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Your kidney test comes back normal after surgery, so you must have recovered. Except the damage can be hiding in plain sight. John Erbey is an epidemiologist by training and the founder and CEO of Roivios, where he works at the intersection of science and business. This episode is based on his article “When normal creatinine hides post-operative kidney injury,” published on KevinMD. He explains why kidney function is dynamic, like the heart, and why the reserve you lose during surgery rarely returns even when creatinine looks fine. You will hear what a JAMA Network Open study found about elevated death and complication risk in the years after a “normal” recovery, why readmissions blamed on heart failure or infection may trace back to the kidney, and why John makes the case for protecting the kidney during the riskiest windows, from cardiac surgery to sepsis, instead of trusting the discharge number. Press play to learn why a normal kidney result can mislead you, and how to protect the kidney before the damage is locked in.

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Transcript

Kevin Pho: Hi, and welcome to the show. Subscribe at KevinMD.com/podcast. Today we welcome John Erbey. He’s a health care executive. Today’s KevinMD article is “When normal creatinine hides post-operative kidney injury.” John, welcome to the show.

John Erbey: Thank you. Thanks for having me.

Kevin Pho: All right. So before we talk about your article, just briefly share your story, and then we’ll jump right into it.

John Erbey: Sounds good. So I’m not a clinician. I’m an epidemiologist by training, and I jumped right into industry. I’ve developed a passion for translating science into business.

Kevin Pho: Excellent. And why did you decide to write this particular article on KevinMD?

John Erbey: There seems to be an apparent disconnect, and that’s caught my attention over the last couple of months. At a population level, from the epidemiologic view of it, any decrement in kidney function leads to bad outcomes, whether that’s increased cost or poor events. But at the clinician level, in the patient conversation, that’s rarely discussed. And the implication is that by the time you catch on to those injuries happening, it’s already late in the game, and we needed to have intervened years ago, not today.

So to me, the conversation is about why the kidney doesn’t get blamed or implicated in this health care crisis that we’re in today.

Kevin Pho: Now, why is that? Why does the kidney sometimes get overlooked?

John Erbey: Because it’s not the direct cause. At the end of the day, the kidney is responsible for maintaining the body’s internal environment. When that doesn’t happen, it puts stress on other organs. For example, arrhythmias in the heart are an electrolyte issue, and the kidneys are responsible for maintaining electrolyte levels. Acute heart failure, showing up with congestion and fluid overload, is again the kidney, which is responsible for keeping the volume under control.

All of these events happen, and the kidney is silently chipping away at everything else in the system. So we need to focus there and make sure the kidneys can do their job and keep the body in check.

Kevin Pho: Now, in your article, you specifically talk about post-operative kidney injury and why a normal creatinine hides anything to do with the kidney after surgery. So for those who didn’t get a chance to read your article, give us more detail about what it’s about.

John Erbey: So basically, what we’re talking about is that typical conversation where, after surgery, you get a rise in creatinine, but by the time you go to discharge it’s normal, so you’ve recovered. That’s not really the case. At the end of the day, most people don’t appreciate that kidney function is dynamic, just like the heart. Just as with resting heart rate variability, you have a renal functional reserve, an ability to compensate for a heavy meal or whatever. When that function gets chipped away at, you no longer have the capacity to handle that increased load, and so you end up getting into trouble much faster. It’s sort of a slippery slope. That’s really the premise for the article.

Kevin Pho: Now, you wrote about the JAMA Network Open study, which challenges those assumptions. For those who aren’t familiar with the study, what are some of the findings from it?

John Erbey: So basically, what they found is that even when your kidney function returns to normal, with normal creatinine, you still have a dramatically elevated risk for morbidity and mortality in the coming years. That’s what I talked about in the beginning about the population level. The data is very clear. There’s a nonlinear relationship between the loss of function and the increase in cost over time, and that’s because every time you chip away, every time you move down that spectrum of lost renal function, you accelerate the stress on everything else.

Kevin Pho: So in terms of scenarios like readmissions or repeated hospitalizations that get labeled as heart failure or infection, deteriorating kidney function could be the root cause of both of those scenarios, right?

John Erbey: Certainly a contributor. And at the end of the day, most of these patients have lots of problems, so making sure that you keep the kidney alive and sustain that function for as long as you can will be an important factor in their long-term outcome.

Kevin Pho: So traditional measures like creatinine and estimated GFR are the traditional ways that physicians use to measure kidney function. So how can we tell whether the reserve is compromised? What are some other ways that we can assess kidney function?

John Erbey: So there’s actually a simple test, and it’s a lot like the oral glucose tolerance test that we used to use for diabetes. At the end of the day, if you give a protein challenge to an individual, their GFR should rise, and that rise is predictable. But when you’ve had kidney damage and you’ve lost that function, you no longer see that rise in GFR to help clear the protein load within the body. And it’s not necessarily that the kidneys are clearing the protein load, but it changes all of that volume and fluid dynamic, and that’s really what the kidneys are responsible for.

Kevin Pho: And when should that protein load test be done? What are some of the indications for doing that test?

John Erbey: Well, the test is a research tool at the end of the day.

Kevin Pho: OK.

John Erbey: Where we need to think through it clinically is this: Let’s start with the conversation that baseline creatinine is not necessarily the most informative tool. It’s funny, the kidney is an amazing organ. We measure function based on filtration, but that’s not what makes the kidney unique. What makes the kidney unique is the ability to reabsorb salt, water, and glucose against the forces of diffusion. That’s an incredibly energy-dependent process, and we never talk about that in the concept of kidney function.

Now, the good news is they’re correlated, so as you lose filtration, you lose everything else. But it’s the concept that, first, it’s dynamic, and second, once you’ve lost that reserve, it’s likely not coming back.

Kevin Pho: Now, before any type of procedure, and I think you wrote in your article specifically that cardiac surgery patients are most susceptible, how can we measure kidney function? What should be done instead, if you say creatinine is a relatively crude tool? What else can we do clinically?

John Erbey: Yeah. So we know that patients with renal impairment who undergo these acute stressors, basically any ICU condition. Cardiac surgery is the one that’s been best studied, that and sepsis. So you have this dynamic where you know the patient who’s at risk, and you know the time period that they’re going to be at most risk. It’s while they’re on the pump run and immediately thereafter. And it’s about making sure that we take care of the kidney as part of that concept, so that we don’t damage and lose function.

Because, to be honest, let’s take even a heart attack. Most people don’t view that necessarily as a kidney threat. But ischemia is very profoundly impactful to the kidney, because it operates at a level of near hypoxemia to begin with. And so any stressors that challenge the ability to deliver and consume oxygen are very susceptible to the kidney.

Kevin Pho: So a lot of this is a paradigm shift from managing the complications that can arise from not looking at the kidney carefully enough, to preventing these complications in the first place. Now, in your ideal scenario, can you give us a case study or example of what exactly that would look like? It could be hypothetical. Just tell us a story about what preventing future kidney issues would look like in the preoperative phase. What would be a success story?

John Erbey: So there are two things there. One, by managing, and there are plenty of protocols for this. ERAS is one that I think is the cleanest, where you need to manage the toxins, you need to manage the fluids, you need to manage the exposures, so that you decrease the risk of an injury occurring. And to be honest, we’re investing in the space because we have an investigational product that we hope will be suitable for this case. But at the end of the day, that trial is still ongoing.

Kevin Pho: What are some of the approaches that we have to look forward to when it comes to preventing kidney disease? What are some technologies? What are some general approaches that we have to look forward to when it comes to monitoring and preventing kidney disease, especially in the postoperative setting?

John Erbey: So I’m personally excited about how Medicare is taking a more proactive approach to identifying and managing this problem going forward. We’ve spent a lot of time and energy on the value-based care approach, trying to reduce hospitalizations. That’s proving challenging. And so now they’ve pivoted and moved toward this TEAMS model of identifying high-risk, high-acuity episodes and bundling them together, so that we can figure out what works and really put the stress on the implementation. That way, we will learn very quickly what works and what doesn’t work, and can apply that to broader populations.

Kevin Pho: And specifically with the bundled approach, for those who aren’t familiar with Medicare payments, what exactly would that look like specific to kidney injury?

John Erbey: So it’s a paradigm shift. Essentially, instead of just using that DRG system where you get paid one check for whatever the admission was, they’re now wrapping in a 30-day episode of care. So longer ICU stays, discharge to skilled nursing, and readmissions all get bundled in under that same payment structure. So they’re on the hook for doing what they can to improve recovery and get the patients out into the community.

Kevin Pho: We’re talking to John Erbey. He’s a health care executive. Today’s KevinMD article is “When normal creatinine hides post-operative kidney injury.” John, let’s end with some of your take-home messages that you want to leave with the KevinMD audience.

John Erbey: Make sure they leave with the kidney they came in with. And that’s not just necessarily getting back to normal at the end. It’s making sure that you try to blunt that rise during the times of acute stress.

Kevin Pho: John, thank you so much for sharing your perspective and insight. Thanks again for coming on the show.

John Erbey: Thanks for having me.