In our study, we used differences in renal biomarkers as the primary endpoint in a relatively homogenous group of patients undergoing aortic valve replacement. Compared to other valvular procedures, aortic valve surgery is associated with relatively higher incidence of acute kidney injury [1]. As with the assessment of postoperative myocardial infarction using cardiac enzymes, the correlation between renal dysfunction and changes in renal biomarkers, especially creatinine, has been well validated [2]. Even transient elevations in the postoperative serum creatinine concentrations have been shown to be associated with adverse outcome following cardiac surgery. As this was the first study to address the reno-protective effect of ulinastatin, we tried to avoid the introduction of confounding factors as much as possible. In patients with pre-existing renal dysfunction, however, the concentrations of renal biomarkers would be already increased and diverse, which could act as a major confounder. Thus, to efficiently assess the potential reno-protective effect of ulinastatin using a small sample size, we had excluded patients with pre-existing renal dysfunction. This in turn, however, invariably confronts generalization of the observed results as was commented by Dr. Guillermo Lema.

Notwithstanding the complex relationship between preoperative patient's co-morbid diseases and postoperative renal dysfunction and clinical outcome, we do acknowledge that a further study with a large sample size involving a heterogeneous group of patients would be necessary to draw a more definite conclusion adding value to the literature. We hope that our study would draw many attentions in that regard.