In our study population, the incidence of postoperative AKI was 12%, slightly lower than the 11.8%-28.4% reported by previous studies for hip fracture patients. These differences can be attributed to various factors, such as varied definitions of AKI, varied monitoring periods, and heterogeneity of the selected patients. However, we do agree that elderly patients with hip fractures or femoral neck fractures are at a greater risk of post-surgical AKI.
Shin et al.(9) and Kang et al.(7) reported that early postoperative hypoalbuminemia is an independent risk factor for AKI, a finding that is in tandem with our results. In this study, early postoperative albumin levels in the AKI group were significantly low than in the no-AKI group (27.54 vs 32.21, p < 0.001). Through ROC curve analysis (AUC: 0.859), the cutoff value of the postoperative albumin level was 29.6 g/L with a sensitivity of 83.8% and a specificity of 78.2%. Moreover, logistic regression analysis indicated that AKI incidences in patients with early postoperative albumin lower than 29.6 g/L were 17.94 times higher than those in patients with more than 29.6 g/L postoperative albumin levels. Therefore, when albumin levels are less than 29.6 g/L in the early postoperative period, albumin should be supplemented in time to protect against postoperative AKI.
Jang et al.(8) reported that intraoperative hypotension is a risk factor for AKI, in accordance with our study. Logistic regression analysis revealed that intraoperative hypotension enhanced the risk of AKI by a factor of 10. In a study involving 138,021 patients, Mathis et al.(16) found that the postoperative AKI in adult patients undergoing non-cardiac surgery exhibited varying associations with distinct hypotension levels. Therefore, it is necessary to monitor and control blood pressure during surgery.
We identified perioperative average hemoglobin to be an independent risk factor for postoperative AKI. Kang et al.(7) reported that postoperative AKI was correlated with blood loss after surgery, and to a certain extent, our results are consistent. Therefore, we recommend blood transfusion for patients who meet transfusion indications. Some studies(17–19) have reported that blood transfusion is also a risk factor for postoperative AKI in hip fracture patients. However, prospective large sample studies are needed to confirm these findings.
Many other risk factors for AKI after hip surgery, such as age, preoperative albumin levels, BMI, preoperative complications, and postoperative complications have been reported(18, 20, 21). In this study, these indicators were not found to be significantly different between the AKI and no-AKI groups. These outcomes could be attributed to differences in populations for different studies. We cannot deny that these factors are high risk factors for postoperative AKI in patients with femoral neck fractures. Therefore, they should be taken into account in clinical work to prevent AKI. More prospective large sample studies are needed to confirm these possible risk factors.
The proposed prediction formula was confirmed by the ROC curve. Its predictive ability was superior to that of perioperative average hemoglobin levels, early postoperative hypoalbuminemia and intraoperative hypotension alone. Using this formula, we intend to demonstrate that multiple factors should be integrated and analyzed to evaluate patients' risk for postoperative AKI.
The limitations of this study are as follows. First, it is a retrospective study, therefore, it is necessary to perform a large-scale prospective study to confirm our findings. Second, since this is a retrospective study, long-term follow-up of patients was not possible to observe changes in long-term creatinine levels and patient survival. Third, due to the limited sample size, staging and related studies of postoperative AKI were not performed. Fourth, the sCr can be influenced by volume overload, nutrition, steroids, and muscle trauma(22). The immediate postoperative period sCr concentrations can be lower than baseline as a result of hemodilution after massive fluid administration and fluid shifts. Biomarkers for the early detection of AKI (23, 24) should be evaluated in future studies.