Abstract Body (Do not enter title and authors here): Background:
Acute kidney injury (AKI) is common following pediatric cardiopulmonary bypass (CPB) surgery and associated with worse outcomes. Maintaining optimal blood pressure has been associated with less AKI in adults but has not been evaluated in children. We examined the relationship between hypotension and AKI in children following CPB.

Methods
This single centre, retrospective study included all children undergoing CPB between 2018-2022, who had continuous blood pressure recorded following critical care admission. Those with pre-existing primary kidney disease, preoperative AKI, and transplant patients were excluded. The association between hypotension (defined as a mean arterial blood pressure <5th percentile for age lasting >5 minutes, recorded in 5 second intervals) and time to > moderate AKI (2/3 AKI; defined by KDIGO creatinine) was analyzed using competing risk methods modelled using cause-specific hazard regression, adjusting for important patient, surgical, and postoperative support variables. Longest duration of hypotension, cumulative hypotension, and burden of hypotension (area under the curve of duration and magnitude of hypotension) were also assessed.

Results
Overall, 1596 patients – 47% (n=818) female – underwent 1763 surgeries at a median age of 0.6 (IQR 0.3-4.6) years. Only 140 patients had >2 surgeries. Hypotensive events occurred after 731 surgeries (42%), all first episodes within 71 hours of CPB (Image 1a). The cumulative incidence of Stage 2/3 AKI occurred in 12% (95% CI 10%,14%) of patient surgeries, 24% within 6 hours of CPB (Image 1b). After adjusting for important covariables, hypotension was associated with an increased stage 2/3 AKI [adjusted HR=1.74 (95% CI 1.16,2.61), p=0.008]. The longest episode (p=0.04, Image 2) and burden of hypotension (p=0.012, Image 3) were also associated with risk of stage 2/3 AKI when modified by age; cumulative time in hypotension was not. A lower threshold of hypotension was not associated with an increase the risk of 2/3 AKI.

Conclusion
Hypotension post CPB surgery is associated with a 74% increased risk for stage 2/3 AKI. Further research is needed to understand the complex interplay of intraoperative and post-operative pathophysiology that leads to kidney injury.