Studies in Renal Physiology in Elective Major Surgery

Abstract

INTRODUCTION: Acute kidney injury is a common cause of in-hospital morbidity and mortality. However, little is known concerning the non-cardiothoracic, non-vascular, nonurological and non-transplant patient undergoing elective surgery, and their risk of perioperative acute kidney injury. METHODS: A systematic literature review was conducted to identify the incidence of and pertinent modifiable risk factors for the development of perioperative acute kidney injury in this population. A multi-centre case study was undertaken to ascertain the consequences of severe acute kidney injury as defined by the clinical outcome of renal replacement therapy. A retrospective cohort study was performed to ascertain the incidence of and clarify if anecdotal perioperative urine output was a risk factor for the development of acute kidney injury along with the quantity of intravenous fluid used to treat it. These studies will aid the design and implementation of a randomised non-inferiority trial testing the hypothesis that a lower urine output target is as safe as current practice and thus reducing the risk of perioperative fluid excess and its clinical consequences. RESULTS: Acute kidney injury in this population is common at 5.07%. Increasing body mass index and use of perioperative angiotensin converting enzyme inhibitors are modifiable factors that potentially convey an increased risk for its development. Whilst rare, acute kidney injury in its severest form (requiring renal replacement therapy) has a mortality of 26% and amongst survivors, results in a significant reduction in long-term renal function. Whilst acute kidney injury appears to be uncommon, oliguria, as currently defined as ≥0.5ml/kg/h, is common in the general surgical population (84%), but does not appear to be correlated to a change in renal function and results in increased intravenous fluid administration. A lower perioperative urine output target of ≥0.2ml/kg/h is non-inferior to the traditional target of ≥0.5ml/kg/h using uNGAL as a surrogate biomarker of acute kidney injury, and reduces the risk of clinically significant administration of excess intravenous fluid. CONCLUSION: Acute kidney injury is common, and whilst rare, its sequelae are clinically and financially significant. These studies have demonstrated that preoperative optimisation of patient factors can reduce these sequelae. Furthermore, they have shown that much of the intravenous fluid prescribed in the perioperative period is in response to perceived clinically significant low urine outputs. Employing a lower urine output target of ≥0.2ml/kg/h results in fewer patients receiving overhydration and its associated increase in mortality and morbidity without risking renal damage.