Episode Transcript
Hi and Welcome to Clerkship Ready - Pediatrics - A podcast aimed at helping you excel during your clinical clerkship in Pediatrics.
I am Dr. Lisa Hainstock, and I am an Associate Professor of Pediatrics and pediatric hospitalist at the University of VA Children’s Hospital.
Today, we will be reviewing fluids and electrolytes. This podcast is focused on helping you feel prepared to order fluids and replace electrolytes on the patients you are taking care of on the inpatient pediatric floor.
During your pediatric rotation, you will quickly realize that we take care of a varied group of patients both in age and size and then of course you must consider their diagnosis. The vast majority of our hospitalized patients require supplementation with IV fluid and/or electrolytes during their hospitalization. It is absolutely paramount that you are cognizant of the fact that IV fluid, while it might seem fairly trivial and easy to order, it should be considered a medication. For that reason, you need to be thoughtful as to how to place these orders in each clinical context. It is not a one size fits all.
Let’s start by reviewing some basic considerations that will be important for you to think about as you are ordering the fluids for your patient. Your patient’s fluid needs will be based on maintenance fluid needs, your patient’s current fluid deficit, and predicted ongoing losses.
Let’s start with maintenance fluid needs. Maintenance fluids contain three components: water, electrolytes- such as sodium, potassium, and chloride-- and glucose. The goals of maintenance IV fluid are to prevent dehydration, prevent electrolyte disorders, and prevent ketoacidosis. Maintenance IV fluids do not provide adequate calories for proteins, fat, minerals, or vitamins. The Holiday Seger method is a well-known calculation to help guide your initial maintenance need for parenteral fluid therapy. This method was published back in 1957 and is still utilized widely today.
Many people will reference this as the “4-2-1 rule.” Essentially, for the first 10 kg of your patient’s body weight you will order 4 mL per kilogram per hour of your fluid maintenance rate. For the next 10 kg of your patient’s body weight, you will add an additional 2 mL per kilogram per hour. For each additional kilogram over 20 kg you will add 1 mL per kilogram per hour to the patient’s fluid rate. Take a moment to calculate what the fluid rate would be for a 35 kg child [pause]. So for a 35 kg child the first 10 kg would equal 40 mL per hour, the next 10 kg would add 20 mL per hour and the final 15 kg would add an additional 15 mL per hour totaling 75 mL/hour[RYM1] .
Children over 65Kg do not need the same incremental dose and should cap at about 2.5L per day or ~100 mL per hour.
It is incredibly important to remember that this calculation includes several assumptions about maintenance fluid. It assumes average insensible losses, average energy expenditure and metabolism, average urinary losses, no additional losses from other site, and normal renal function. You can imagine why following this formula without any flexibility could be problematic--The vast majority if not all of our patients do not fit into any of these “average” categories.
Let's pretend you are seeing a patient in the emergency department and are preparing to order their maintenance fluids. There are two important age groups to remember. The patient under 28 days and the patient 28 days to 18 years of life. The American Academy of Pediatrics recommends different maintenance fluids for each of these patient populations. For patients under 28 days, the recommendation is to use D5 ½ normal saline, and for patients 28 days and older the recommended fluid is D5 normal saline. The D refers to the dextrose component or the glucose or sugar so again your patient does not get hypoglycemic, D5 is 5% dextrose and the standard glucose concentration for maintenance fluids. The decision to add potassium can be made based on whether you think your patient is at risk for hyperkalemia or has renal insufficiency. If your patient is not at risk for hyperkalemia, you can add 20 mEq per liter of potassium chloride to your patient’s fluid orders.
Stepping back for a moment, before you even order maintenance fluids, it is a good idea to consider whether your patient is dehydrated, is at risk for ongoing losses, or has concern for sepsis or hypovolemic shock. (Noting of course that the last two of those scenarios are the most concerning). In these scenarios, it is a good idea to consider ordering a fluid bolus before you initiate maintenance fluids. A bolus is different than maintenance fluid in that it is given over a shorter period of time—typically 10-15 minutes. It is meant to quickly replete their fluid deficit. This[GS*2] next point is incredibly important. You must always bolus with isotonic fluids. Never bolus with a hypotonic fluid such as half normal saline or quarter normal saline. You do not want to iatrogenicly induce hyponatremia and potentially make your patient much sicker.
The two options for a fluid bolus are Normal Saline and lactated ringers. Lactated ringers has a slightly different composition than normal saline. While normal saline contains just sodium and chloride, lactated ringers contains lactate, which can serve as a buffer for your patients with acidosis. It also includes a lower concentration of chloride than normal saline and includes a small amount of potassium. We will talk more about potential uses of LR again in a bit. In general, your fluid bolus should be 20 mL per kilogram. The exception to this is a patient who might have cardiac insufficiency, in which case you would use a smaller bolus of 10 mL per kilogram. Always remember to reassess your patient after each bolus. If you feel your patient is still dehydrated, you should absolutely consider ordering an additional one or two boluses of 20 mL per kilogram, reassessing after each bolus. These fluid boluses should be given over 15 minutes.
Back to LR--You can also use LR as maintenance fluid (rather than D5NS) One of the scenarios that I love to use lactated ringers for maintenance fluid is for the patient with diarrhea. As you may remember, patients with diarrhea often have a non-anion gap [RYM3] metabolic acidosis. Sometimes, clinicians will order fluids with sodium chloride for these patients, including multiple fluid boluses. What can start to happen is that when they receive too much chloride, their kidneys start dumping bicarbonate. Then on morning rounds when you are looking at their basic metabolic panel or BMP, you might feel confused as to why you did such a great job hydrating your patient, but now their HCO3 level has actually dropped from 12 to 6 and their chloride level has increased from 103 to 117. This is more than likely due to an abundance of fluids with normal saline which as you recall contains more Cl. In these instances, I prefer to use D5 with lactated ringers. [RYM4]
Let’s pause to learn some fun facts about how lactated ringers got its name. The solution was named after a British clinician, physiologist, and pharmacologist named Sydney Ringer. He was born in 1835 in Norwich, England. He is probably most famous for his work creating the solution ringers lactate or lactated ringers. He was able to demonstrate --after much trial and error-- that this solution would enable a beating frogs heart (outside of its body) to sustain muscle contractions for the longest period of time. Not an experiment I would necessarily want to be involved in but thank you Sydney Ringer for your research[RYM5] .
The next thing I want to briefly touch on is the role of antidiuretic hormone in the hospitalized patient. As you may recall, this hormone is responsible for increasing the reabsorption of water into the circulation from filtrate in the kidney tubules. There is an entity called the syndrome of inappropriate antidiuretic hormone, or SIADH, which can result in hyponatremia. I mention this, because almost every one of our children who is hospitalized is at risk for SIADH. The list of patients at risk includes those with pulmonary disease, such as pneumonia, central nervous system disturbances, such as meningitis, malignancies, medication-- such as opiates and some antiepileptics-- postoperatively, and even just pain and stress. From this list, is it easy to see why nearly every single one of our patients is at risk for SIADH. This is yet another reason why it is important for you to carefully consider your patient’s need for IV fluids every single day.
Next, we will talk a bit about what observations you can make to determine your patient’s level of dehydration. After that we will walk through a few practical cases. The very first thing you should be assessing when you walk into the room is your patient’s mental status. Is the patient awake and playful or are they a wet noodle as I like to say-- lying there without much activity. Then I would do a careful physical exam- assessing the patient’s mucous membranes, skin turgor, pulse rate and quality, capillary refill, and presence or absence of tears. A few other questions that you can ask to ascertain your patient’s level of dehydration is asking caregivers about urinary output[GS*6] simply by asking “how many wet diapers have you changed today?” And one that clinicians very often forget, simply ask parents for a baseline weight. Being a parent myself, I can tell you that most parents absolutely can tell you their child’s weight within a very small margin. If your patient is between 3 and 5% down from baseline weight that would likely be considered mild dehydration. If your patient is 10 to 15%, down from baseline weight, I would consider that to be severe dehydration. Of course all of the other physical exam findings should be considered as you assess whether your patient is mildly, moderately, or severely dehydrated. I do want to add a quick note about skin turgor. In your patients with severe hypernatremia, you can be fooled by how well their skin turgor looks. This is because the water is preferentially entering the intravascular space, making your patient’s capillary refill and overall skin turgor and appearance look much better than the labs reveal.
Let’s pivot for the next several minutes and go through some case scenarios involving some common electrolyte abnormalities you may encounter during your rotation. The first case is a 12-year-old who is hospitalized with influenza and you are called with a critical value. The nurse states at your patient’s potassium is 7.7. What are your next steps? The obvious first thing you should do is go to the bedside and assess your patient. What you should not do is assume that the potassium is hemolyzed[GS*7] (meaning that the red cells have been lysed and have released some intracellular contents, including potassium. You should not ignore it or just recheck it and go on with your work. When you go to the bedside, you should immediately put the child on the monitor and order an EKG. Now think about what you might see on the EKG if your patient is hyperkalemic. Findings might include peaked T waves, long PR interval, wide QRS, or depressed ST segment. So now you are at the bedside and you are seeing an EKG with many of these findings. What are you going to do next? First of all you should think about your patient’s medications and fluids. Eliminate all exogenous potassium from your patient’s fluids and be sure to hold any potassium sparing medications that they are receiving[RYM8] such as spironolactone and ACE-inhibitors such as Lisinopril or enalopril. Then you have a few options. Most common of these options is administering calcium gluconate. The dose of calcium gluconate is 100 mL per kilogram over 3 to 5 minutes. I do not expect you to remember the dose, but you should be able to remember the medication. Also know that you can repeat this dose in 10 minutes if your EKG fails to normalize. During this time you should also be checking serial potassium levels.
Another option to manage hyperkalemia is to give insulin with D 25. This is a bit trickier as it involves monitoring blood glucose levels. In my practice, I typically give calcium gluconate. There is an option to give sodium bicarbonate IV over 5 to 10 minutes as well, which might be a helpful alternative if your patient is also acidotic.
Let’s think about the scenario where this patient with the potassium of 7.7 does not have an IV. Is there anything that you can think of that might be an acceptable medication to help? Here albuterol might be helpful, as it is typically very accessible, and will drive the potassium intracellularly. Which brings up the next point. All of the aforementioned medications do not decrease the total body potassium. They merely drive the potassium intracellularly. So you still need to address the excess potassium. In this instance, I prefer utilizing loop diuretics such as furosemide. The dose is 1 mg per kilogram. You can also consider a cation exchange resin, such as sodium polystyrene sulfonate, which you may better know as Kayexalate, however, this is contraindicated in infants, and any child who has gut motility issues.
I want to share a pneumonic which may be helpful for you to remember how to address hyperkalemia. It is C big K drop. C as in the letter, the word “big” then the letter K and “drop”. The C is for calcium gluconate. The B Is for bicarbonate, the I and the G are both for insulin and glucose. The K is for Kayexalate and the drop is for dialysis. Noting that dialysis is reserved for patients with renal insufficiency who do not respond to medical management.
Another question that also often comes up is – is there a level at which I should be more concerned about hyperkalemia and its effects on the cardiac membrane? The answer is yes. In general potassium levels less than seven will not be associated with adverse events, but if your child’s potassium is between six and seven and they are at risk for continuing rise of potassium, such as rhabdomyolysis or tumor lysis syndrome, I would still be at high alert for sequelae from hyperkalemia.
OK next case. A parent calls you concerned that his child recently started eating power cords. What do you tell him? Depending on the current situation at home you may need to ground him until he can conduct himself appropriately[RYM9] .
OK next case for real now. You are admitting a two-year-old with severe malnutrition and failure to thrive whom you suspect is suffering from medical neglect. He appears malnourished but is well hydrated. As you begin the process of providing nutrition, you are astutely checking labs. What specific lab abnormalities are you looking for? I want you to think about what happens when you are feeding a child who has not received nutrition in what you believe is quite a long time. Here you would be thinking about your patient’s risk for refeeding syndrome. This syndrome causes electrolyte and fluid shifts after re-introduction of [RYM10] nutrition in malnourished patients. These fluid shifts may result in low potassium, low phosphate, and low magnesium. The mechanism by which this happens is that when insulin is released, these electrolytes move intracellularly thus decreasing the intravascular concentration of each. In addition, your patient will start making more ATP, which also utilizes greater amounts of phosphate and results in a risk of hypophosphatemia. In addition, when insulin is released, it automatically causes fluid retention. You can imagine why this might be problematic in a patient with weakened cardiac muscle due to prolonged malnutrition. A greater amount of afterload to pump against could cause real problems with your patient’s heart function. Pediatric patients at highest risk for refeeding syndrome include those who had prolonged periods with nothing to eat-- considered greater than five days-- severe anorexia nervosa, and malnourishment due to chronic disease such as malignancy.
Your patient will be at highest risk for refeeding syndrome during the first 3 to 5 days that you are providing nutrition. During this time, it is important that you provide slow re-introduction of nutrition, with close monitoring of the aforementioned electrolytes. Let’s walk through another scenario that you may encounter in a patient with concern for refeeding syndrome.
You have been checking labs on the two-year old mentioned a few minutes ago. On day four of admission the potassium is 2.9. What do you want to do? Recheck, replace orally, or replace IV? Also consider what medication you would order as replacement. In this scenario, I would order oral KCl, since I know that this level is already low and likely to drop further. If this was a patient who was otherwise looking well and I did not have concerns for continued losses, I would feel comfortable watching the K levels. I typically reserve IV replacement for potassium levels less than 2.5, especially if they are at risk for ongoing losses or have other electrolyte abnormalities such as Mg or Ca which might affect cardiac conduction.
Before we close, I will share some additional clinical pearls that will be helpful during your time on the inpatient pediatric service:
There is an association between calcium and albumin. More specifically, if your patient’s albumin is low, the serum calcium will also be affected. This occurs because less calcium is bound to albumin which will then lower the measured level (even though the physiologically important portion—the ionized Ca is often normal). You can estimate the actual calcium level by multiplying 0.8 *your patient’s albumin. You then add this to their measured calcium. So if your patient’s albumin is 2 and the calcium level is 7, you take 2 * 0.8 which equals 1.6. Add that 1.6 to their serum ca which is 7 and you get 8.6. Remember this is just an estimate. If you want a more accurate level, you can check an ionized calcium.
There is also an association between potassium and serum pH. If your patient is acidotic, the potassium will measure high as it moves extracellularly. Conversely, if your patient is alkalotic, the potassium will measure low as it moves intracellularly.
Today we talked a lot about fluid choice, maintenance fluids, and managing dehydration. We also reviewed a few high-yield cases that should be helpful as you start your clerkship. When your attending asks you how you want to manage dehydration or hypokalemia, you will be ready to confidently state your plan!
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