Acute kidney injury (AKI) is a common complication after adult cardiac surgery, affecting approximately 1 in 5 patients and conferring higher mortality, longer hospitalization, and increased resource use.¹ Treatment after established cardiac surgery–associated AKI (CSA-AKI) is supportive; therefore, prevention and early identification of modifiable risk factors remain central.

During cardiopulmonary bypass (CPB), indexed oxygen delivery (DO₂i) is determined by pump flow and arterial oxygen content, which is strongly influenced by hemoglobin concentration. Ranucci and colleagues identified a nadir DO₂i threshold of approximately 272 mL/min/m², below which postoperative renal dysfunction increased, and a subsequent multicenter randomized trial tested goal-directed perfusion targeting DO₂i ≥ 280 mL/min/m².^2,3 “These studies established threshold-based DO₂i targets as an actionable perfusion variable.”

However, a single nadir value may oversimplify a dynamic physiological exposure. Reported DO₂i thresholds vary between studies, and risk may depend on the lowest value reached and the duration and recurrence of low oxygen delivery. Time-dependent and cumulative approaches, including time below the threshold and area-under-the-curve measures, may better capture oxygen delivery deficit during CPB.^4,5 Accordingly, DO₂i is one dynamic exposure among the multifactorial determinants of CSA-AKI, not an isolated prevention target.

This systematic review and meta-analysis evaluated the association between DO₂i and CSA-AKI in adult cardiac surgery. The primary objective was to assess whether threshold-based DO₂i cut-points are transportable across studies. Secondary objectives were to compare threshold models with continuous, time-dependent, and cumulative exposure representations, and to summarize evidence from goal-directed perfusion interventions.