INTRODUCTION: Acute kidney injury (AKI) after trauma is common and associated with poor outcomes. Both inadequate resuscitation and excess fluid administration increase incidence and duration of AKI. We hypothesized that adding ultrasound (US) assessments of inferior vena cava diameter and collapsibility index to usual care would result in shorter AKI duration. METHODS: The Guidance of Ultrasound in Critical Illness to Direct Euvolemia (GUIDE) trial was a sequential, cluster-randomized, crossover comparative effectiveness trial designed to account for care team clusters. ICU teams were randomized to usual care with or without the addition of 24 hours of serial inferior vena cava diameter and inferior vena cava diameter and collapsibility index measurements from September 2019 to June 2020. The primary outcome was AKI duration. Univariate and multivariate analyses were performed. RESULTS: Of 411 patients, 222 were randomized to the US group. Demographics were similar between groups. Patients had a median Injury Severity Score of 26 (interquartile range 16 to 34) and a median age of 38 (interquartile range 26 to 60). The incidence of AKI was similar between groups (US 54% vs usual care 58%, p = 0.46), and the median duration of AKI was 1 day in both groups (interquartile range 0 to 2, p = 0.34). Fluid balances were similar at 24 hours; however, at 48 hours, patients in the US group had a higher fluid balance (Figure). Other complications and mortality were similar between groups.FigureCONCLUSION: This comparative effectiveness trial demonstrated that addition of inferior vena cava diameter and inferior vena cava diameter and collapsibility index assessments to routine care did not affect the duration of AKI but increased patients’ fluid balance at 48 hours. Routine application of US assessments of fluid status in severely injured trauma patients is not recommended.