1a/14

It’s 1:34 p.m. and the ED pages you for hyponatremia.

A 45 y/o M with no known medical history presents after a seizure with a sodium of 102 mEq/L.

#tweetorial #MedTwitter #Nephtwitter #hyponatremia @theskeletonkeygroup

What's your first move?

1b/14

The initial evaluation of hyponatremia must “evaluate osmolality excluding hyperglycemia and other causes of non-hypotonic (SOsm >275) hyponatremia.” - per the European Guidelines (PMID: 24569125)

We find a hyperosmolar hyponatremia:

2a/14

What is the most likely cause of hyponatremia?

2b/14

Hyperglycemia-related hyponatremia is staring us in the face.

In insulin deficiency/hyperglycemia, glucose is “effective” osmole, drawing fluidfrom the intracellularextracellular space, diluting sodium.

Glucose Up , Sodium Down

3/14

Reminder

“Effective” osm (gluc, Na, mannitol)
-create osmotic gradient, increase tonicity, cause water to shift out of cells

“Ineffective “ osm (BUN, EtOH, glycine)
-no osmotic gradient, no change in tonicity, no water shifts

4a/14

Hold on…

Glucose >4000 — greater than the laboratory limit of detection.

Did our patient set a new Guinness World Record for the highest sodium?

4b/14

A sodium >4000 is probably incompatible with life and likely a laboratory error.

Houston, we have a problem.

5/14

Osmolality, the concentration of solute per kg of water, is used to help estimate a more accurate glucose measurement.

NA 2
BUN 2.8
Glucose 18

6a/14

Can we account for all the 350 mOsm we measured?

Na 102 x 2 = 204 mOsm
BUN of 50 / 2.8 = 18 mOSm
Normal osmol gap = 10 mOsm
Glucose of =

6b/14

Measured: 350 mOsm
Calculated: 232 mOsm
The remaining 118 mOsm are due to glucose.

7a/14

POP QUIZ

What is the conversion factor from mOsm/kg to mg/dL of glucose?

7b/14

18 x 118 mOsms = 2,124 mg/dL

Not quite the Guinness World Record glucose of 2,656 mg/dl, but certainly an impressive value and much less than the laboratory reported >4000.

8a/14

To correct sodium for hypernatremia:

for every mg/dL of glucose over we add a correction factor

What correction factor do you like to use?

8b/14

Traditionally 1.6 is used.

Hiller et al proposed 2.4 (PMID: 10225241).

The nephrology fellows @NephBCM like @SaynaNorouzi use 2.0 to make it easy.

9/14

Using measured gluc >4000, Na corrects to >164

Using calculated gluc 2,124, Na corrects to 134

We’ve done the mathematical heavy lifting

10/14

This is a case of hyperglycemia-related hyponatremia in the setting of Hyperglycemic Hyperosmolar State (HHS)

hyperglycemia
hyperosmolality (>320)
AMS/seizure
absent ketones

11/14

Let’s treat the patient.

With insulin, cells consume glucose, fluid shifts back from the extracellular intracellular, correcting Na in the process.

Timing of correcting blood glucose is a rate of 50 - 75 mg/dL/hr per the ADA (PMID: 19564476)

12a/14

So why did the patient have a seizure?

12b/14

HHS may cause altered mental status, seizures, and death, but the exact pathophysiology is unclear.

Whereas rapid changes in osmolality cause cerebral edema in children , it very rarely occurs in adults .

Idunno, bro!

13/14

In this case, the patient was admitted to ICU, received intravenous fluids and insulin per HHS protocol.

Glucose Down , Sodium Up

Sodium improved to 134, exactly our estimation!

14/14

To summarize:

Glucose is “effective” osmole, drawing fluid from the intracellular to the extracellular space, diluting sodium.
Accurate measurements of serum osmolality and glucose help to predict the corrected sodium.

Check out the visual abstract and full blog post at: https://renalfellow.org/2020/05/11/skeleton-key-group-electrolyte-case-8/

Special thank you to these great people, among others!
@DTomacruzMD, @amyaimei, @SaynaNorouzi, @kkalra_22, @iheartkidneys, @NephroGuy, @RyannSohaney, @drM_sudha, @kidney_boy, @TheSkeletonKG