Intraoperative oliguria modifies the association between cardiac power index and postoperative acute kidney injury: a retrospective cohort study.

Abstract

Purpose: Postoperative acute kidney injury (AKI) is common and associated with adverse outcomes. Intraoperative hypotension and oliguria are risk factors, yet management remains mean arterial pressure (MAP)‑centric. Cardiac power index (CPI) may capture pressure-flow conditions, and its association with AKI may depend on intraoperative urine output.

Methods: We analyzed 814 adults undergoing non‑cardiac surgery with FloTrac™ monitoring. AKI was defined by the KDIGO creatinine criteria. The main predictors were CPI0.4_AUT, the time-integrated deficit of CPI below 0.40 W/m², and intraoperative urine output (mL/kg/h). Multivariable logistic regression models, adjusted for the AKI risk index and other covariates, were fitted with and without a CPI0.4_AUT × urine‑output interaction, and average marginal effects were calculated.

Results: AKI occurred in 59 patients (7.2%). Without the interaction term, CPI0.4_AUT was not statistically significant at the 0.05 level (adjusted odds ratio [aOR] 1.02, 95% confidence interval [CI] 1.00-1.04, P = 0.10). With the interaction, CPI0.4_AUT was significantly associated with AKI (aOR 1.05, 95% CI 1.02-1.08, P = 0.004), and the CPI0.4_AUT × urine‑output term also reached significance (aOR 0.97, 95% CI 0.93-0.99, P = 0.03). Average marginal effects showed that higher CPI0.4_AUT was associated with a higher predicted AKI probability at low urine output (< 0.8 mL/kg/h), but this association was minimal when urine output was ≥ 0.9 mL/kg/h.

Conclusions: Low intraoperative CPI with oliguria was associated with a higher predicted probability of AKI, whereas the CPI‑AKI association weakened with increased urine output. Integrating CPI and urine output may help characterize hemodynamic management beyond MAP‑centric management.