Acute kidney injury after cardiac surgery is more than a postoperative rise in creatinine. A new narrative review by Negargar and colleagues describes a continuum that begins with limited renal reserve, develops through overlapping perioperative insults, and may continue as chronic kidney disease and cardiovascular risk after discharge. For perfusion teams, its central message is the importance of maintaining oxygen delivery while limiting the cumulative burden of hemodilution, hemolysis, inflammation, and impaired perfusion.
What This Review Examines
The authors summarize mechanisms, risk assessment, diagnosis, prevention, supportive treatment, and long-term care for cardiac surgery-associated acute kidney injury (CSA-AKI). This is an educational narrative review, not a new clinical trial or a quantitative comparison of treatment strategies.
The paper reports that AKI affects approximately 20–40% of cardiac surgical patients, with renal replacement therapy required in approximately 1–5%. These are broad literature-based estimates rather than results from a single study population. Definitions, baseline kidney function, procedure complexity, and local practice substantially influence the reported frequency.
Why the Kidney Is Vulnerable During Bypass
Renal injury rarely has one cause. Pre-existing chronic kidney disease, diabetes, anemia, heart failure, and older age can reduce the ability to tolerate additional stress. During surgery, low flow, hypotension, ischemia-reperfusion, inflammatory activation, and disturbances of the renal microcirculation may overlap.
Oxygen Delivery and Hemodilution
During cardiopulmonary bypass, adequate pump flow does not by itself establish adequate oxygen delivery. Hemodilution reduces blood oxygen-carrying capacity, while the renal medulla is particularly vulnerable to an imbalance between oxygen supply and demand. The review emphasizes attention to hematocrit, systemic perfusion, and oxygen delivery together rather than relying on an isolated pressure or flow measurement.
Hemolysis, Inflammation, and Operative Complexity
Blood contact with the extracorporeal circuit activates inflammatory pathways. Hemolysis releases free hemoglobin, and microembolic phenomena may further impair renal microcirculation. Longer bypass duration is associated with AKI, but it also reflects surgical complexity, ischemic exposure, instability, and transfusion requirements. That association should not be interpreted as proof that shortening bypass time alone will prevent injury.
The authors also discuss off-pump surgery, circuit improvements, and biocompatible materials. These approaches have different evidence bases and should not be presented as interchangeable or universally proven renal-protection measures.
Recognizing Injury Before the Creatinine Rise
Serum creatinine and urine output remain the core clinical measures. However, perioperative fluid loading and hemodilution can obscure creatinine changes, while diuretics complicate interpretation of urine output. A reassuring single measurement may therefore miss an evolving problem.
The review discusses NGAL, KIM-1, cystatin C, and urinary TIMP-2 × IGFBP7 as potential adjuncts. These markers reflect different aspects of tubular injury, filtration, or cellular stress. Their performance depends on the population, assay, sampling time, and outcome being predicted.
A positive biomarker does not establish that severe AKI will develop or identify one universally effective treatment. Cost, availability, and uncertainty about the best response to an abnormal result remain barriers. Biomarkers should be interpreted alongside the clinical course and conventional monitoring.
Preventing Acute Kidney Injury After Cardiac Surgery
The review favors coordinated care across the entire perioperative period. Its practical themes can be organized around the following priorities:
| Phase | Key priorities discussed in the review |
|---|---|
| Before surgery | Identify baseline renal impairment, review potentially harmful medication exposures, assess anemia and volume status, and recognize recent contrast exposure. |
| During surgery and CPB | Maintain adequate perfusion and oxygen delivery, avoid sustained hypotension and excessive hemodilution, and limit avoidable hemolysis. |
| After surgery | Follow creatinine, urine output, and cumulative fluid balance; evaluate low cardiac output, bleeding, infection, venous congestion, and medication effects. |
| After discharge | Document the AKI episode and arrange reassessment of renal recovery and ongoing cardiovascular and kidney risk. |
Fluid management requires balance. Inadequate intravascular volume can reduce perfusion, while excessive fluid administration may aggravate edema and venous congestion. Similarly, systemic blood pressure must be interpreted with cardiac function and the overall circulation rather than treated as a complete measure of renal perfusion.
The paper discusses several drugs investigated for renal protection but does not establish a universally effective pharmacologic prevention strategy. Medication decisions should distinguish direct toxicity from hemodynamic effects: the authors specifically note that ACE inhibitors and ARBs are not directly nephrotoxic and require individualized perioperative decisions.
When Supportive Care Is Not Enough
Once AKI develops, management centers on identifying reversible contributors and preventing further injury. The review highlights reassessment of volume status, cardiac output, venous congestion, bleeding, sepsis, obstruction, and nephrotoxic exposure.
Severe metabolic or fluid complications may require kidney replacement therapy. Continuous therapy is commonly used when hemodynamic instability makes gradual fluid and solute removal desirable. The review does not support routine accelerated initiation for every patient with a creatinine rise; timing depends on urgent indications and the evolving clinical picture.
Recovery Extends Beyond Hospital Discharge
Apparent improvement in serum creatinine does not necessarily eliminate future risk. The authors describe associations between postoperative AKI and subsequent chronic kidney disease, cardiovascular events, rehospitalization, and mortality. Their broader message is to make renal recovery part of the discharge plan and ensure continuity between the surgical team, primary care, and nephrology when appropriate.
Limitations and Disclosures
This review does not describe a reproducible systematic search, formal study selection process, risk-of-bias assessment, or pooled analysis. Its conclusions combine evidence from heterogeneous populations and study designs. Approximate incidence ranges and biologically plausible mechanisms should therefore be distinguished from direct evidence that a specific intervention improves outcomes.
The source PDF also contains editorial inconsistencies: its accepted date precedes its received date, and one reference is split across entries 33–35. These issues warrant checking the cited primary literature before using individual claims to change a clinical protocol.
The authors declare no conflicts of interest and disclose using ChatGPT for language editing and grammar improvement, with author review and responsibility for the final content. This independently written summary is intended for professional education.
Original Article
Negargar S, Javanshir E, Sadeghi S. Cardiac Surgery-Associated Acute Kidney Injury: A Continuum from Pathophysiological Mechanisms to Prevention, Management, and Long-Term Care. Galen Medical Journal. 2026;15:e4284. doi:10.31661/gmj.v15i.4284.
The source PDF is unchanged. The cover is an AI-generated editorial illustration, not a technical circuit or anatomical reference.
