*3.3. Bariatric Surgery*

Bariatric surgery, also so-called metabolic surgery, refers to methods used to reduce obesity and improve metabolic abnormalities. The most used techniques are the vertical sleeve gastrectomy, Roux-en-Y gastric bypass, adjustable gastric banding, and biliopancreatic diversion/duodenal switch. Selection of the most appropriate procedure needs to consider not only the morbidity/mortality risk during the procedures but also the potential side effects during follow-up [82]. The surgical treatment of obesity improved management of diabetic and non-diabetic CKD and reduced the rate of renal decline toward ESKD. Once ESKD is established, absolute event rates are low and although complications can be present, it remains a safe intervention. Implementing one of the above surgeries pretransplant increases the potential access to transplantation and, in addition, improves the management of metabolic complications post-transplantation, including new-onset diabetes. Likewise, this may be beneficial as a treatment for potential obese donors [82].

A beneficial impact on obese patients with type 2 diabetes in kidney protection has been emphasized. A large metanalysis concluded that post-surgical reduction in albuminuria is independent of the changes in BMI, HbA1c, and systolic BP [106]. In nondiabetic subjects, randomized studies are not available, but many observational studies have demonstrated the beneficial impact in reducing incidence of albuminuria and the risk for ESKD after an 18 year follow-up [107]. In CKD patients, at the end of the first year post-surgery [108] and after 7 years of follow-up, improvement in the categories of CKD were observed in around half of the patients, and even in patients with very high risk at baseline a quarter of them improved [109].

In patients with ESKD in dialysis, before kidney transplantation, bariatric surgery had a reduction in mortality, incidence of diabetes, and around 60% of cardiac diseases. The preferred method in dialysis patients is the laparoscopic sleeve gastrectomy in which results are more effective with less complications and with the additional advantage of not interfering with pharmacokinetics of immunosuppression drugs [110].

Increment in the incidence of kidney stones has been reported associated with bariatric surgery. Among the factors that contribute to this association are the decrease in urinary volume and citrate, the increased urinary oxalate, and the calcium oxalate saturation. Procedure selection may be critical to mitigate the risks of oxalate nephropathy since more restrictive procedures reduce the risk [111].
