in this video I will simplify hyponatremia and make it easy for you to understand hyponatremia is a really really high yield topic for exams because so many different disease processes cause hyponatremia and so the test writer can simply give you a lab printout that shows a sodium level of less than 135 and asks you a million different third order questions that challenge you to connect the fact that there's hyponatremia with other clinical features of the disease and again because so many different diseases cause hyponatremia they can ask you about physiology pathophysiology treatment Associated symptoms the list truly goes on forever so you really need to understand how hyponatremia works and what causes it so when you're taking your exam and you see a sodium level of less than 135 the first question to ask yourself is what is my serum osmolality now the term osmolality can be a little bit overwhelming for people osmolality osmolarity serum this urine that sodium here sodium there sodium absolutely everywhere it sounds like a Dr Seuss book but the the fact of the matter is is that these terms don't have to be so scary sounding so when you hear the term osmolality I want you to think how much stuff is in the blood right so you'll see osmolality whether it's serum osmolality urine osmolality that's just telling you where you're looking for this stuff so serum osmolality simply means how much stuff or how much solute is in the serum now that can be normal low or high if it's normal serum osmolality it's called isotonic hyponatremia again this is normal serum osmolality in the setting of low sodium so serum osmolality being normal that's where isotonic comes from and then hyponatremia because you're dealing with sodium of less than 135 if Serum osmolality is low that is termed hypotonic hyponatremia hypotonic meaning low stuff in the serum or low serum osmolality hyponatremia again because all of this is in the setting of low sodium and if Serum osmolality is high that's called hypertonic hyponatremia hypertonic because the stuff in the serum there's a lot of it and hyponatremia again because sodium is low so think through what these terms mean they don't have to be so scary but for most of us they still are now let's start all the way to the left here in isotonic hyponatremia so the three different causes of isotonic hyponatremia are hyperlipidemia multiple myeloma and terp syndrome in the case of hyperlipidemia and multiple myeloma it's actually a really interesting phenomenon here so let's talk about this normally in the plasma you have sodium just floating around and that sodium exists in the aqueous component of the plasma but in certain diseases and in this case in hyperlipidemia and in multiple myeloma you have the production of lipids in hyperlipidemia or the production of proteins in multiple myeloma and when that happens the normal aqueous plasma becomes non-aqueous so instead of this watery plasma if you have hyperlipidemia it's a very fatty plasma if you have multiple myeloma it's a very proteinaceous I hope that's a word proteinaceous plasma and in that case you have increasing levels of non-aqueous plasma so when this happens the sodium levels are still technically the same but more of the plasma is either fatty or proteinaceous and so if we measure that plasma it will appear as though the sodium levels have decreased in reality they haven't changed right the same amount of sodium is floating in that plasma but if it's really really fatty plasma or really really proteinaceous plasma when we measure it it will give us a false low sodium so this is termed pseudohyponatremia and this is one of the types of hyponatremia so if you see hyperlipidemia or multiple myeloma don't be surprised if on your exam the lab printout shows you hyponatremia yes sodium is measured as low but no it's not actually low this is pseudo hyponatremia now in terp syndrome this is kind of interesting so terp is transurethral your transurethral resection of the prostate it's a type of surgical procedure done to correct an enlarged prostate and in this surgery what they do is they're squirting water at the area that they're dissecting or that they're resecting rather and when they do this there's so much venous sinus there there's so much surface area that can absorb that water that you actually get a dilutional hyponatremia so in terp in transurethral resection of the prostate that can cause subsequent to the surgery low levels of sodium because all of that water is being absorbed through that venous sinus during the surgery so causes of isotonic hyponatremia hyperlipidemia and multiple myeloma which again is is a pseudo hyponatremia and terp syndrome which is sort of a dilutional hyponatremia now the way to memorize this isotonic so remember ISO ISO eye for immunoglobulins in the case of multiple myeloma s for saturated fat in the case of hyperlipidemia and O for operations in the in the case of terp because that's an operation it's a surgery so these are your causes of isotonic hyponatremia now let's go all the way to the right we'll talk about hypertonic hyponatremia the causes of hypertonic hyponatremia are hyperglycemia Mannitol and radio contrast use and the way that this works is pretty simple but let's just walk through it so that it makes sense so here is a blood vessel and in that blood vessel you can have glucose you can have Mannitol or you can have contrast right you can have glucose because we all have glucose and some of us have too much of it you can have Mannitol if Mannitol is being used in treatment or you can have radio contrast if the person is getting contrast for some type of radiology study now when glucose or Mannitol or con contrast is introduced doesn't matter which of the three we're talking about there's more stuff in the blood vessel and when water sees more stuff water wants to flow and follow that stuff that's just how water works so water comes on in and in this case water dilutes the amount of sodium and therefore you get hyponatremia so again hypertonic hyponatremia hypertonic meaning there's lots of stuff so we've got lots of glucose in the case of hyperglycemia where lots of mannitol or lots of contrast but we have low levels of measured sodium so sodium is low because water is following all that stuff that's why it's hypertonic and that causes the sodium to be low so the way that you can remember this is hypertonic you get hyper from stuff you can drink you can drink a lot of glucose you can drink a lot of mannitol Mannitol is really just a sweetener or you can drink contrast if you're getting a radiology study so you get hyper from stuff that you can drink you can drink sugar you can drink sweetener you can drink contrast that is hypertonic hyponatremia now the last category here is hypotonic hyponatremia and I saved this for last because this is the most confusing and it has the most causes so when you're dealing with hypotonic hyponatremia hypotonic means not a lot of stuff and it's hyponatremia because even though there's not a lot of stuff in the serum sodium is still measured as low so the next question that you have to ask yourself if you're dealing with hypotonic hyponatremia is what is my volume status and volume can be hypovolemic low volume uvulimic normal volume or maybe slightly elevated or hypervolemic high volume now I'm going to go to another slide and prop this up to the top because I'm running out of space so now we're talking about hypotonic hyponatremia and we assess our volume status so let's start all the way on the left hypovolemic if we're hypovolemic that means we have a low extracellular fluid volume and there are lots of different causes here so vomiting diarrhea dehydration Burns and bleeding these are all extra renal causes of hypovolemic hypotonic hyponatremia I know that sounds like a lot but let's simplify here so these are extra renal causes which means they are causes that happen outside of the kidney so our volume is low right we don't have a lot of fluid in under what situation would you not have a lot of fluid that has nothing to do with the kidney well vomiting up that fluid pooping out that fluid never getting that fluid being burned or bleeding and losing that fluid through other mechanisms these are extra renal causes of hypovolemia low volume all right now if the cause is hype is is extra renal our una which is our urine sodium will be low think about it the urine sodium will be low because you're losing the sodium you're losing the electrolyte with the loss of the fluid so the way that I want you to think about this is that even though this isn't physiologically correct per se when the fluid is lost you're losing the sodium with it and so if Downstream in the kidney we were to theoretically measure the urine sodium that would be low because the sodium never makes it to the kidney because you're losing it Upstream of the kidney with the loss of the fluid I.E you're throwing it all up hooping it all out Etc so in extra renal causes of hypovolemic hypotonic hyponatremia urine sodium is low because the sodium is lost with the fluid and never makes it to the kidney now let's contrast that with renal causes of hypovolemic hypotonic hyponatremia so the renal causes include taking certain medications like ACE inhibitors or diuretics Addison disease cerebral salt wasting syndrome and ATN acute tubular necrosis in this instance these are renal causes of hypovolemia so this is renally related fluid loss and when we have renally related fluid loss our urine sodium is elevated that fluid is lost through the kidney and so if we measure the urine sodium that's going to appear relatively High so to be clear extra renal causes and renal causes in both cases you're dealing with low sodium you write hyponatremia in both cases you're dealing with hypotonia right low serum osmolality how much stuff there is is low in both the only difference here is whether urine sodium is low in the case of extra renal causes or if urine sodium is elevated or normal in the case of renal causes so here are two examples of a lab printout you could be given when you're taking your exam again the point I'm illustrating here is that sodium and serum osmolality will be the same value whether we're talking about an extra renal cause or a renal cause what you need to be on the lookout for on your exam is the value of the urine sodium so up top if theoretically you were given this example where urine sodium was low at 12 that would indicate an extra renal cause of hypovolemic hypotonic hyponatremia but at the bottom of the slide if you were theoretically given a value of urine sodium that was greater than or equal to 20 which could either be normal or increased this would indicate a renal cause of hypovolemic hypotonic hyponatremia so take away from this slide is that you're only going to be given a different value for urine sodium that value of urine sodium will determine whether you have a renal or extra renal cause of hypovolemic hypotonic hyponatremia so I hope that's clear now that was the most complicated part of this entire video so if you're okay with that let's move on and it'll just get easier from here so going back to volume status if we have a normal ECF volume so we're uvulimic the causes include SI ADH hypothyroidism psychogenic polydipsia adrenal insufficiency medications that can technically cause SI ADH so I would consider those iatrogenic but you could just as easily group that in with the first SI ADH thing that I put there and lastly beer podomania so in these examples of uvulimic hypotonic hyponatremia we just have limited free water excretion so in all of these instances the body is retaining a little bit more water than it's supposed to it's still technically uvulimia right we have normal ECF volumes we just can't excrete that free water as well and so in this instance because we cannot excrete that free water as well we have hyponatremia we're hypotonic but we're euvolemic so these are all the causes that you want to know the biggest one here by far is siadh if you see SI ADH it's uvulimia so know that that falls into this category the last category and probably the easiest to conceptualize and understand is the hypervolemic category so when our volume status is hypervolemic but yet we still are hypotonic and hyponatrimic the causes that you want to think about are anything that causes really severe fluid overload so congestive heart failure cirrhosis nephrosis or end-stage renal disease now there's a little Nuance to this and end-stage renal disease you should know when you're at that end stage it would fall under hypervolemic because the kidney is so damaged and so severe that the body just unfortunately has no way to excrete all of that free fluid but at varying other severities of kidney disease when it's more acute or as it is progressing it could technically fall into the hypovolemic or euvolemic category because of that Nuance I don't think that you need to know the difference I don't think the test writer can really ask you that that's really sort of beyond the scope of board exams or tests in general but just know that end-stage renal disease you know it's so severe that the volume is stuck in the body because the kidney is completely shot that's hypervolemia anything else I would say don't worry about but the takeaway here is that hypervolemic states are fluid overloaded causes so CHF cirrhosis nephrotic syndrome and end-stage renal disease and that's it if you're able to understand everything that I've talked about through this point of the video you understand hyponatremia