In this episode, I’ll discuss the optimal urine output cutoff point to identify acute kidney injury in critically Ill patients.
The standard urine output threshold to identify acute kidney injury (AKI) in critically ill patients is 0.5 ml/kg/hr. However, this threshold may be too high.
A group of researchers recently published in the journal Critical Care a derivation and validation study that sought to develop and validate a novel urine output-based AKI classification system that improves mortality prediction and patient stratification.
The authors used a database of over 35,000 patients to develop the model and then used a separate database to validate it.
Three cutoff points for a 6 hour average of urine output were selected to compose the proposed urine output-AKI classification:
Stage 1 (0.2–0.3 mL/kg/h)
Stage 2 (0.1–0.2 mL/kg/h)
Stage 3 (less than 0.1 mL/kg/h)
Using this criterion, there was a significant stepwise increase in hospital mortality with the advancing the UO-AKI stage.
The authors concluded:
The proposed UO-AKI classification enhances mortality prediction and patient stratification in critically ill patients, offering a more accurate and practical approach than the current KDIGO criteria.
Using a 6 hour urine output threshold is a practical measurement that is also simpler than traditional methods. While this study is limited because it had a retrospective design, the fact that the classification was confirmed in a separate cohort of patients is impressive.
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