AKI develops in 7.5% of patients undergoing noncardiac surgery [10] and the postoperative development of AKI is associated with an eight-fold increased probability of death within 30 days of surgery [11]. Interestingly, the previously reported incidence of AKI in patients undergoing cardiac surgery varies between 4 and 9% [12, 13], compared to between 15.3 and 16% for hip fracture surgery [2, 7]. Despite the significant association between AKI and hip fractures, the importance of AKI in patients with femoral neck fracture has only recently received attention. In the present study, the incidence of AKI in patients who underwent femoral neck fracture surgery was 17.7%, which was consistent with previous reports [2, 7]. There was a significant difference in the prevalence of diabetes, pre-existing renal disease, preoperative Hb level, preoperative BUN level, preoperative Cr level, type of operation, and intraoperative hypotension between the AKI and non-AKI groups. After controlling for confounding variables, intraoperative hypotension was the only independent risk factor for AKI.
Bipolar hemiarthroplasty, rather than THR, was significantly associated with an increased risk of AKI in this study, although THR leads to massive blood loss and prolonged operating time because of its invasive and meticulous surgical technique. One possible explanation is that the patients who underwent bipolar hemiarthroplasty were typically older and less ambulatory, owing to the presence of underlying disease. Several studies have demonstrated that the incidence of AKI increases with age and is most common in elderly patients [14, 15]. Additionally, diabetes and pre-existing renal disease have emerged as independent predictors of AKI [16]. Our study also showed independent risk factors, such as laboratory findings (BUN, postoperative serum creatinine, ESR) and diabetes, associated with AKI after femoral neck fracture surgery. Therefore, surgeons should be aware of the possibility of AKI when treating femoral neck fracture in patients with high morbidity.
The use of hypotensive anesthesia is generally recommended in the orthopedic department for decreasing intraoperative blood loss, transfusion requirements, and operation time, improving the quality of the surgical field, and preventing deep vein thrombosis. However, it may lead to intraoperative dehydration and hypotension and dehydration may in turn cause endothelial injury and the subsequent local release of endothelin, angiotensin II, and catecholamines, all of which cause vasoconstriction and exacerbate ischemia in the kidney [17, 18]. A clear relationship between hypotension during operation and the development of AKI was observed in this study. Therefore, clinicians should consider intraoperative hypotension among the various risk factors for AKI and prioritize intraoperative blood pressure control.
The major limitation of this study was that it did not investigate the total duration of intraoperative hypotension. Although the duration of hypotension required to incur damage is unclear, interest in the effects of the duration of intraoperative hypotension on AKI has recently increased [9, 19]. In addition, there are almost 50 different definitions of intraoperative hypotension in the recent literature [20], which may reduce the generalizability of our findings, although we used the most common definition [9]. Thus, future investigations that establish a clear definition of intraoperative hypotension and determine the critical duration of intraoperative hypotension are warranted.
