Another case of hyponatremia...bloopers and all!

Drs Ambruso, Blaine and Young review a case of an elderly woman who is admitted to the hospital with hyponatremia.  They slowly take the listener through distinguishing between hyponatremia from too much water consumption vs inadequate solute intake vs SIADH.  

Sophia Ambruso DO @Sophia_Kidney, Sarah Young MD @kidneycritic, Judy Blaine MD, Parisa Mortaji, MD

Transcript

KIDNEY ESSENTIALS PODCAST SEASON 1 EPISODE 2

PRESS RECORD

1,2,3 clap

Welcome to Kidney essentials

A podcast for Medical students, residents, and advanced practitioners at the University of Colorado and beyond

Introductions: 

Judy ,Sophie& Sarah

Name/Our institution/Areas of interest/ NO COI statement / twitter handle

 a few Housekeeping notes BEFORE our next case

Please check out our mini podcast  bonus episode where we go go over a mistake we made in our first podcast:

Mission statement (Sophie):

• Make nephrology more accessible, less intimidating
• Provide concise nephrology “pearls” in each episode to help listeners understand renal pathophysiology
• “Making nephrology sexy one episode at a time”

Legal disclaimer (Judy):

This podcast is for educational purposes only. The views and statements expressed on this podcast are solely those of the hosts.  This podcast should not be used as medical advice or for treatment purposes

Getting to know your hosts- 

This is the part of the podcast where for  our audience to get to know us better we  start off with a fun non medical question for our hosts. This episodes question is: 

What is one of the silliest or dumbest things you have done as a medical student or resident? or fellow? or attending?

Sophie: foley story

Judy: Morphine story

Sarah: I have so many...where to begin. As a  resident… Dr CArt story

Podcast episode 2

Case:

Your buddy Tyson a geriatrician asks you to see his patient who was just admitted to the hospital. She is a lovely 90 yo woman who still lives independently but Tyson noticed that she was not quite as sharp as she had been and checked routine labs. Her routine labs revealed a serum Na of 125, creatinine of 0.4mg/dL

Her Usom is 100 mosm/kg

Her Una is 25meq/L

He mentions that he has been trying to get her into an assisted living facility because she has been declining at home and lost a lot of weight. Her current weight is 45kg. Her family reports they drop off food for her, but they notice she does not eat it. She says she drinks ice tea and cereal most days.

Judy or Sophie: How would you approach this case

Sophie: 

This patient’s serum sodium is low at 125 meq/L with a low urine osm of 100 mosm/kg. In a hyponatremic person, who clearly doesn’t have SIADH. We know she doesn't have high ADH because her uOSM is LOW at 100mosm/kg, we need to consider other factors that impact how much water a person can drink in order to cause hyponatremia.

1. Her GFR (kidney function)
2. her solute intake 

So, to confirm, you’re saying there is no ADH around contributing to the hyponatremia? 

Sophie: Correct

Judy, do you think her kidney function is impairing her ability to excrete sufficient water?

Her kidney function is normal, so no, her water excretion should be close to 20% of her GFR, which if we remember from our last case is A LOT OF WATER.

Sarah: you mentioned the importance of knowing what her solute intake is..Sophie, what is solute intake? why is that important to you?

Sophie: Solute intake is simply a reflection of our dietary intake, most notably sodium, potassium and protein.  Protein is of course metabolized and excreted mainly as urea.

Sarah: How much solute do people  make in a day  Sophie?

Sophie: We assume that most healthy individuals consume approximately 10 mosm/kg/day. In steady state, the motto is “what goes in, must come out”, therefore we must excrete in our urine our daily solute intake, which is 10mosm/kg/day.

Sarah: how does solute intake affect how much water a person can drink?

Judy: As Sophie said, “what goes in, must come out”, which holds true for water intake and excretion as well. However, water excretion in the urine is directly dependent on having   solute present to accompany the water in the urine.

More solute means you can drink more

Sarah: So what your saying  a person  can drink more water if they consume more solute. Is there a way we can estimate the amount of solute a patient has to excrete?

Judy: Yes. For example, a 70 kg man consumes 10mosm/kg/day, which equals 700 mosm/day. Remember this means he also needs to pee out 700mosm/day of solute.

Sarah: How much volume of urine will that 700 mosm come out in?

Sophie: It depends on his urine osm. We like to use this equation:

 osm intake/measured urine osm = the volume of water needed to accompany the solute in the urine

So, if we divide his intake of 700mosm/day by his measured uosm of  100 mosm/kg, we know he can consume upwards of  7 liters/day before becoming hyponatremic.

Sarah: Judy what if his Usom was 700

Judy: osm 700/700= 1 Liter

Sarah: Sophie- how many osm does this woman in our case excrete in a day?

Sophie: Ok, let’s start with assuming that she is still consuming the average dietary intake 10mosm/kg/day of solute. At 45kg, which I might highlight is tiny (the equivalent of 99lbs), her solute intake is 450mosm a day. To calculate the urine volume, I would use the same calculation and divide her solute intake, 450mosm, by her Uosm, 100 mosm/kg, we find out she will excrete 450mosm in 4.5Liters of urine.

so, if she drinks more than 4.5 liters of water her serum sodium will decrease.

Sarah: okay so wow she can only drink 4.5liters of water before she becomes hyponatremic...that is really low.  Judy, what else could be limiting how much she can drink?

Judy: One thing that can affect how much she can drink is her small size. 

If she’s also malnourished where they consume an even lower protein load, the volume of water needed to excrete that solute load is EVEN lower. It is very possible she consumes only 8mosm/kg of solute a day, in which case 8 X 45 = 360mosm and if you divide that by her usom she would become hyponatremic if she drinks more than 3.6L

Sarah:  Okay so she can only drink 3.6L a day because she is eating very little protein and weighs very little and so the solute she has to excrete in a given day limits how much she can drink.

Does anyone want to comment on her Una-?

Sophie:  her urine Na is 25. Since it’s not incredibly low (<10mosm) she is likely not volume depleted. It is also not very high, which suggests she may have limited nutritional intake.

Sarah: okay so in this case  this patient could drink 4 liters of ice tea and become hyponatremic to 125 because she is not eating much  and does not weigh much is that correct?

Judy: yes

How would you recommend the patient be treated

Judy: restrict fluid intake to < 3 liters

Sophie: increase solute intake, especially protein

This diagnosis is sometimes referred to as “beer potomania” when it is in the case of an alcoholic drinking beer but not eating and in elderly patient eating very little it is  referred to as “tea & toast” hyponatremia

Last episode we discussed a case of hyponatremia with dilute urine which was explained by massive water intake. This episode we discuss another cause of hyponatremia with a dilute urine but in this case the hyponatremia develops with much smaller fluid consumption due to her small size and poor protein  intake

To review our learning objectives:

Normal healthy patients consume 10mosm/kg/day, which necessitates they excrete 10mosm/kg/day.

Urine volume depends on urine solute excretion and urine osmolality

Simply being smaller decreases your maximum water consumption

Elderly or in-firmed patients may consume, thus excrete fewer osm/kg

That ends episode TWO of Kidney Essentials. Thanks for tuning in! Stay safe and remember 

ALL PHYSICIANS MAKE MISTAKES SO BE KIND WITH YOURSELF HAVE SOME SELF COMPASSION AND LEARN TO LAUGH ABOUT IT...ALTHOUGH SOMETIMES THAT TAKES TIME

Sophie says goodbye

Judy says goodbye

Credits:

Seamus Klingsporn for editing

Josh strong for graphics

And of course the University of Colorado division of RENAL disease and HTN  for giving us our jobs!