Relationship between difference of preoperative and cardiopulmonary bypass mean arterial pressure, and acute kidney injury in cardiac surgical patients undergoing valve surgery.

Background: Modifiable and non-modifiable factors contribute to development and progression of acute kidney injury (AKI) during cardiac surgery. We hypothesized that, the difference between preoperative mean arterial pressure (MAP) and the average mean arterial pressure maintained on cardiopulmonary bypass (CPB) would be strongly predictive of AKI. We also measured plasma Neutrophil gelatinase-associated lipocalin (NGAL), to establish its association with cardiac surgery associated-AKI (CSA-AKI).

Methods: One hundred and twelve high-risk patients undergoing valve, and valve plus coronary artery bypass grafting (CABG) surgery under cardiopulmonary bypass (CPB) were included in this study. Delta mean arterial pressure (MAP) was calculated as the difference between the average of pre-operative and on-bypass MAP, and blood was sampled for NGAL levels, at baseline, and 6-h after CPB. Detailed data collection was done, tabulating most of the factors which might influence development of post-operative cardiac surgery associated-AKI (CSA-AKI). To define CSA-AKI within the first 24-h post-operatively, the Kidney Disease Improving Global Outcomes (KDIGO) classification was used.

Results: Out of 112 patients, 44 (39.3%) developed CSA-AKI postoperatively. With an ROC analysis cut-off of delta MAP of more than 25.67 mmHg, 46.4% patients developed post-operative AKI, and the average CPB flows which were 1.8 ± 0.2 were not contributory to the development of early CSA-AKI. In our study, ELISA test for human NGAL was performed on serum samples, and the estimated cut-off value of 1661 ng/mL was found to be significantly associated with early CSA-AKI.

Conclusions: Delta MAP and CPB flows are not related to early post-surgical CSA-AKI in cases with prior high-risk elements. However, baseline serum NGAL, as well as its percent change during the early post-surgical period independently predicted the development of CSA-AKI. This implies that, there may be patients with a higher pre-operative preponderance to develop this complication, which could actually be delineated by the use of serum NGAL estimations at baseline.