Thread by @aishaikh

Polyuria : The Perfect Storm

-Nephrology is consulted for Urine output of 9L in one day

-Pt. with AML, T2DM has been in the hospital for > 2 weeks for pneumonia, sepsis & subsequently developed Sweet Syndrome & was started on steroids

1/

Approach to polyuria
Step: 1
Is this water diuresis or solute diuresis?

-Check urine osmolality
Measured Urine osm. = 368 mOsm/kg
So, total daily osmole excretion = 3312 osmoles (368 X 9 L as the patient’s urine output is 9L)

This is solute diuresis
2/

Why is this solute diuresis?
Normal daily osmole excretion in an adult on a regular diet is about 750-900 mOsm/day

This patient’s urine osmolar excretion in one day was
3312 osmoles

3/

What is contributing to solute diuresis in this patient?

Let’s calculate the urine osmolality
-Urine spot Na: 129 mEq/L
-Urine spot K: 11 mEq/L
-Urine urea nitrogen: 173 mg/dL
-Urine glucose: 500 mg/dL

2x(Na + K) + UUN/2.8 + glucose/18 = 371 mOsm/kg

4/

So, the calculated and measured urine osmolality in this patient are the same
-Measured urine osmolality = 368 mOsm/kg
-Calculated urine osmolality = 371 mOsm/kg

Hence there is no ‘unmeasured’ solute contributing to the solute diuresis

5/

So, which one of these solutes is responsible for the solute diuresis in this patient?
-Na?
-Urea?
-Glucose?

6/

Based on the urine Na, urine urea nitrogen and urine glucose measurements, and the total urine output of 9L in 24 hrs., let’s calculate the urine osmolar excretion of Na, urea and glucose

7/

Based on the urine Na, urine urea nitrogen and urine glucose measurements, and the total urine output of 9L in 24 hrs., let’s calculate the urine osmolar excretion of Na, urea and glucose

7/

Urine osmolar excretion of Na, Urea and Glucose in 24 hrs was:

Na: 2322 osmoles/day
Urine Na 129 mEq/L x 9L = 1161 + an accompanying anion 1161 x 2 = 2322 osmoles/day

Urea: 558 osmoles/day
UUN 173 mg/dL / 2.8 = 62 mmol/L x 9L = 558 osmoles/day

8/

Urine osmolar excretion of glucose in 24 hrs. was:

Glucose: 252 osmoles/day
Urine glucose 500 mg/dL / 18 = 28 mmol/L x 9L = 252 osmoles/day

9/

So the contribution of each of these solute towards urine osmolar excretion in 24-hrs. was:

Salt (Na) diuresis: 2322 osmoles
Urea diuresis: 558 osmoles
Glucose diuresis: 252 osmoles

10/

This was predominantly salt diuresis but urea and glucose were also contributing to the solute diuresis

11/

Now back to the patient who has DM, was admitted w/ sepsis, pneumonia & received IVF during their hospital stay for hypotension

IVF stopped as pt. developed gen. edema

Pt. developed Sweet syndrome & was given steroids which caused hyperglycemia
12/

Then pt’s BP improved, pt. started feeling better and started eating better and was given protein shakes

Pt.‘s ursine output increased and his edema started improving
13/

Salt diuresis occurred as the pt. was excreting salt that pt. had received (IVF) during the hospital stay

Glucose induced polyuria was triggered by hyperglycemia due to steroids

Urea induced polyuria was due to increased protein intake & steroids
14/

The polyuria in this patient was solute diuresis

The important thing was to convince the primary team to not give more salt containing IVF to ‘replace’ the high urine output as that would have perpetuated the polyuria

15/

The serum Na in this patient was normal and BP was high

The serum Na did not change with polyuria as the electrolyte free water loss was low (minus 0.26L)

This case highlights the importance of distinguishing b/w water diuresis & solute diuresis

End/