The next one again, we have Dr. Basu, who is going to speak about fluid electrolyte and acid-base disorders. You guys doing okay? Yeah, kind of? It's always horrifying hearing the world's best anesthesiologists say, game over. Okay, my heart skipped a beat there. Thanks for that, Sapna, I really appreciate it. So I realize right away that following Sapna and a very interesting and engaging topic with the lecture that everyone wants to skip every year is not the best thing in the world. That's okay, we will get through this, it'll be fine. So I'm going to talk about fluid electrolytes and acid-base balance, except for the fact that I'm actually going to largely skip acid-base interpretation as that is something that would be kind of insulting for me to talk to you about. We will just harken back to it at the end a little bit. And before I get started, Jerry, I think that was a dig on kidney function? I took that personally somewhere in your talk, you know? That is true. That's also true. True, true, unrelated. Okay, here we go. And the other thing is Nick Ettinger's recorded talk on this topic is fantastic. So that is actually really worth listening to. What I'm going to do is more of a cursory run-through, primarily of kind of the major drivers of electrolyte imbalance and how to think about it for the exam itself. So the key points to take away, you do need to know the composition of body fluids and parenteral fluids that we use in resuscitation and in maintenance therapy. It is important to understand the regulation of the key electrolytes in homeostasis. And then, like I said, we're just going to briefly touch on acid-base balance and then get you to some coffee this morning. This is not surprising to anyone. This is something that showed up first year of medical school, first day of physiology. This horrific box plot thing, I hate it. This is not going to be asked, this whole idea of interstitial fluid compartment, interstitial fluid space. This is all theoretic. It is, however, very important to understand, particularly as you teach trainees, about the difference in water composition as you get older. So the left side of the fetus to the elderly person, diaper to diaper, you understand percent of water in the human body. So do not memorize the percent fluid in the interstitial spaces, but the practical way to think about it and following an anesthesiologist, this is really important, is volume of distribution and understanding total body water. So it goes down from birth to 12 years. Total body water is about 80% when you're a newborn, and then it goes down steadily until you're about adult physiology, which is around 11 to 12 years old. My first boss, Hector Wong, would always kind of point this out, that an 11-year-old is an adult, which raised a lot of eyebrows, but it's kind of true. The majority of the fluid is intracellular, minority is intravascular in the younger age. A good example, a 10-kilo, 12-month-old has a total body water of about 7.5 liters. A 50-kilo, 5-year-old has a total body water of 30 liters. Body composition and medications, the volume of distribution is something you have to know. So I do have a slide that has some of the basic math, which will likely show up in some shape or form on the two to three questions that are about electrolytes specifically. But volume of distribution is something that is very practically testable and actually usable at the bedside. So remember that if you have a dose of 5 milligrams, and then the concentration of the drug in the system is 1 milligram per liter, then necessarily the volume of distribution must be 5 liters. So it's cut dose over concentration. When we think about the way to think about percent volumes and everything, albumin is the best way to think about it. This is a practical thing at the bedside also. 25% albumin is 25 grams in 100 mLs. So this percent water volume is analytical chemistry. That's what might be one of the three reasons we took it. But just remember this, okay? So 25 grams is 10 mLs of 250 mLs of 25%. So you will see this show up in some variable form. As Jerry mentioned yesterday, we are moving towards more blood product and colloid-based resuscitation. Crystalloid solutions, balanced salt and electrolyte, form a true solution, passes through semipermeable membranes. Depending on your institution, this is another thing to understand from your friendly pharmacist. What do we have in stock? Do we have things like 7.5%, 23%? A lot of places don't. Adult ICUs do, if that was ever the need. Most everyone has 3% hypertonic. Then of course there's the devil juice, normal saline, which is not normal by any standard. There's lactated ringers, so lactate instead of bicarb for stability. And again, lactate is converted to bicarbonate in the liver, and it's closest to serum. The reason that I would point out to all of you that normal saline is highly AB normal is that this is the publication that propagated its use. It's very small. It's by Will O'Shaughnessy in The Lancet in 1831, which explains that in the time of cholera, he mixed together a scruple of this and a scruple of that and decided to give it to his dogs, and it worked, and then he tried it in humans, and it worked, and he begged for it to be published in The Lancet, and it was. So if you want a Lancet publication, write a letter that says you're obedient servant, and it will get in. But for this reason, this has been propagated because it turned blue and purple people into pink people, not because it actually is good for you. So fluid deficit assessment, the table itself is something that will not be directly assessed. What percent dehydrated is this patient? No, no, no. But it is important as you navigate this as a clinician to understand what is the sodium deficit, what is the water deficit. So the way to think about an H2O deficit is this formula at the bottom, 4 times your weight times the serum sodium minus 140. Easy to remember, easy to think about in how you distribute it. Blood products. So these are not kind of very surprising to anyone. It is important to know how long your local lab stores blood. That is not something that we generally ask, although it does affect the stability of the blood and the pH and all this other stuff. Out of curiosity, this is good to know. Sometimes this shows up. What is the pH of stored blood? What is the ionized calcium in a bag of blood? It is very low because it is stored in EDTA, so calcium is chelated out. The pH of stored blood is somewhere in the 5 range, 5 to 5.5. And so that is why it is important to ask your blood bank how long do you guys store your blood. Most of the time for resuscitation or for massive transfusion, they will use kind of the freshest blood. That does not mean that the blood is bad if it is not beyond seven days. What is the difference between FFP and frozen plasma? What is the INR in a bag of FFP? These are all things to know. So 5 to 5.5 is the pH of stored blood. The ionized calcium in a bag of stored blood is 0.2 to 0.25. And it is cold. So think about massive resuscitation when somebody comes in with inflicted trauma or gunshot wound or TBI or whatever it is. You are resuscitating with cold acidotic hypo calciumic fluid. If you are a surgeon, that makes your head explode because these are the things to avoid in the death spiral of the 3Ts of trauma resuscitation. You do not want those things. When we inherit these kids after the emergency department, the things that we forget about are the fact that the clotting factors, the coagulation factors, the calcium, the temperature in the blood that was just given all dilutes everything out. And this goes back to the volume of distribution. So practically speaking, know what you are giving. So if you are giving, for instance, FFP because the INR is 1.8, good luck getting it down. It is not going to work that well. So this could be on your test. So Dr. Zimmerman did speak of DKA. Burn is easily testable. There usually is a question about burn. And you need to know the modified Parkland formula. Who knows why Parkland Hospital is very famous? Yes, that is where they took JFK, right. Also the burn formula. So the modified Parkland is 2 liters per meter squared of body surface area and then 5 liters per meter squared of your total burn surface area is the total amount of fluid you will give in 24 hours. And you are going to give the first half an 8 and the second half in the following 16. Here is a good example. And remember, the first degree burns, this will come up, right, they will say, oh, first degree is cover a certain percentage. That is not part of the formula. So the case example that sometimes could show up, you have a kid who is just under a meter squared. This generally is someone who is a 1 to 2-year-old, 20 kilos, total burn surface area is 25%. So that means that your total, the total burn surface area is actually 0.2 meters squared. When you do the math, it is 1.6 liters plus 1 liter, so you have 2.6 liters in the 24 hours that you need to give. So you divide that in half and there is your math. Does that track? So that formula is very important to remember. Yes? Yeah, that is a good, Analia, what do you think? I mean, I know we have shifted. We don't know. That is very helpful. Good luck. No, I mean. But most likely they will say, they will give you a case and they will say calculate the amount of fluid they are going to give. Yeah. And I don't even know if they have to calculate to that detail, but they will ask you, you know, how much you gave in the first, you know, eight hours and what do you do. I don't think it will be. Again, we don't know. Where are you saying? Yeah, so if you have access to study banks that go from 2002 every two years, you will see kind of a trend in how that changes and the most recent ones are more of the modified part. So, I don't know. I think when you get a burn question, it is going to be very obvious. It is not going to be a subtlety about the differences. It could just be kind of that half in the first state, second half in the next 16, that kind of thing. But, you know, if they talk about second and third degree, it is going to come up like that. Yeah, go ahead. One thing that will also, that is important in this one is your recitation, like your eight hours start from the time of the burn, not from the time that you start. Right, right, right, right. Yeah, yeah. Okay, and then Dr. Zimmerman talked about DKA, but the understanding the correction for hyperglycemia when you are looking at your serum sodium is something that you have to know. And most of us dealt with this in our residency training. But, again, as you go through and you go through your fellowship and your early attending years, some of this stuff kind of glazes over. But this is very easy to remember and easily testable. This is generally not going to be on your boards, but this is near and dear to my heart, so I have to mention it, right? So, in practice, we have a couple trials that are in development now for proper fluid management trial. Yet, we don't know really how we practice. And contrary to popular belief in training, you know, a bowl is the mother's milk equivalent of 20 per kilo is not appropriate for everyone, as you know. These are three different pictures from different papers that you just have to know. So, the first is Stacy Valentine's study from a while ago comparing the FACT trial, the fluid and catheter treatment trial in adults, to a pediatric arm of an ICU cohort showing that the topmost curve is that our kids tend to accumulate more fluid over time per body weight. The bottom is Scott Sutherland's paper looking at fluid overload percentage at the time of CRT initiation and the y-axis is mortality. So, I will say that the needle has already moved. Recent data from the We Rock Collaborative shows that time of percent fluid overload at time of CRT initiation has actually come down. More of you are very aware that, hey, we should be starting CRT or we should be thinking about it before the belly button sticks out, right? You don't need the turkey baster to come out. So, people think about that. And then the meta-analysis that we published in JAMA a couple years ago about fluid accumulation. Just be mindful of it. Make it a part of your practice. That's my soapbox for this. So, electrolyte, the normal balance, and we'll kind of quickly go through electrolyte stuff. And again, this is where Nick's lecture is very helpful because he dives into each of the electrolytes, primary aberrancies, and case examples. Just remember that, you know, the primary electrolyte in your body, the primary electrolyte which differentiates us from frogs is sodium. And the sodium composition in your different body fluids does vary considerably. There will not be a question about diuretic mechanism. But in practice, this is fundamental to what you do. Just remember that as sodium is the principal cation in your system, it governs phase one action potential. So, myocardial action potentials do show up. But that phase one depolarization of hitting threshold to go and start the myocardial sequence is really important. This is also why when you have ingestion show up for tricyclics and things, sodium bicarbonate is the antidote because it resets the threshold. That sometimes does show up. Sodium drives the balance of nearly every other solute. The control mechanisms are multiple. But just remember that when we generally tend to influence sodium regulation, it's through natriuresis or we give sodium. But natriuresis is a luminal side phenomenon, meaning that it's not in the blood. It's in the tubular lumen of the kidney. So, you give Lasix. It doesn't work in your wrist or wherever it is. It has to be transported to the P side of the kidney. And it works on the P side, not on the blood side. So, why is that exquisitely important? It's because it all depends on the countercurrent mechanism of sodium and chloride gradients. When we have kids in reality who are critically ill, the sympathetic tone, hypoaldosterone tone, hypoaldosteronism all are thrown off. So, our sodium regulation is also thrown off. ADH increases to retain water. Sympathetic innervation and activity will drive sodium resorption as a protective mechanism. And there's work being done right now about looking at renin levels and angiotensin 2 and aldosterone. Jerry went through this about critical illness and dysnatremia, so I will not. But just remember that acidosis is actually very, very impactful to sodium regulation. Why? Because, again, the primary enzyme in our body that helped us emerge out of the water, which is sodium potassium ATPase, is extremely pH sensitive. So, that disassociation of that enzyme happens around 71572. So, if you have a kid who's acidotic, your overall bioenergetics will suck. So, you need to get through that system and make it work. But acidosis impairs sodium potassium ATPase. It's unable to move against concentration gradients. Here are the electrolyte math that will in some way show up. So, we all can calculate serum osmolarity and calculate osmolar gap. Make sure you know how to calculate osmolar gap. That is very, very testable. That is very, very easy. Do not miss easiness. Fractional excretion of sodium, which is the reason none of us wanted to do internal medicine and do rounds on internal medicine, sometimes shows up. Ah! So, it does help to know that. Sodium deficit and free water deficit goes back to that formula that we talked about for free water. But sodium deficit, this is a great question for residents when you are the attending on service. But it is good to know, right? So, this is not going to, you know, kill you through this math, but it is important to know. Potassium, chloride, bicarbonate, as they call them, the ionic players. Remember that acidosis increases hyperkalemia. Acidosis also should increase your ionized calcium because it disassociates from albumin. Normal calcium, normal ionized calcium in the face of acidosis is AB normal. So, that is the practical aspect of at the bedside. And Jerry talked about DKA. And this is, this will not be on the boards, trans-tubular potassium gradient. However, we throw it on there because this is an electrolyte talk. Sapna did talk about some of the other kind of medicines including, you know, succinylcholine and effects on potassium. But I do think that these, the iatrogenesis imperfecta on what happens with potassium with the other meds is something to pay attention to. So, as you give things like insulin, as you give things like immunoglycosides, as you give things like beta blockers, just remember the effects on potassium. And we're going to go to this real quick. So, this is, I think this is one of the final ones. So, just remember in terms of serum bicarbonate, serum bicarbonate is calculated on a blood gas. So, when you are interpreting a blood gas, have your mechanism of going through the context of the patient. Where is the sample from, obviously? Is this, what is the pH? And then get through your algorithm. We're not going to go through examples today. And I do not think that interpretation of the blood gas is going to be a board exam question for you, right? It's going to be what's the context of the patient. Just remember there are four factors that affect bicarbonate reabsorption. Concentration in the lumen, your urine flow rate, and your arterial PCO2 are the main ones. And then angiotensin too. And so, this is the whole acid-base slide that I have for you. ABG is more accurate. Venus is mixed. Figure out your pH. Remember your serum bicarbonate is calculated from your pH and PCO2. And the base excess and deficit definition is the amount, the stoichiometry that's involved in adding acid or base to a blood sample to get it to 7.4. Okay? So, that is a correction factor that is not actually the amount of base in your blood or amount of acid in your blood. How much time do I have? Oh, I do. I don't think anybody wants me to have the time. So, we're not going to talk. The thing that is the attending level discussion is strong ion difference, which is not testable. But this stuff is, gap acidosis, the effect of this whole, like, mud piles and going through your algorithm. But again, integrate your clinical context and think about that. And that's actually my last slide. So, the things that I did not talk about, one of the things that is very easily testable is refeeding syndrome. And I think Katri or someone else will talk about this in nutrition. But the reason it's relevant is for hypophosphatemia. So, hypophosphatemia is probably one of the most under-recognized electrolyte abnormalities in our hands. Hypophosphatemia is directly associated, as you can imagine, with bioenergetics. But so many of our kids in critical illness states are hypophosphatemic. And we just kind of glaze over that in favor of more, you know, exciting electrolytes. It's also very true in the next talk I'll give on CRRT that hypophosphatemia and calcium abnormalities are the two that we tend to glaze over while we're working on fluid and sodium. So, again, I would say take the time probably a week, one week, before you take the exam and listen to Nick's lecture. Because it'll kind of bring it back to mind real quick. Don't spend time before that, because then you'll get lost. Thank you guys for providing your email addresses. Well done. Awesome. All right. I think that's it for me.

fluid balance

electrolyte regulation

acid-base disorders

sodium and potassium

critical care

refeeding syndrome