The impact of preoperative comorbidity and intraoperative hypotension on postoperative acute kidney injury after non-cardiac surgery: a structural equation modeling-based mediation analysis.

BACKGROUND

Preoperative comorbidities are associated with postoperative acute kidney injury (AKI). However, whether this association is direct or mediated by intraoperative hypotension (IOH) is unclear. We hypothesized that IOH mediates the relationship between preoperative comorbidities and postoperative AKI.

METHODS

Data from adult patients undergoing non-cardiac surgery under general anesthesia were analyzed. Inverse probability of treatment weighting (IPTW) was applied to achieve a balance between the exposure groups by reducing the baseline differences in the measured covariates. Structural equation modeling (SEM)-based mediation analysis was conducted using the American Society of Anesthesiologists physical status (ASA-PS) classification ≥ 3 as an input and postoperative AKI as an outcome. IOH (duration of mean arterial pressure < 60 mmHg), along with albumin and hemoglobin levels, was considered a mediator. We also performed interaction analysis between patient sex and age.

RESULTS

After IPTW, 8643.9 (10.8%) patients had an ASA-PS of ≥ 3. AKI occurred more frequently (4.5% vs. 6.9%, P < 0.001) in patients with ASA-PS ≥ 3. ASA-PS ≥ 3 was associated with a total effect estimate of 0.02 on the log-odds of postoperative AKI (P < 0.001). Of the total effect of ASA-PS ≥ 3 on postoperative AKI, 48% was significantly mediated by IOH (26%) and hypoalbuminemia (26%), though anemia showed no significance. The effect of high ASA-PS scores on postoperative AKI was significantly modified by sex, but not by age.

CONCLUSIONS

High ASA-PS scores increase AKI risk after non-cardiac surgery, a relationship partially mediated by statistically significant pathways involving IOH and hypoalbuminemia.