Postoperative oliguria after intermediate and high-risk surgeries in critical care, A cohort analysis

Introduction: Oliguria is commonly used as a cutoff for acute kidney injury (AKI), however, a decrease in urine output is common during surgery and may represent an adaptative response in the perioperative setting rather than a reduction in glomerular filtration rate, leading to a possible overestimation of postoperative AKI incidence. Although this dilemma has been addressed in the intraoperative scenario, the incidence and impact of oliguria in the first postoperative day represents a gap in the current literature. Our main goal is to describe the incidence, risk factors and clinical outcomes related to postoperative oliguria. Methods: This was a retrospective cohort conducted in four intensive care units (ICUs) across two private Brazilian hospitals, analyzing patients admitted after intermediate and high-risk surgeries between January 1, 2018 and December 31, 2022. Results: 1476 patients were included in the final analysis. Overall, 656 (44,5 %) were males, and the median age was 61,7 years. Oliguria was identified in 508 (34,4 %) patients within the first 24 h after surgery. Vasopressor requirement at admission, non-elective procedures, male sex and baseline serum creatinine were higher among oliguric patients. Among oliguric patients, age and basal serum creatine were higher among those who experienced AKI. Although only 12,4 % of oliguric patients developed AKI according to serum creatinine criterion, this incidence was significantly higher than in non-oliguric group (3,6 %), RR 3.42, IC 95 % 2.3-5.1 (p < 0.01). AKI recovery, RRT, ICU and hospital free days, and mortality were similar between the groups. Conclusions: Postoperative oliguria is common after intermediate and high-risk surgical procedures and increases the risk of AKI. However, oliguria was largely unrelated with kidney disfunction measured by serum creatinine (87,6 %), raising doubts on whether diuresis overestimates AKI incidence in the postoperative setting.