Cardiac surgery is unique in using cardiopulmonary bypass in various clinical scenarios. Injury of vital organs is unavoidable in the perioperative period. Acute kidney injury is a consequence of the systemic inflammatory response after bypass, emboli, ischemia, and low cardiac output states, reportedly occurring in 30%-40% of open heart surgeries. Acute kidney injury is associated with increased morbidity, mortality, and cost. Many preventive measures (off-pump procedures, decreased crossclamp time, pulsatile flow, adequate hydration) are taken in the perioperative period to avoid organ injury, but in vain. Traditionally, blood urea, serum creatinine, and creatinine clearance rate were applied for prediction of acute kidney injury. The recent emergence of biomarkers such as neutrophil gelatinase-associated lipocalin, cystatin C, liver-type fatty acid binding protein, interleukin-18, kidney injury molecule-1, and tetrahydrobiopterin have helped in detecting acute kidney injury long before the rise of serum creatinine. These biomarkers can also be used as tools for predicting therapeutic effects in acute kidney injury and for monitoring drug toxicity. This review consolidates the knowledge of biomarkers and their application in acute kidney injury management.

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Objective Renal dysfunction after cardiopulmonary bypass (CBP) ranges from subclinical injury to established renal failure requiring dialysis. The pathophysiology is multifactorial, and recently, hemodilution during CBP has been thought to be an important determinant of postoperative renal injury. In this study, we attempted to assess the independent effect of hemodilution on renal function. We also aimed to identify the optimal hematocrit where hemodilution-induced renal injury is minimal. Methods A prospective observational study was conducted on 200 patients between February 2012 and July 2013. One hundred fifty patients were included in the study group, who were further subdivided on the basis of lowest hemodilution as mild hemodilution (>25%), moderate hemodilution (21%–25%), and severe hemodilution (<21%) categories. The primary outcome of the study was renal outcome measure, which was assessed by comparing the creatinine clearance across the groups. Results The creatinine clearance decreased over a period in all three groups. When compared with mild or moderate hemodilution, the reduction in creatinine clearance was significantly higher in the group with severe hemodilution (P ≤ 0.0001). However, there was no significant difference in creatinine clearance reduction between the mild and moderate hemodilution groups (P = 0.813; 95% confidence interval, −8.41 to 10.68). Conclusions Based on our observations, we would like to propose that a hematocrit of 21% should be considered the critical threshold. Hematocrit below this value of 21% during CBP is associated with the most significant deterioration in renal function.