Near the end of Swapnil’s sweeping summaries of the renal denervation articles for this week’s NephJC, he discussed safety. In the trials, the procedure was remarkably safe but Swap brought up possible future consequences. These are adverse events that could never be measured in a real-world trial:
Renal denervation is permanent. Blood pressure medications can be stopped. Why does this matter? Maybe if a patient subsequently develops sepsis or hypovolemia? The sympathetic system exists for a reason….See this case report. In this study of sheep with CKD, bleeding caused a much more severe drop in blood pressure.
This reminds me of bariatric surgery. We had been doing Roux-en-Y for weight loss for decades (See meta-analysis) when, in 2005, Nelson published a case series of calcium oxalate stones, including a couple of cases of ESKD with dialysis dependence due to oxalate nephropathy. Their work was backed-up in this report.
Oxalate nephropathy is secondary to increased oxalate absorption following the Roux-en-Y procedure. There are two theories as to why this is:
- Fat malabsorption, one of the goals of the therapy leads to saponification of intestinal calcium. Since calcium is unavailable to bind and trap oxalate in the gut more is available for passive and active oxalate absorption in the distal ilium.
- Decreased bile acid reabsorption in the gut leads to unconjugated bile salts damaging the luminal membrane and increased passive oxalate absorption.
Additionally the malabsorption leads to diarrhea and metabolic acidosis. This decreases urine pH and lowers urinary citrate both of which promote calcium oxalate stones. There is also a decrease in urine volume of about 0.5 liters, further increasing the stone tendency of these patients. Dr. Park defined a lot of this in a prospective study of 24-urines after Roux-en-Y.
I have seen patients with ESKD from Roux-en-Y. It is horrible. Since the primary pathology has not ceased, these patients are at risk for the same oxalate nephropathy following a transplant, making a transplant a risky procedure.
Though oxalate nephropathy after Roux-en-Y does occur, obesity itself is a risk factor for ESKD and bariatric weight loss appears to protect patients from this.
This good news tempered with the risk of disaster makes the decision to go for bariatric surgery a bit more nuanced than it is often portrayed. Does renal denervation have similar future land mines just waiting to be exploded in the future? We have no idea what unexpected horrors from renal denervation lie undiscovered.