Abstract
<jats:p>Background/Objectives: Mean arterial pressure (MAP) is an incomplete surrogate of systemic perfusion: cardiac index (CI) and MAP can become dissociated. Recent cardiac surgery studies report that the burden of low CI during normotensive periods is associated with acute kidney injury (AKI). Whether this pressure–flow dissociation occurs in major aortic surgery and is modulated by the choice of arterial-pressure-derived monitoring strategy (FloTrac vs Acumen IQ/Hypotension Prediction Index, HPI) is unknown. Methods: CI-focused secondary analysis of 100 major aortic surgery patients from a prior MAP-based cohort. Continuous CI signals were newly extracted from the original HemoSphere exports. The primary metric was the percentage of monitoring time with CI &amp;lt; 2.2 L/min/m2 during MAP ≥ 65 mmHg; the primary outcome was AKI by KDIGO criteria. Multivariable logistic regression adjusted for baseline demographics, comorbidities, preoperative MAP, surgery duration, and monitoring strategy, with Holm–Bonferroni correction within test families. Reported per STROBE. Results: Pressure–flow dissociation was frequent: low CI during normotension occurred in 94% of patients at CI &amp;lt; 2.5 (median burden 27%). The HPI group had numerically lower low-CI burden and higher mean MAP (87 vs 84 mmHg, praw=0.008). AKI occurred in 34/99 evaluable patients (FloTrac 19/49, 38.8%; HPI 15/50, 30.0%). AKI patients did not have higher low CI burden than no-AKI patients (median 5.2% vs 7.6%, p=0.73). In multivariable regression, neither low CI burden (adjusted OR 0.88 per 10-pp increase, 95% CI 0.67–1.12, p=0.33) nor HPI assignment (adjusted OR 0.57, 95% CI 0.20–1.53, p=0.27) was associated with AKI. Sensitivity, time-to-event, and heart rate × CI interaction analyses yielded uniformly null findings. Conclusions: Pressure–flow dissociation is frequent in major aortic surgery, and HPI monitoring modifies the haemodynamic pattern. However, neither the low CI burden nor the choice of monitoring strategy was associated with postoperative AKI, suggesting a boundary condition on the generalisability of recent cardiac surgery CI–AKI associations. Definitive evidence requires prospective randomised evaluation (HYPE-AORTA, NCT07510451).</jats:p>