Intraoperative permissive oliguria – how much is too much?

Abstract

Acute kidney injury (AKI) after general surgery is a serious complication. In abdominal surgery the incidence is around 13%, and it is associated with increased postoperative morbidity, length of hospital stay and a 13-fold increase in the relative risk of inhospital or 30-day mortality. 1 2 Oliguria is one of the oldest markers of AKI, and was historically described by Epheseus and Galen in 100-200 AD. 3 4 By consensus, oliguria is defined as urine output <0.5 ml kg À1 h À1. 5 Perioperative causes of oliguria include intravascular hypovolaemia, prolonged hypotension and reduced perfusion of the kidneys, but also non-renal causes such as release of anti-diuretic hormone (ADH) in response to nausea or pain. In the critical care setting, oliguria is common, and often considered as an early marker of renal injury, preceding a rise in creatinine. 6-8 Multiple studies in critical care patients with AKI demonstrated an association between oliguria and mortality. 9 10 Recently, Teixeira and colleagues 11 confirmed in an observational multicentre study of 601 critical care patients that oliguria per se was independently associated with mortality. In contrast to oliguria in the critical care setting, intraoperative oliguria appears to be less reliable in predicting AKI as was already suggested 30 yr ago in patients undergoing abdominal aortic surgery. 12 13 More recent studies indicated that oliguria during general anaesthesia was a result of reduced clearance and slower distribution of fluids administered intraoperatively and therefore potentially unrelated to renal function. 14 15 Intraoperatively, urine output is not only influenced by haemodynamics but also sympathetic tone, aldosterone and ADH levels. Increased intra-abdominal pressure independent of fluid status and blood pressure might also contribute, as shown by two studies in laparoscopic surgery. 16 17 A large retrospective study in 15-100 patients undergoing abdominal surgery demonstrated that intraoperative oliguria did not predict postoperative AKI. 18 Based on existing studies, one can conclude that the nature and impact of intraoperative oliguria or 'permissive oliguria' in anaesthetised patients undergoing elective surgery depends on patient characteristics and clinical conditions, and may not necessarily be associated with postoperative AKI. 19 20

Intraoperative Oliguria with Decreased SvO2 Predicts Acute Kidney Injury after Living Donor Liver Transplantation

“…Several studies have attempted to derive urine output thresholds that identify AKI in surgical patients [30,31,32]. Using a methodology that was similar to ours, one retrospective study in cardiac surgical patients undergoing cardiopulmonary bypass identified a urine flow rate of <1.5 mL/kg/h as a cutoff that was associated with AKI risk [30].…”

“…Along with the usual <0.5 or <0.3 mL/kg/h cutoff of oliguria, our analysis suggested significant associations between low urine flow rate of <1.0 mL/kg/h and risk of AKI after LDLT. We evaluated the cutoff of oliguria up to 3.0 mL/kg/h because previous studies reported different cutoffs of oliguria during surgery [30,31,32] (Supplemental Table S2). The significant threshold of <1.0 mL/kg/h may be influenced by the intraoperative diuretics use.…”

Current concepts of fluid management in enhanced recovery pathways

“…5,58 Although traditionally oliguria is taken as a sign of hypovolaemia and subsequent reduction in kidney perfusion, perioperative oliguria now is not always abnormal, especially when no other signs of hypoperfusion are present. 5,59 In a recent study, there was no significant correlation between oliguria and postoperative renal failure, but there was an increase in acute kidney injury associated with increased postoperative fluid balance. 60 Although anuria is abnormal and should be taken seriously, oliguria, however, can be a normal and expected occurrence as a result of judicious fluid management in the perioperative period.…”

Oliguria in critically ill patients: a narrative review

“…No correlation was found for a cut-off between 0.3 and 0.5 mL/kg/h and the development of postoperative AKI [ 16 ]. These findings provide further support for interpreting oliguria within the clinical context in that a relatively reduced urine output albeit greater than 0.3/ml/kg/h is likely to represent a (reversible) physiological response to perioperative stimuli including intravascular hypovolemia, reduced renal perfusion due to hypotension and release of anti-diuretic hormone in response to nausea or pain [ 31 ]. Ralib et al were able to confirm by analyzing 725 admissions to a general ICU, that a urine output threshold of 0.5 ml/kg/h may be too liberal given that a threshold for 6-h UO of 0.3 ml/kg/h was best associated with the combined endpoint of dialysis or mortality.…”