Thread by @JoshMedPeds

1/ Clinical Question: A person with chronic liver disease and alcohol misuse disorder is admitted to the hospital and is found to be hyponatremic. How can we formulate a differential and sort through various probable diagnoses? Also, what the heck is even beer potomania!?

2/ Background: Getting ready for my Peds and Medicine AIs, and for me, hyponatremia is this vague, nebulous concept creating a clinical syndrome of fatigue, muscle cramping, nausea, vomiting, headaches, and disorientation.

3/ Background: Hyponatremia is a diagnosis made with repeated Na measurements of <135 mEq/L. Because sodium is our primary plasma osmole, hyponatremia is usually associated with HYPOosmolality

Source: The Fluid, Electrolyte & Acid-Base Companion (1999) @kidney_boy

4/ Tangent - Beer Potomania: anyone taking in volumes of beer can become hyponatremic excreting despite maximally dilute urine. Beer’s low protein content AND protein-sparing effect of its metabolism result in ⬇️ BUN concentrations and urinary urea excretion.

PMID: 29507848

5/ Tangent: with low solute intake, there is a minimum on how dilute urine can get, ~50 mOsm/L, and depending on solute intake, there is a maximum amount of urine they can generate. If a beer drinker's consumption exceeds this, everything above that is retained!

6/ Tangent - Beer Potomania Pathophysiology: one case of a person who ate little and drank about one 12 pack per day ingested about ~200-300 mOs; with fully functioning kidneys, this person was limited to a MAXIMUM of 4-6L of dilute urine. (a 12 pack is 4.25L!)

PMID: 26176571

7/ Tangent - Beer Potomania Pathophysiology: any intake over this will cause dilutional hyponatremia. When we add back in solutes (like IV fluids) large diuresis ensues rapidly increasing serum sodium - monitor carefully!

PMID: 26176571

/EndTangent

8/ Evaluation: Credit to Robiewon on YouTube for a rapid three step approach to hyponatremia (after a Na recheck!):

1. Edema present: think heart, liver, and kidneys
2. No edema: think SIADH or hypovolemia
3. Urine sodium #1 test - >40 mEq/L SIADH, <20 hypovolemia <20 mEq/L

9/ Evaluation & Differential: if that approach doesn’t get the job done, luckily @kidney_boy and @doc_faubel doc_faubel saved me the effort. Also, their book is 10/10!

10/ Summary:

Hyponatremia on labs?
➡️look for edema - if present, think heart, lungs or kidneys
➡️no edema, think SIADH or hypovolemia (diuresis, vomiting, diarrhea)
➡️Urine Na: <20 mEq/L - hypovolemia
➡️Urine Na: >40 mEq/L - SIADH

11/ #MedStudentTwitter Reflection: Beer potomania has some enlightening physiology, great thing to know! It feels like a good history and assessment of volume status will get me most of the way there on identifying the underlying etiology of hyponatremia. Knowledge!!

12/ Bonus Pearl: Looking at the urine specific gravity, I can use the 30x heuristic and 10-10 sign to help figure out the osmolarity. Take the last two digits of the specific gravity, and multiply it by 30 to estimate the osmolarity - and 1.010 is *roughly* isosmotic.

12/ Bonus Pearl Part II: A more detailed correspondence courtesy of The Fluid, Electrolyte & Acid-Base Companion (1999)