incidence, risk factors and outcomes of acute kidney injury in children
undergoing cardiac surgery for congenital heart disease. Methods:
We enrolled 208 patients undergoing cardiac surgery for congenital heart
disease during January 2012 to March 2013. Acute kidney injury was
defined as per Acute Kidney Injury Network criteria. Results:
Twenty patients had Acute kidney injury; 14 were infants. Age <1 yr,
cardiopulmonary bypass time, prolonged ventilator requirement, pump
failure, sepsis and hematological complications were identified as
independent risk factors for any degree for acute kidney injury. All
patients with acute kidney injury recovered the kidney function at the
time of discharge. Conclusions: Acute kidney injury is common in
children after cardiac surgery, especially in infants.
Keywords: Cardiac surgery, Complications, Intensive care unit.
mortality . The aim of this study was to assess the
incidence of AKI using the Acute Kidney Injury Network (AKIN) criteria
in children undergoing surgery for congenital heart disease, and to find
its risk factors and outcomes.
Acute kidney injury (AKI) is a frequent
complication of pediatric cardiac surgery and negatively effects short
and long term outcomes. Studies report variable (3-42%) incidence of
post- operative AKI with an associated mortality of 20% to 79% [1-5].
AKI requiring dialysis occurs in about 5% of these patients, in whom the
mortality rate approaches 80% . Even minor degrees of postoperative
AKI may increase the risk of morbidity and
The children (age <18 yrs) who were undergoing
cardiac surgery with cardio-pulmonary bypass for congenital heart
disease at the Pediatric Cardiothoracic unit of our hospital from
January 2012 to March 2013 were eligible for inclusion. Exclusion
criteria were: preoperative mechanical ventilation or extra corporeal
life support, use of pre-operative inotropes, and pre-existing renal
Informed consent was taken from all parents prior to
the inclusion in the study. This study was approved by the Research
Ethics Board of the institution.
The demographic variables obtained were: age at
surgery, weight at surgery, and cardiac diagnosis. Intra-operative
information collected included cardio-pulmonary bypass (CPB) time,
evidence of low output syndrome or pump failure. Post-operative
variables included prolonged ventilator requirement, evidence of sepsis,
hematological dysfunction or hepatic dysfunction and requirement of
renal replacement therapy. Any inotropic or chronotropic medications (e.g.,
epinephrine, dopamine, milrinone) were documented by utilizing the
vasoactive inotropic score. Baseline Serum creatinine was obtained
pre-operatively, either in the preoperative clinic (usually within 1 wk
of surgery) or on the day of surgery. Post-operative serum creatinine
was routinely done on arrival to the intensive care unit (day 1) and
daily till discharge. Arterial blood gas was done 4-hourly for the first
48 hrs and then it was done 6-hrly for another 48 hrs. after which it
was done 12-hrly till discharge from the ICU.
The definition and severity of AKI was based on the
AKIN staging system . As peritoneal dialysis is used routinely at our
institution for perioperative fluid and electrolyte management, we did
not use renal replacement therapy as a criterion for AKI. Instead, we
defined the maximum AKI stage on the basis of serum creatinine criteria.
Baseline renal function was defined according to Schwartz formula. We
did not evaluate urine output as a determinant of AKI because 95% of the
patients in our unit receive a diuretic within 12 hours of arriving to
the intensive care unit (ICU), which may limit the reliability of urine
output being a direct indication of innate renal function.
The diagnosis of pump failure or low output syndrome
was made as per criteria laid by Hoffman [9,10]. Hematological
dysfunction was defined as platelet count <80,000/mm3
or a decline of 50% from the highest value recorded over the last 48
hours. Hepatic Dysfunction was defined as Alanine transaminase level
more than twice upper limit of the normal.
Prolonged ventilatory requirement was defined as need for
invasive ventilation for more than 48 hours.
The results were analyzed using SPSS software. We
performed Student’s t test for normally distributed continuous
variables, Mann-Whitney U test for non-normally distributed continuous
variables, and chi-square test for categorical variables. Statistical
significance was defined as a probability value less 0.05. Univariate
logistic analysis was then performed to examine the risk factors for
AKI. Any variable with a probability value less than 0.1 was entered
into a multivariate stepwise logistic regression analysis to analyze
independent predictors for AKI. The following risk factors were included
in the analysis: gender, age group (<1 year, >1 year), body weight (<10
kg, >10 kg), duration of cardiopulmonary bypass, pump failure, prolonged
ionotrope requirement, hepatic dysfunction, hematological complications,
ventilator requirement, and sepsis. Two children who required peritoneal
dialysis for management of fluids post-operatively in view of complex
prolonged surgery and pump failure, in the absence of creatinine or
urine output criterion were excluded from the analysis.
We studied 208 patients (150 boys) who underwent
cardiac surgery for congenital heart disease from January 2012 to March
2013. The mean (SD) age and weight of patients was 66.9 (95.6) months
and 16.3 (16.5) kg, respectively. Mean (SD) CPB time was (38) minutes,
and mean (SD) hospital stay was 11.5(3) days.
The spectrum of surgeries included ventricular septal
defect closure (56), tetralogy of fallot correction (47), arterial
switch operation (29), atrial septal defect closure (18), total
anamolous pulmonary venous connection repair (8), fontan procedure (9),
truncus repair (3), coarctation of aorta repair (3) and others (35). One
patient had Risk Adjustment in Congenital Heart Surgery Surgical
Severity Score (RACHS score) of 1, 148 patients had RACHS score of 2, 48
patients had RACHS score of 3, and 10 patients had RACHS score of 4.
Sepsis developed in 41 (19.7 %) patients. Prolonged
ventilator support was required in 33 (15.9%) patients, and eight
patients developed pump failure during the surgery. Hematological
complications developed in 22 (10.6%) of patients and five (2.4%)
patients died following the surgery.
The mean (SD) baseline renal function, as assessed by
Schwartz formula, was 100.4 (12.3) mL/min/1.73 m2,
and mean (SD) urinary protein/creatinine ratio was 0.11 (0.06).
Twenty patients (9.6%) had AKI (AKI-I 15 patients;
AKI-II 1 patient and AKI-III 4 patients). One patient with stage III AKI
died. In most patients AKI occurred within the first five post-operative
days. Ten patients required peritoneal dialysis. The duration of
peritoneal dialysis ranged from 24 hours to 4 days. All patients with
AKI recovered the kidney function at the time of discharge, with normal
TABLE I Comparison of Intra- and Post-operative Variables in Children With or Without AKI.
*Age <12 mo
*Requirement for prolonged ventilation
*Renal replacement therapy
*CPB time (min)
*Maximum inotrope score
*ICU stay (d)
AKI = Acute kidney injury; *P<0.01; #P=0.01.
The comparison of intra- and post- operative
variables with the incidence of AKI is shown in Table I.
CPB time, age <1yr, pump failure, prolonged ventilator requirement,
sepsis, length of ICU stay, hematological complications and requirement
of renal replacement therapy were more common in children with AKI. On
multivariate logistic regression analysis, young age, CPB time,
prolonged ventilator requirement, pump failure, sepsis and hematological
complications were independently associated with higher odds of AKI (Table
TABLE II Risk Factors for AKI in Study Children
OR (95% CI)
Age (<12 mo)
CPB time (minutes)
Prolonged ventilator requirement
AKI – Acute kidney injury.
All ten patients in the study who required dialysis
were less than 12 months. Age <12 mo. was a strong predictor of
post-operative complications viz. prolonged ventilator
requirement, pump failure, AKI, sepsis, hematological complications, RRT
requirement, and prolonged hospital stay (P<0.001). The mean (SD)
length of ICU stay in children <12 months was 12.6 (3.5) days in
comparison to 10.8 (2.4) days in children >12 months (P<0.001).
We found the incidence of acute kidney injury in
children, following a cardiopulmonary bypass to be 9.6%. Children who
were young, had a prolonged CPB time, prolonged ventilator requirement,
pump failure, sepsis and hematological complications were more likely to
have acute kidney injury. Infancy was a strong predictor of
post-operative complications, including a longer ICU stay and mortality.
The incidence observed in the present study is in
broad agreement to the earlier studies [10,11]. Higher (52-68%)
incidence of cardiac surgery associated AKI (CS-AKI) in the few other
studies [4,12-15] could be due to inclusion of younger children in those
studies. Associations of acute kidney injury with young age, prolonged
bypass time, pump failure, sepsis has been reported previously
[6,11-15]. The increased frequency of post-operative complications
during infancy may be due to an increased risk to reperfusion, oxidative
stress and systemic inflammatory response insults in the setting of
immature kidneys, CPB induced hypothermia, and case complexity of the
There were several limitation in our study, being a
small sized, single center study. We did not evaluate urine output as a
determinant of AKI. We chose to do this because 95% of the patients in
our unit receive a diuretic within 12 hours of arriving to the ICU,
which may limit the reliability of urine output being a direct
indication of innate renal function. We also did not look at proteinuria
and hypertension on follow up in our patients. This shall be a part of
future research in these patients.
We conclude that the risk of AKI is far greater in
infants and young children. Infants with prolonged surgery, prolonged
ventilator requirement, pump failure, sepsis and hematological
complications post-operatively are at highest risk of developing AKI,
and require a longer hospital stay. There is a need for more research on
children post cardiac surgery, and looking at strategies to prevent
Contributors: SKS: concept of study, data
collection, analysis, drafting and revision of manuscript; MK: concept,
design; collection of data; and drafting the manuscript; RS: supervision
of the work; collection of data; and drafting and revision of
manuscript; SB: supervision of the work; collection of data; and
drafting and revision of manuscript;; VK: supervision of the work, data
analysis and revision of manuscript. SKS will act as the guarantor.
Funding: None; Competing interests: None
What This Study Adds?
Children with prolonged cardiac
surgery, prolonged ventilator requirement, pump failure, sepsis
and hematological complications are at highest risk of
developing acute kidney injury and adverse outcomes
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