AKI Consult Burke and Tucker

Hey guys, I'm Emma Burke. I'm one of the surgery education fellows with behind the knife. And today I'm joined by Dr. Brian Tucker, an associate professor of nephrology at Baylor college of medicine. And we are going to discuss acute kidney injury as part of our med surg consult series. So welcome Dr.

Tucker. Hi, thank you for having me. Great to have you. So we're going to kind of set the scene with a scenario. We're gonna put ourselves in the mindset of a surgical intern. So you have been taking care of a 55 year old female on the surgery floor. She has a history of diabetes and hypertension, and she's post op day 2 from a right hemicolectomy for colonic adenocarcinoma.

You notice today on her labs that her creatinine has jumped up from 1 at baseline to 2. Unfortunately, when you go to check her Is and Os, you see that her Foley was pulled yesterday, so you don't really know exactly how much urine she's been making. She tells you she's been voiding, but it seems Seems like it's a little bit less than her baseline.

So Dr. Tucker, does this kind of seem like an AKI to you or where should we start? Yeah, it definitely seems like an, an AKI. The KDGO definitions of AKI, you can use three things to diagnose it. It's either a creatinine increase of 0.

3 milligrams per deciliter, uh, in two days. And so it seems like this would fit within that criteria or a creatinine increase of 1.

5 times the basal level within seven days. Or the least I would say used is the urine output of less than 0. 5 mL per kg an hour for 6 hours. But generally any increased short term cramming within a couple days to a week is considered AKI. And so in this case, definitely considered acute kidney injury.

If I'm worried about an AKI on a patient like this, is it worthwhile to put that Foley back in? Or is it okay to just kind of go based on labs? Generally, if the kidney function is getting worse without a clear etiology, having a folein is definitely a good idea. Especially if they're getting closer to needing dialysis.

Like if we're seeing electrolyte problems, acid base problems, fluid overload problems, and we're about to dialyze them, like you're gonna put in a catheter and we're gonna do dialysis, dialysis, dialysis. It would be pretty nice to at least know what their urine output is with a Foley prior to dialysis.

Like, I've had patients where if I put a line in and I notice that I'm a Foley, you put a Foley in and they pee out like three liters and you're like, wow. I would say if it's getting worse, definitely a Foley is a good idea. If it's stable, slowly increasing, you know, we can kind of hold off, but it's really patient to patient.

And I, you know, I'm on the page where if we don't need a Foley, we don't have to pull one. But in most cases, if the creatinine is getting worse, it's definitely a good idea. So in your mind, when you're thinking about AKI, kind of what are your first steps after you get that initial creatinine, that initial BUN, where do you go next?

One of my old attendings told me the most important test or blood test. is the one right before. When you get a number like a crowning of two, you always want to look at where it has been. The progression is super important. So we need progression. And immediately, whenever I get a consult for acute kidney injury, you have to look, uh, how close are they at needing dialysis.

So you have to put in the AEIOUs. And so you have to look at the acidosis. Electrolyte problems, i. e. ingestion, A, E, I, O, overload, and u is uremia. And so if they're close to dialysis or you see the potassium slowly increasing, signs of acid base issues, um, then that's a lot more concerning and that would require a closer follow up and getting us involved sooner.

You know, I kind of remember from med school, they do the whole pre renal, intrinsic, post renal idea for AKI. Is that something that it's helpful if we start working that up before we get medicine or nephrology involved? We always appreciate when the primary teams, whether it's surgery or medicine, start working it up.

It helps because it gives us data when we come on board that we wouldn't have if you hadn't started working it up. It also tells us what you were thinking a little bit, right? If you're ordering all these tests for volume analysis, then my thought is, okay, the team thinks maybe there's a volume problem going

on.

So it gives us a lot of information. But in general, the pre Reno, intrinsic, and post Reno, Is a great way to start for surgery patients, the majority, I would say AK eyes are going to be pre renal and intrinsic. But remember, the key thing is with pre renal, that could mean volume loss. or hyperbolemia because the kidney's in a state of a reduced oxygen consumption because of the reduced flow state if they have heart failure and so pre renal is too little volume or too much intrinsic would be like your common ATN which we see quite quite frequently after like a hypotensive episode and then of course post renal is something like obstruction any patient with reduction of urine output I would say any cancer regardless of where it is.

They're always at risk for post renal. Another thing that, say, a lot of people, medicine or surgeons, don't really notice is, especially after surgery, you're getting a lot of opiates. These often can cause neurogenic

bladder. It's helpful to have those pre renal, intrinsic, post renal categories, but essentially they would all kind of involve the same kind of workup, including like volume, status assessment, apparent light, um, renal ultrasound, etc.

I really liked what you said about the volume overload piece because that's something that I often forget when I'm thinking about like a pre renal. So is an echocardiogram enough for us to go off on that or is there some other kind of test that you guys like to see? It depends, um, on how much evidence I have.

So if they have a history of heart failure and they're coming after holding diuretics. and getting a couple liters positive in, in the OR, I really don't need that much more evidence to say, Okay, this is probably going to be hypervolumine me. Um, or if the patient has like C dip and, and they're not eating and they have 10 liters of diarrhea, you know, like I don't need that much more evidence to say, Okay, we're going to give some fluids.

Of course, I would say the more evidence, the better. And actually KDGO guidelines for like post op AKI

evaluation is to evaluate with echo or some sort of hemodynamic device to evaluate the fluid balance because the most common cause of AKI or at least in my view is going to be volume related problems.

I think from the surgery perspective it's really easy to get caught up in thinking that patients volume down, you know, their belly's been open for hours, they lost some blood in the OR. They're definitely, they need some boluses. You kind of end up giving a couple boluses, the urine doesn't really pick up, and then you think about giving that Lasix.

You give the Lasix and the patient responds, but you're not really sure what helped. Your first thought is not wrong, right? Like urine output goes down. You, you consider it maybe some hypovolemia going on, but it's important. A couple of things to remember that, that And maybe I'm biased. When I get consulted, we're already at this time where it's like, it's too late, right?

But in the beginning processes, when urine output goes down, it could be a lot of things, right? Hypovolemia is part. It could be, like you said, hypervolemia.

It could just be a relatively normal scenario. Sometimes intermittently, the urine output drops. They're, they're going through a stressful situation.

There aren't all these medications, high ADH because of the whatever surgery they're going through. And so it could be a physiological normal response. It's super important that when you see that little urine output, I personally would not do a lot or overreact until I start seeing lab changes. Because essentially, think of it like this.

If the urine output decreases a little bit, but the labs throughout the day to day are, are super stable, the kidney is doing what it needs to do to maintain those labs. When the urine output decreases, maybe you can give some fluids if you think that they're a little dry, but remember, always have the ability to change your mind.

And I, and we see it too often where it's like that diagnostic bias, but it's like, okay, low urine output means hyperbulimia. I'm going to give fluids. Oh, it's not getting better. Give more fluids. Oh, give more, more,

more. Like, I'm just not giving you enough. Yeah, and then you end up, you've given them like two liters, and then you're like, well, I'll do the poor man's dialysis, and now I'll give a little bit of Lasix, and you're not sure what fixed it.

Exactly. And, and the key thing I also see is when you give that little bit of Lasix, usually I see a small, small dose, and they don't pee, and they're like, oh, I gave it to Lasix, it was too small to even have an effect, but they didn't pee, and therefore Lasix is not effective. Remember, Lasix will not hurt the kidney if they're volume overloaded.

So give a good dose. Get that urine output going, show me they're failing. The thing I like to tell the med students is always Lasix is the threshold drug, so you just maybe haven't found their threshold yet. Exactly, I like that. It is a threshold. And remember, like, increasing it to find that threshold is not dangerous if you clearly see their volume up.

I would say the max for Lasix, when you start getting above 160, you know, if they haven't reached their threshold, then I doubt you're gonna get there alone with Lasix. And so when we call, you know, I generally like to have my list of labs that I'm going to talk to the

consultant about. So I'm thinking like BUN, creatinine, I'm going to have kind of what my current volume status is for the day and then the last couple of days, although we know that can be notoriously incorrect, and then renal ultrasound.

and potentially an echo. Are there any other labs or imaging studies that you find particularly useful to either have or to kind of have working in the background when we call? It depends on how secure in our diagnosis we are. If they're, went into surgery, they had a hypotensive event, And immediately after their cranium starts increasing, hopefully it's clear that the hypotension episode caused AKI.

This is likely ATN. I don't need a whole bunch of lab tests for that. Now, say that they are admitted for a surgery. A couple days before the surgery, the cranium starts slowly increasing by like 0. 2, 0. 3 every day. During surgery goes fine, but it just keeps increasing 0. 4, 0. 5 every day. That might need a little more workup, um, for maybe like interstitial arthritis or something like that.

There's different kind of presentations that would think

different, different workup, but in a case like a general AKI after surgery, like craniate increases by 0. after surgery, definitely I think a kidney ultrasound is a good idea. All urine electrolytes, and I say all, um, you know, like you order a BMP, you get all the electrolytes.

Urinalysis is, is always a good idea. Urine output, like you said, it, it, you know, if it's there, it's super helpful. Urine output alone will make us think, are we going to end up dialysis? patient or not. Like if the cranium is increasing by two points every day, literally the urine output is going to be that deciding factor.

Like, do I need to put a catheter in today or could we wait? And so the importance of getting strict urine output, I can't say how, how important that is. Coming from the surgery side, you know, we have this push, like get that Foley catheter out. Patients out of the OR, get that catheter out so you can get them up and walking, get them home.

You know, the nurses are paging you, texting you, whatever to like get that Foley out for the infection risk. Yeah, I mean, I'm on that same page. Getting the foley out is super important. Like I can,

I can get on that boat. Um, the problem is, is taking out the foley and putting in a Clinton or a tunnel dialysis cat.

That's not fun either. No. And so, and so if you keep that, fully in, like, a day longer, two days longer, three days longer, and that allows us to not put in a dialysis catheter, I think that would be the ideal scenario. Um, but yeah, I agree, like, as soon as a creatinine or kidney function starts leveling off, even starts barely improving, I'm on board with getting that catheter out.

So, you know, we talk about like management of different risk factors to reduce the chances that the patient's going to get an AKI. What are, in your mind, the classic risk factors that set a patient up for a peri op AKI and what can we do to help minimize the chance that they'll get an AKI? Yeah, there's a lot of different, um, like scores out there.

I think like, um, the Cleveland Clinic score, MEDA score, Simplified Renal Index score, all these scores. Say what kind of risk a patient would have going

into the operation and what kind of AKI they would have. In general, being older, female sex for cardiac surgery is an AKI risk factor and then male sex for all other surgeries.

CHF, ascites, high MELT score, hypertension, diabetes, obviously increase preoperative creatinine or having CKD, proteinuria, all that is, is all a risk factor too. Drugs like ACEs and ARBs are recommended generally to hold within a day or two before the surgery, and at least hopefully a day or two after the surgery as well.

Any surgery that's urgent surgery is going to be a higher risk. Any more invasive surgery is a higher risk. And for cardiac surgeries, definitely any longer aortic cross contamination time, bypass time. And also hyperglycemia is a risk. So what can we do to mitigate it? Well, KDGO, which is um, our main society, the Kidney Mean Society, put out a bundle.

They put it out, I think the first one was in 2012, and then like, they redid it, or they

updated it in 2017. But it involves a number of things to reduce the risk. Number one, ACE ARB stops ACE ARB 48 hours before surgery. Uh, two, three, four. Avoid any nephrotoxic agents in the first 72 hours after, which generally means avoiding NSAIDs and aminoglycosides, hopefully.

Obviously, if you're giving aminoglycosides, you're giving something that needs to be given, you know, we have to give it, right? You should be aware that, okay, this aminoglycoside can cause AKI, do I need to give it? Yes or no? And then if the answer is yes, then go ahead and give it. But if the answer is like, I don't really need to give it.

It's better to hold maybe a couple of days after surgery. I think the most important on this K Digo bundle is hemodynamic monitoring. Low MAPS, um, are definitely a high risk factor for AKI. K Digo recommends above 65. Volume assessment after surgery is super important. The main risk is hypervolemic. It has been recommended that they should be leaving

surgery around one or two meters.

Um, positive would be ideal. Obviously if, if they're more positive, that, that is risky because volume overload is a major risk factor for needing dialysis and having AKI. Uh, there's more specific recommendations for each kind of surgery, but it's, it's really in general, we're talking about watching volume status, watching blood pressure and removing nephrotoxins and controlling sugar.

Those are like the main summary of. Things you can do to avoid AKI. Awesome. Thanks, Dr. Tucker. I think that was a super helpful overview on AKI. Couple big take home points for me. Always watch that creatinine. Always watch that urine output. And make sure you know if your patient has a pre renal AKI from hypo or hypervelamia.

And with that, dominate the day.