In this study, we confirmed an independent nonlinear relationship between preop-eGFR and postoperative thirty-day mortality. A stable U-shaped trend can be seen in this relationship. When preop-eGFR ≤ 98.688 mL/min/1.73 m2, the thirty-day mortality would be decreased by 1.6% for each additional unit of Preop-eGFR. While preop-eGFR > 98.688 mL/min/1.73 m2,there would be a 1.3% increase of thirty-day mortality rate for each additional unit of preop-eGFR. CHF, DM, IHD and anemia complications (CHF, DM, IHD acting as a promoting factor, while anemia as an inhibitory factor) interfere with the effect of preop-eGFR on postoperative thirty-day mortality.
Studies has already been proved that preop-eGFR is a powerful and independent predictor of thirty-day morbidity risk after surgery [4, 10, 13, 26–27][15][16, 26]. Even in some literature reports, preop-eGFR is the strongest predictors of posttransplant survival [26]. Preop-eGFRs is a important indicator of many adverse surgical outcomes[16], as acute kidney injury, significantly related to higher mortality. At the same time, DM, IHD, CVF, and blood transfusion also are risk factors for poor postoperative prognosis [6]. The current research population is mainly concentrated in transplant [26], cardiac [10, 13] and neuro[14] surgery. There is still a lack of research on other surgery. There are two articles that define the study population as non-cardiac surgery patients. Jacek B. Cywinski, at al evaluated 92,888 patients undergoing non-cardiac surgery, and confirmed preop-eGFR is a scientifically feasible predictor of postoperative thirty-day mortality [4].J. R. Prowle et al. reported that significantly increases the risk of death after non-cardiac surgery, according to the data of 36 779 cases[2].
Previous studies mostly focused on the patients of renal insufficiency to verify the important regulatory role of preop-eGFR[12–13, 15]. High preop-eGFR levels have also been connected with greater mortality among nonsurgical patients indicating a potential U-shaped association of preop-eGFR with poor prognosis [28–30]. A recent study revealed the association of the specific trend between preop-eGFR and thirty-day mortality in patients undergoing surgery for gastrointestinal malignancies, without clarifying the inflection point[16]. In addition, the current research population is mainly Europeans and Americans, and rarely Asians.
To our best knowledge, it is the first time that the specific U-shaped relationship between preop-eGFR and postoperative thirty-day mortality has been clearly identified in Asian patients undergoing non-cardiac and non-neuro surgery, ranging from minor day cases to major surgeries.
Strengths of our study are mentioned as follows: firstly, the generalized additive model was used to evaluate non-linear relations, instead of using the generalized linear model to illustrate the linear relationship only. Secondly, as an observational study, there were some unavoidable potential confounders included in this study. In order to minimize residual confounding, strict statistical adjustment was performed. What’s more, effect modifier factor analysis makes the use of data better. Sensitivity analysis was performed of these data to ensure reliability.
The findings of this study should be helpful for reducing the risk of postoperative death. The preop-eGFR at which the rate of the perioperative Mortality was lowest was 98.688. It suggests that regulation of preop-eGFR can effectively reduce perioperative mortality, especially with CHF, DM, IHD comorbidities. While comorbid with anemia, it becomes the same important to control anemia for reducing mortality.
This study has several acknowledged limitations. First, as for our study is a secondary analysis based on the published data, we cannot exclude some residual and/or unmeasured confounders (such as socioeconomic factors and inflammatory markers), that may bias the estimated relationship. Secondly, the study population, which only included Asian patients, can be further expanded to conduct multi-center research to increase the reliability of the data. Our choice of outcomes and variables is also limited. We could not investigate the relationship between preop-eGFR with long-term outcomes. What’s more, when it comes to high preop-eGFR, the results would be much more accurate formula based on cystatin C, instead of basing on creatinine. However, cystatin C haven’t be widely used in clinical practice right now[31].