We have read the article by Tallarico et al. on perioperative oliguria and congratulate the authors on their well-articulated exploration of this complex topic.1  We would, however, like to highlight some commonly overlooked aspects.

We believe that the diagnostic criteria for acute kidney injury (AKI) might be met in the absence of organic kidney damage by a combination of strong preoperative water retention and additional sodium and fluid build-up resulting from decreased arterial pressure induced by anesthesia.2  Preoperative water conservation usually stems from variations in habitual water intake and can be identified by biomarkers such as elevated urine osmolality or creatinine levels.3  Healthy individuals can be near their maximum renal capacity for urine concentration.4 

Our studies show an inverse correlation between urine flow during surgery and the subsequent rise in postoperative plasma creatinine.2  Patients with high urine creatinine before surgery were unable to further concentrate...

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