Table 1
Key studies on cardiac‑surgery‑associated acute kidney injury (CSA‑AKI) in high‑income and low‑/middle‑income settings.
| STUDY (YEAR) | COUNTRY / REGION | INCOME SETTING | STUDY DESIGN | POPULATION | AKI DEFINITION | AKI INCIDENCE | SEVERE AKI / RRT | AKI‑ASSOCIATED MORTALITY | KEY FINDINGS RELEVANT TO LMIC–HIC CONTRAST |
|---|---|---|---|---|---|---|---|---|---|
| Hobson et al. [4] | United States | HIC | Retrospective cohort | 2,973 adult patients undergoing cardiothoracic surgery | RIFLE (serum creatinine–based) | ~30%–43% (any AKI) | ~1%–2% required RRT | Mortality increased stepwise with AKI severity; long‑term mortality independently higher even after mild AKI | Demonstrates that even in high‑resource settings with universal access to RRT, CSA‑AKI—including mild forms—confers a durable survival disadvantage |
| Thakar et al. [6] | United States (Cleveland Clinic) | HIC | Retrospective cohort (derivation and validation) | 33,217 adults undergoing open‑heart cardiac surgery | Acute renal failure requiring dialysis | ~1% overall (0.5%–22.1% across risk strata) | Dialysis‑requiring AKI (primary outcome) | ~40%–60% in patients requiring RRT | Establishes a high‑resource benchmark: dialysis‑requiring CSA‑AKI is rare but carries extremely high mortality despite early detection and unrestricted RRT access |
| Machado et al. [5] | Brazil | Upper‑middle‑income (LMIC) | Retrospective cohort | 2,804 adults undergoing cardiac surgery | KDIGO (serum creatinine only) | 42% overall | 2% required RRT (~65% of KDIGO stage 3) | 30‑day mortality rose sharply with AKI severity; 55% in KDIGO stage 3 | High AKI incidence with limited RRT use; mortality markedly higher in severe AKI, highlighting vulnerability in resource‑constrained settings |
| Leballo et al. [10] | South Africa | LMIC | Retrospective single‑center cohort | 476 adults undergoing cardiac surgery with cardiopulmonary bypass | KDIGO criteria | 28% overall | ~3% required RRT (subset of KDIGO stage 3) | In‑hospital mortality: 21% with AKI vs 5% without; 44% in KDIGO stage 3 | Demonstrates substantial mortality gradient by AKI severity in an LMIC setting with constrained access to advanced renal support |
| Xie et al. [9] | China | Upper‑middle‑income (LMIC) | Retrospective cohort | 2,575 adults undergoing first cardiac surgery with CPB | KDIGO (serum creatinine only) | 36% overall | 1.2% required RRT | Mortality higher with AKI (2.6% vs 0.9%); RRT strongly associated with death (adjusted HR 18.68) | High AKI incidence with relatively low RRT utilization; mortality escalates dramatically once RRT is required |
Table 2
LMIC‑Specific Health‑System Challenges and Their Clinical Consequences in Cardiac Surgery–Associated Acute Kidney Injury (CSA‑AKI).
| HEALTH‑SYSTEM CHALLENGE (LMIC) | MECHANISM OF IMPACT | CLINICAL CONSEQUENCE IN CSA‑AKI | CONTRAST WITH HIC SETTINGS |
|---|---|---|---|
| Late referral for cardiac surgery | Prolonged exposure to low cardiac output, venous congestion, and neurohormonal activation before surgery | Reduced baseline renal reserve; higher susceptibility to perioperative AKI; advanced AKI at diagnosis | Earlier referral and elective optimisation reduce preoperative renal stress |
| High burden of undiagnosed CKD and comorbidities | Limited primary care screening; poor chronic disease control | AKI occurs on a background of chronic renal vulnerability, accelerating progression to severe stages | Routine CKD detection and optimisation common preoperatively |
| Limited preoperative optimisation | Short preoperative admission windows; lack of multidisciplinary assessment | Inadequate volume, blood pressure, and medication optimisation before CPB | Structured prehabilitation and risk stratification pathways |
| Longer cardiopulmonary bypass times | Case complexity, workflow inefficiencies, limited access to off‑pump techniques | Greater inflammatory burden, renal hypoperfusion, and haemodilution | Shorter CPB duration and goal‑directed perfusion strategies |
| Reduced intraoperative monitoring capacity | Reliance on intermittent haemodynamic measurements; absence of renal/cerebral oximetry | Occult hypotension and renal hypoperfusion go undetected | Continuous invasive monitoring and perfusion‑guided targets |
| Delayed postoperative laboratory testing | Limited lab availability, staffing shortages, batching of samples | AKI recognised at later, less reversible stages | Early creatinine trends and urine output protocols |
| Absence of early AKI biomarkers | Cost and infrastructure constraints | Reliance on late creatinine rise; missed therapeutic window | NGAL, cystatin C used selectively for early detection |
| Limited nephrology availability | Workforce shortages; competing service demands | Delayed specialist input and delayed RRT decision‑making | Early nephrology consultation integrated into ICU care |
| Restricted access to renal replacement therapy (RRT) | Limited dialysis machines; prioritisation pressures; cost barriers | Dialysis‑requiring AKI becomes a high‑mortality phenotype | CRRT readily available; early initiation feasible |
| Predominant use of intermittent haemodialysis | Infrastructure limitations | Poor haemodynamic tolerance in vasoplegic post‑cardiac surgery patients | CRRT preferred for unstable patients |
| Absence of AKI prevention bundles | Lack of protocolised care pathways | Inconsistent fluid, drug, and monitoring practices | Standardised AKI bundles and quality metrics |
| Lack of national cardiac surgery registries | Limited data capture and feedback loops | Under‑recognition of AKI burden; limited quality improvement | Continuous benchmarking and outcome monitoring |