Nomogram is a visualization of regression analysis, which is widely used in clinical disease diagnosis and prognosis evaluation [9–12]. In this study, we developed and validated a novel nomogram to predict the mortality risk among elderly patients with ARF. Our results show that this nomogram mainly based on vital signs and laboratory examination. The initial vital signs include heart rate, respiratory rate, systolic blood pressure and SpO2 were identified as an independent predictor of mortality in elderly patients with ARF. With the increase of heart rate and respiratory rate, the risk of death increases. Furthermore, the decrease of systolic blood pressure and blood oxygen saturation will also increase the risk of death, both of which have a greater weight in the evaluation of short-term prognosis. It can be seen that both maintaining circulation stability and increasing blood oxygen were helpful to reduce the mortality of ARF in the elderly.
Currently, urinary output and serum creatinine are used to evaluate kidney function.
However, a study has shown that serum creatinine was an unreliable indicator of acute changes in renal function[13]. Our study also showed that urinary output was superior to serum creatinine in predicting short-term mortality of elderly patients with ARF. Although, the assessment of AKI stage is not necessarily based on urine volume, the initial postoperative urine volume was considered an accurate predictor of delayed graft function[14]. The reduction of urinary output can be attributed to insufficient blood flow to the kidneys, due to reduced blood volume and systolic pressure. Albumin, synthesized by the liver, are considered important factors associated with malnutrition among patients. It tends to improve the microcirculatory performance which supports the maintenance of major organ functions[15]. Thus, albumin was regarded as an important biomarker to evaluate the poor prognosis of hospitalized patients[16]. Our research also showed that the risk of death increased gradually with the decrease of plasma albumin. Therefore, plasma albumin may play an important role in predicting the mortality of elderly patients with ARF.
Finally, the nomogram incorporates 6 items of heart rate, respiratory rate, systolic blood pressure, SpO2, urinary output and plasma albumin. In order to prove the calibration of the nomogram, clinical data was collected from different institutions. As is well known, the internal validity associated with the explanation of the results, and the external validity related to the generalizability of the results [17, 18]. Through the internal and external validation data set analysis, the calibration of our nomogram has been proved to be highly consistent, which was more accurate than APS-III (B) and SOFA scores. At present, SOFA score has been widely used in assessment of critical diseases[19, 20], especially in the prognosis of multiple organ failure. Compare our nomogram with these scores, it has fewer indicators, but better discrimination and calibration. This means that our nomogram may be popularized to predict the outcome of elderly patients with ARF.
However, to evaluate its clinical usefulness, it depends on how much it benefits the patient, not just its popularization[21]. DCA is a novel method which has been widely used in the evaluation of clinical research effectiveness[22–24]. It offers insight into clinical consequences on the basis of threshold probability, from which the net benefit could be derived[25]. According to the DCA results, the application value of our nomogram is better than that of APS-III (B) and SOFA scores.
Our study has several limitations. First, this study was a single center study, and the validation set was from the same hospital. We need validate our nomogram in broad external population. Second, our nomogram is only applicable to the elderly ARF patients. Third, we reported 30-day all-cause mortality instead of ARF specific decease cause.