What is the significance of intra-operative oliguria with regard to post-operative acute kidney injury? A physiology-informed framework for intra-operative oliguria management

BACKGROUND: Intra-operative oliguria is frequently interpreted as a surrogate for hypovolaemia or impaired renal perfusion, often prompting reflexive and potentially harmful fluid administration. However, urine output during anaesthesia is influenced by a complex interplay of neurohormonal activation, surgical stress, and positive pressure ventilation, which can decouple diuresis from actual renal blood flow. This perspective articles critically appraises the evidence linking intra-operative oliguria to acute kidney injury (AKI) and explores the physiological pitfalls of interpreting urine output as an isolated haemodynamic target. RESULTS: Recent high-level evidence confirms a significant correlation between intra-operative oliguria and post-operative AKI, yet also highlights substantial heterogeneity in the thresholds and durations used across clinical practice. To address this, we propose a conceptual, physiology-informed framework that categorises reduced urine output into four distinct clinical phenotypes: adaptive (a physiologic neurohormonal response to stress), haemodynamic (potentially reversible hypoperfusion), high-risk/complex (occurring in major surgery or vulnerable patients), and injury-associated (established renal damage). In one highly selected high-risk population, a single randomised trial reported that targeting supranormal, urine-guided hydration was associated with a lower incidence of AKI. These findings are hypothesis-generating only and should not be generalised, but they raise the possibility that oliguria in narrowly defined contexts may represent a potentially modifiable signal warranting further prospective study rather than passive observation. Bedside adjuncts, such as ultrasound assessment of cardiac output or venous congestion, may assist in differentiating these phenotypes, although their intra-operative validation remains limited. This framework is intended as a hypothesis-generating conceptual aid to clinical reasoning, not as a validated clinical algorithm or practice recommendation. CONCLUSION: Interpreting intra-operative oliguria requires a fundamental shift from binary thresholds to context-dependent phenotyping. Effective management must prioritise individualised assessment-integrating surgical risk, baseline patient vulnerability, and dynamic monitoring-rather than responding to isolated urine output triggers.