Objective: To determine whether a low perioperative minimum urine output target is safe and fluid sparing when compared with the standard target.
Background: 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.
Methods: 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.
Results: 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).
Conclusions: 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.
*Department of Surgery, The University of Auckland and Department of Surgery, North Shore Hospital, Auckland, New Zealand
†Department of Medicine, University of Otago, Christchurch, New Zealand
‡Department of Surgery, University of Otago, Dunedin, New Zealand
§Department of Anaesthesiology and Perioperative Care, North Shore Hospital, Auckland, New Zealand
¶Department of Medicine, North Shore Hospital, Auckland, New Zealand.
Reprints: Mattias Soop, MD, PhD, Department of Surgery, Salford Royal NHS Foundation Trust, Stott Lane, M6 8HD Manchester, UK. E-mail: email@example.com.
Authors’ contributions: JRP, JM, and MS contributed to the conception of the study and searched the published literature. JRP, JWP, JM, ZE, and MS led the study design, although all authors contributed. JRP, SP, and MS performed the primary data collection and assays. MK and JZ provided anaesthetic and renal medicine supervision, respectively. JRP, JWP, SP, and MS conducted the data analysis. All authors contributed equally to interpretation of the data. MS wrote the first draft of the manuscript and figures with all authors contributing equally to revisions.
Funding disclosures: Funded by the Health Research Council of New Zealand Feasibility Study Grant 11/466 (MS, JRP, JWP, JM, MK, JZ, ZE); Health Research Council of New Zealand Clinical Research Training Fellowship 13/031 (JRP); The University of Auckland lectureship (JRP); Maurice and Phyllis Paykel Trust Project Grant (MS); and Awhina Research Grant, Waitemata District Health Board (MS). Abbott Diagnostics New Zealand provided uNGAL assay kits at reduced cost.
Conflicts of interest: ZE has received honoraria from Novartis P/L. The other authors declare to competing interests.