Which of the following indicates a significant decrease in urine output warranting RRT activation?

A urine output of less than 30 ml per hour is a critical indicator warranting the activation of renal replacement therapy (RRT). This threshold is often used in clinical settings as a sign of acute kidney injury (AKI) or severe impairment in renal function. A sustained urine output below this level suggests the kidneys are not adequately filtering waste products, which can lead to a buildup of toxins and other complications in the body.

While other options may indicate varying degrees of urine output, they do not meet the specific criteria used to identify significant renal impairment that necessitates immediate intervention. It's essential for healthcare professionals to monitor urine output closely as it provides vital information about a patient's fluid status and kidney function.