Volume 91, February 2026, 155336Author links open overlay panel, , , , , , , Section snippetsImpracticality

Although several definitions have been proposed, the current consensus of postoperative AKI (PO-AKI) adopts the KDIGO criteria applied within a 7-day postoperative window [1], whereby a urine output of less than 240 mL over 6 h in a 80 kg patient would meet the threshold for AKI diagnosis. While this consensus also acknowledges the controversies surrounding urine output, an important practical issue is often overlooked: accurate application of this criterion would require continuous bladder

Outcome interpretation

Urine output may also distort the interpretation of perioperative interventions. In the RELIEF trial [5], patients managed with liberal fluid strategies showed lower rates of PO-AKI, but also had higher urine output. This raises the question of whether the observed renal benefit was genuine or merely a transient effect of fluid administration, given that mortality was similar between groups.

Similarly, loop diuretics could appear nephroprotective under current criteria by artificially increasing

Reliability

Serum creatinine, though imperfect, remains the principal surrogate marker for GFR in clinical practice. Equating urine output with creatinine introduces greater inaccuracy. In the postoperative state, usually marked by bleeding, hypotension and inflammation, the body may increase antidiuretic hormone (ADH) secretion to preserve water [6]. Although oliguria may represent an important warning sign of physiological distress, this adaptive reduction in urine output may, in fact, reflect a

Risk factor vs. dysfunction

The authors agree that oliguria should not be underestimated, as its presence represents a risk factor for worse renal outcomes. Nonetheless, in the postoperative setting, it remains unclear whether oliguria should be considered a defining criterion for AKI or interpreted as a risk factor, like hypotension, surgical urgency, illness severity and nephrotoxin exposure

Furthermore, once majority of perioperative oliguria does not translate into GFR reduction when assessed by serum creatinine [4],

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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