Urine output on ICU entry is associated with hospital mortality in unselected critically ill patients

Urine output (UO) is routinely measured in the intensive care unit (ICU) but its prognostic value remains debated. The study aimed to investigate the association between day 1 UO and hospital mortality. Clinical data were abstracted from the Multiparameter Intelligent Monitoring in Intensive Care II (version 2.6) database. UO was recorded for the first 24 h after ICU entry, and was classified into three categories: UO > 0.5, 0.3-0.5 and a parts per thousand currency sign0.3 ml/kg per hour. The primary endpoint was the hospital mortality. Four models were built to adjust for the hazards ratio of mortality. A total of 21,207 unselected ICU patients including 2,401 non-survivors and 18,806 survivors were included (mortality rate 11.3 %). Mortality rate increased progressively across UO categories: > 0.5 (7.67 %), 0.3-0.5 (11.27 %) and a parts per thousand currency sign0.3 ml/kg/h (18.29 %), and this relationship remained statistically significant after rigorous control of confounding factors with the Cox proportional hazards regression model. With UO > 0.5 as the referent group, the hazards ratios for UO 0.3-0.5 and UO a parts per thousand currency sign0.3 were 1.41 (95 % CI 1.29-1.54) and 1.52 (95 % CI 1.38-1.67), respectively. UO obtained on ICU entry is an independent predictor of mortality irrespective of diuretic use. It would be interesting to examine whether strategies to increase UO would improve clinical outcome.