The results of the present study suggested that the ML model could be an effective tool for risk stratification and prediction of post-transplant AKI stage 3 for individual patients. The performance of the ML model was superior to that of the existing clinical metrics alone (eGFR or SCr). To the best of our knowledge, this study is the first to evaluate the predictive capability of ML methods for the assessment of severe postoperative AKI in patients undergoing HT.
Early identification and prevention of AKI in patients undergoing HT may play an important role in selecting treatment regimens and thus improving prognosis, given the high short- and long-term mortality risks associated with AKI after HT. If acute renal failure happens, the short-term mortality increases 3.5-fold and 1-year mortality 2.3-fold1. However, the ability to accurately identify high-risk patients who may develop AKI is a major challenge in clinical practice. Although traditional risk factors for the prediction of post-transplant AKI have been identified, they are population-based tools 7,12, which are less effective for individual risk evaluations. Furthermore, the traditional features to predict post-transplant AKI from existing models have relatively limited predictive performance17, highlighting the need for a more precise model for personalized treatment decisions.
Analyzing and integrating the numerous risk features in an individual patient can be a confounding task for the clinician. The increasing number of clinical features influencing risk stratification from various medical checks amplifies the intricacy of assessment and makes it more difficult for clinicians to make a correct decision involving risk stratification in an individual patient. Moreover, the unanticipated aspects of possible interactions between a few weaker risk features in an individual patient are frequently underestimated11. Machine learning, both supervised and unsupervised, can overcome these challenges by deep integration of the experimental and clinical datasets to build powerful risk models and reclassify patient groups18.
Our results demonstrated that by the integration of clinical information, experimental datasets, and ultrasonography-derived metrics, the ML model (AUC:0.828) showed superior risk prediction for AKI stage 3 compared with preoperative eGFR (AUC: 0.694) and SCr (AUC: 0.525) alone. These features had been identified as predictors of AKI by logistic regression analysis in previous studies 12,19,20. However, the numbers of features included in the analyses of these studies were limited to decrease the interactions between features. In our study, the ML model provided an excellent value in prognostic performance while considering 51 features and potential feature–feature interactions in patients. This characteristic permits a deep exploration of all available data for non-linear patterns that could predict the risk stratification of a particular individual15.
As reported in previous studies, the occurrence of AKI is a consequence of multiple multifactorial interactive methods that cannot be interpreted in the context of a single etiologic factor17,21,22. In the light of our findings, CysC, eGFR, RA-l, and SCr were all predictive factors included in the ML model for predicting the development of AKI stage 3. In particular, CysC, a biomarker for the quantification of kidney function loss, was the most related predictive factor in patients with AKI stage 3, and it may have the ability to detect AKI one to two days before the rise of SCr with higher accuracy and precision 23. Furthermore, except for acute renal failure, no other factors were found to alter CysC levels, enhancing its effectiveness as an endogenous marker for predicting AKI. Our findings confirm the predictive value of eGFR ranked after CysC, one explanation of this may be that CysC reflects GFR changes more sensitively compared to SCr, and eGFR, used widely in clinical practice instead of GFR, is calculated with SCr in this study23.
Cardiac features can reflect the confluence of heart–kidney interactions through hemodynamic dimensions. The difference between arterial perfusion pressure and venous outflow pressures must be adequately large to keep sufficient renal blood flow and glomerular filtration. In the setting of this concept, the inability of impaired left ventricular function makes low forward flow with reduced left ventricular ejection fraction (LVEF), and consequently leading to prerenal hypoperfusion. Interestingly, we found that LVEF had no significant effect on the development of AKI stage 3. This is supported by previous studies as Jin et al.24 demonstrated that LVEF was not independently and significantly associated with the development of AKI after cardiac operations. This was illustrated by a relative preservation of eGFR derived from efferent arteriolar constriction following on from the renin-angiotensin system to accommodate the reduced LVEF. In patients with markedly reduced renal blood flow exceeding renal autoregulatory capacity, the compensatory increase in eGFR is lost and could evolve into AKI. Alternatively, the elevated central venous pressures, as a result of changes in right heart structure such as an augmented diameter of RA-l, can bring about an increased renal resistance; the kidneys may subsequently become more susceptible to the occurrence of AKI. This mechanism has been presented in clinical researches in patients with cardiac dysfunction using invasive hemodynamic measurements25,26.
Study Limitations
This study has several limitations. First, our research was a single-center study with a relatively limited sample of patients, which may be subject to selection bias; thus, a multicenter study will be needed to confirm our findings. Second, although we appraised 51 diverse features with the ML algorithm, we did not consider additional features, such as cardiac magnetic resonance due to its retrospective nature, that may contribute to better risk prediction. Third, we did not conduct external validation to verify the robustness of our results using an independent dataset from other centers; this is our future research direction.