Discussion:
Our results suggest that eGFR, ≥3 coronary anastomoses, preoperative IABP implantation and prolonged ventilation time are independent risk factors for AKI in elderly patients undergoing CABG.
The incidence of AKI was 27.5% in our study which is similar to the value reported in previous studies. The incidence of AKI in elderly patients was lower than that in Wilko Reents’
study19. On the one hand, the reason may be that 40% of the patients had renal insufficiency before the operation in the Wilko Reents’ Study. On the other hand, cardiopulmonary bypass surgery is closely related to acute kidney injury 14, and only 17.1% (74/432) of the patients in this study received coronary artery bypass grafting under cardiopulmonary bypass, while more than half of the patients in the Wilko Reents’
study received cardiopulmonary bypass surgery.
Previous studies have shown that preoperative anaemia and proteinuria were also independent risk factors for AKI after surgery20,21. According to the latest literature, these indicators were included in our study, but the final results were not consistent with those of previous studies. On the one hand, the results from previous studies may not be representative of elderly patients; on the other hand, the sample size of our study was insufficient.
eGFR was a risk factor for AKI in this study, which is consistent with many previous studies. Preoperative IABP implantation is an independent risk factor, which indicates that the use of IABP in elderly patients has greater impact on renal function. This is consistent with previous studies22-24. It is suggested that early operation after IABP implantation may reduce the incidence of AKI. In addition, the revascularization of more than 3 coronary anastomoses is a protective factor for AKI, which suggests that complete revascularization can not only benefit the heart but also benefit the renal function. A prolonged ventilator time can increase the incidence of AKI, which suggests that the occurrence of AKI can be reduced in patients if they can recover spontaneous breathing as soon as possible. This suggests that preoperative pulmonary function exercise is quite important.
In terms of postoperative complications, the mortality, postoperative myocardial infarction and reoperation rates in the AKI group were higher than those in the non-AKI group. Previous studies showed that acute kidney injury after coronary artery bypass grafting was associated with a long-term risk of myocardial infarction. Three percent to seven percent of patients undergoing CABG experienced myocardial infarction within one year after surgery 25. Therefore, our study also suggests that AKI may be closely related to the occurrence of myocardial infarction and may even lead to postoperative death.
The limitations of this study were as follows: on the one hand, this study was a single-center, retrospective study, with certain selection bias; on the other hand, the sample size calculation suggested that the size was small and a larger sample needs to be included in future analyses. Finally, in this study, the diagnosis of AKI was based on KDIGO criteria. Because diuretics are used in many patients after surgery, urine volume was not used as one of the diagnostic criteria of AKI.