Non-linear associations between renal perfusion pressure indexes and AKI incidence and recovery rate.

Background: Renal perfusion pressure plays a crucial role in the pathophysiology of acute kidney injury (AKI). While multiple methods are available for calculating renal perfusion pressure, the optimal calculation approach and its true correlation with AKI remain uncertain. This study aims to investigate the nonlinear relationship between various perfusion pressure indices and AKI, clarifying the connection between perfusion pressure, AKI onset, and recovery.

Methods: Three renal perfusion pressure indices were calculated: MAP-CVP, MAP-Plateau pressure, and MAP-CVP-Plateau pressure. Restricted cubic spline (RCS) analysis was used to examine the association between these perfusion indices and AKI incidence. The relationship between MAP-CVP-Plateau pressure and both AKI occurrence and recovery rate was further assessed through linear spline function and categorical analysis.

Results: A total of 8,848 ICU patients were included in the study, with an overall AKI incidence of 40%. RCS analysis revealed nonlinear relationships between the three perfusion indices and AKI incidence, each demonstrating different thresholds. ROC analysis indicated that MAP-CVP-Plateau pressure (cutoff value of 55) had the highest predictive value and was thus selected as the primary perfusion index. In the linear spline analysis, a high MAP-CVP-Plateau pressure was significantly associated with a reduced AKI risk when MAP-CVP-Plateau pressure was < 55 (OR 0.95, 95% CI 0.94-0.96, p < 0.01), while this association reversed when MAP-CVP-Plateau pressure exceeded 55 (OR 1.02, 95% CI 1.01-1.03, p < 0.01). For AKI recovery, a high MAP-CVP-Plateau pressure was significantly associated with a higher recovery rate when MAP-CVP-Plateau pressure was < 55 (OR 1.02, 95% CI 1.01-1.04, p < 0.01). However, when MAP-CVP-Plateau pressure was > 55, an elevated MAP-CVP-Plateau pressure was associated with a lower AKI recovery rate (OR 0.96, 95% CI 0.94-0.98, p < 0.01). The categorical analysis results for AKI incidence and recovery were consistent with the nonlinear relationship identified in the RCS analysis.

Conclusions: This study underscores the critical role of perfusion pressure, particularly MAP-CVP-Plateau pressure, in AKI pathophysiology. Both low and high MAP-CVP-Plateau pressure levels were associated with increased AKI incidence and decreased recovery rates in critically ill patients.