Low Versus Standard Urine Output Targets in Patients Undergoing Major Abdominal Surgery: A Randomized Noninferiority Trial.

Abstract

To determine whether a low perioperative minimum urine output target is safe and fluid sparing when compared with the standard target. A minimum hourly urine output of 0.5 mL/kg is a key target guiding perioperative fluid therapy. Few data support this standard practice, which may contribute to perioperative fluid overloading. We randomized patients without significant risk factors for acute kidney injury undergoing elective colectomy to a minimum urine output target of 0.2 mL/kg/h (low group) or 0.5 mL/kg/h (standard group) from induction of anesthesia until 8 AM 2 days after surgery. Maintenance fluids were standardized and additional fluids administered to achieve the targets. Primary outcome was noninferiority for urine neutrophil gelatinase-associated lipocalin on the day after surgery. Between November 21, 2011 and July 11, 2013, 40 participants completed the study. The low group received 3170 mL (95% confidence interval 2380-3960) intravenous fluids versus 5490 mL (95% confidence interval 4570-6410) in the standard group (P = 0.0004), and was noninferior for neutrophil gelatinase-associated lipocalin [14.7 μg/L (interquartile range 7.60-28.9) vs 18.4 μg/L (interquartile range 8.30-21.2); Pnoninferiority = 0.0011], serum cystatin C (Pnoninferiority < 0.0001), serum creatinine (Pnoninferiority = 0.0004), and measured glomerular filtration (Pnoninferiority = 0.0003). Effective renal plasma flow increased in both groups after surgery, and more in the standard group (Pnoninferiority = 0.125). A perioperative urine output target of 0.2 mL/kg/h is noninferior to the standard target of 0.5 mL/kg/h and results in a large intravenous fluid sparing. This target should be adopted in surgical patients without significant kidney injury risk factors.