Cardiovascular Journal of Africa: Vol 32 No 6 (NOVEMBER/DECEMBER 2021)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 32, No 6, November/December 2021 AFRICA 309 This knowledge would allow for modifiable risk factors to be mitigated in the peri-operative period. This research study aimed to describe a profile of AKI in adult patients post cardiac surgery on CPB. The primary objective was to identify the profile of a patient who is likely to develop AKI following cardiac surgery. The secondary objectives were to define factors associated with the development of CSA-AKI using logistic regression analysis to describe the relationship between CSA-AKI and in-hospital mortality using a Kaplan– Meier survival curve, and to determine factors associated with mortality with a Cox regression analysis. Methods This was a descriptive, retrospective cohort study. Data were collected from a single centre. The study population consisted of adult patients over the age of 18 years at CMJAH between January 2016 and December 2017 following cardiac surgery on CPB. Patient information was obtained from anaesthetic, intensive care unit (ICU) and perfusionist charts. A total of 482 peri-operative patient data were retrospectively analysed during the study period. Six patients were excluded from the study due to incomplete essential data, which included SCr levels during the study period, age, gender and race/ethnicity. Patients on RRT pre-operatively were also excluded from the study. Fig. 1 represents a flow diagram of the study data. The current consensus for diagnosing and classifying AKI uses the Kidney Disease Improving Global Outcomes (KDIGO) criteria (Table 1). 4,8,12 In this study, the worst renal functional state within seven days post cardiac surgery was used to diagnose AKI and to grade into KDIGO classes. SCr levels were measured by the National Health Laboratory Service (NHLS), a national government laboratory. A rise of 0.3 mg/dl and higher was used to diagnose AKI. Baseline renal function was determined by calculating pre-operative estimated glomerular filtration rate (eGFR) levels using the Modification of Diet in Renal Disease (MDRD) equation. Pre-operative renal function severity was classified into mild, moderate to severe, and renal failure by eGFR levels (Table 1). 13 In-hospital mortality data post surgery were collected. Ethics approval was attained from the Human Research Ethics Committee (Medical), the Graduate Studies Committee of the University of the Witwatersrand, and the National Health Research Committee (Gauteng). This retrospective analysis of patient records did not require informed consent. Patient information was collected by the primary author (GL), and patient confidentiality was preserved by the identification and assignment of numbers to subjects in the data. The principal investigator and the supervisors had access to patient information. Statistical analysis Data were collected on a Microsoft ® Excel spreadsheet. Stata ® 14 (StataCorp.2015, Stata Statistical Software: Release 14. College Station, TX: StataCorp LP) was utilised for data processing and evaluation. Variables are presented as panel data analytics using absolute numbers, percentages, mean (SD), median (IQR) and categories. The occurrence of CSA-AKI on CPB was estimated with an overall 95% confidence interval and p -values less than 0.05 were statistically significant. Logistic regression analysis was used to determine factors associated with CSA-AKI, the relationship between CSA-AKI and mortality was assessed using a Kaplan–Meier survival curve, and factors associated with mortality with a Cox regression analysis. Results Demographic and pre-operative data for 476 patients are presented in Table 2. The total median (IQR) age was 53 (39–62) years. Patients were predominantly male 255 (53%), and the majority were of the African race [245 (52%)]. A total of 135 (28%) patients developed CSA-AKI within seven days following cardiac surgery on CPB (Table 3). These patients were older and predominantly female. Although they presented with significantly lower eGFR and higher SCr levels pre-operatively as a group compared to those without CSA-AKI, 32 (24%) had presented with normal renal function (eGFR levels) on admission. Prolonged CPB time, peri-operative use of extracorporeal membrane oxygenator (ECMO), and intra-aortic balloon pump Exclude patients 6 patients January 2016 – December 2017 Other surgery 43 (9%) Aortic surgery 17 (4%) No AKI 342 (72%) KDIGO 1 96 (20%) Included patients 476 Valve surgery 249 (52%) CABG 167 (35%) AKI 135 (28%) KDIGO 2 23 (5%) KDIGO 3 16 (3%) Fig. 1. A flow chart showing the derivation of the study cohort. CABG, coronary artery bypass graft; CSA-AKI,cardiac surgery-associated acute kidney injury; KDIGO, Kidney Disease Improving Global Outcomes. Table 1. Definitions of diagnostic criteria 5,13,14 Variables Definition AKI An increase in SCr of > 0.3 mg/dl within 48 hours OR an increase in SCr of > 1.5 times baseline known or presumed to have occurred within the prior 7 days OR urine output < 0.5 ml/kg/h for 6 hours eGFR Normal: > 90 ml/min/1.73 m 2 Mild: 60–89 ml/min/1.73 m 2 Moderate to severe: < 60 ml/min/1.73 m 2 Renal failure: < 15 ml/min/1.73 m 2 KDIGO criteria Class 1 Increased SCr 1.5–1.9 times from the baseline OR urine output < 0.5 ml/kg/h for 6–12 hours Class 2 Increased SCr 2.0–2.9 times from baseline OR urine output < 0.5ml/kg/h for ≥ 12 hours Class 3 Increased absolute SCr to > 4.0 mg/dl OR initiation of RRT OR increased SCr 3.0 times from baseline OR 0.3 ml/kg/h for 24 hours OR anuria for 12 hours AKI, acute kidney injury; SCr, serum creatinine; eGFR, estimated glomerular filtration rate; KDIGO, Kidney Disease Improving Global Outcomes.