Background:

64-year-old with an upper respiratory tract infection is evaluated in the clinic. He has a history of high blood pressure. His intake has been poor the last few days. Current medications include amlodipine, irbesartan, and hydrochlorothiazide. He has no focal neurologic signs. The blood pressure is 111/67. There is no swelling. He appears euvolemic, and the serum sodium is noted to be 121. The bun is 8, potassium 3.1. Urine osmolality and other appropriate studies are pending.

Please answer the following questions:

What is the most likely diagnosis?

Euvolemic (isovolemic), chronic, hypotonic hyponatremia.

Patient follow up: the serum osmolality (osm) came back at 242. The urine osm was 480.

Assume that this is the correct diagnosis as you work through the following questions and review the discussion below.

What is the next step?
* Admit for iv fluid (either hypertonic saline or normal saline based on lab results)
* Stop the hydrochlorothiazide and fluid restrict. Admit.
* Order tolvaptan
* Give him some salt tablets

Stop the hydrochlorothiazide and fluid restrict. Admit.

This is an appropriate starting management strategy.

Chronic hyponatremia is defined as a drop in serum sodium in less than 48 hours.
A
True
B
False

False

This is acute hyponatremia.

Rapidly increasing serum sodium levels in patients with chronic hyponatremia can lead to osmotic demyelination syndrome (ODS).
A
True
B
False

True

See the discussion below for a picture, brain MRI, of what osmotic demyelination looks like.

Hypertonic saline, 3%, is an appropriate management strategy for symptomatic and acute isovolemic hypotonic hyponatremia?
A
True
B
False

True

Is administering 0.9% saline an effective treatment for isovolemic hypotonic hyponatremia in the patient described above?
A
True
B
False

False

Providing intravenous normal saline can treat hypovolemic hypotonic hyponatremia but does not benefit a patient with isovolemic hypotonic hyponatremia.

Discussion:

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Euvolemic Chronic Hyponatremia – Management

Fluid Restriction and Withholding Hydrochlorothiazide

For asymptomatic and chronic isovolemic hypotonic hyponatremia, the most appropriate management is fluid restriction and withholding hydrochlorothiazide. This patient likely has chronic hyponatremia because of hydrochlorothiazide use, which impairs urine-diluting capacity.

Definition: considered chronic hyponatremia if no observed drop in serum sodium in less than 48 hours.
Approach: slowly increase serum sodium by 4.0 to 6.0 mEq/L in a 24-hour period, not exceeding 8.0 mEq/L to avoid rapid increase and risk of osmotic demyelination syndrome (ODS).
Avoid osmotic demyelination syndrome: high-risk factors for ODS include older age, female sex, hypokalemia, and serum sodium level <120 mEq/L. Our patient is younger, male, the serum sodium is greater than 120. He has hypokalemia. The potassium should be replaced.

Other Management Strategies (Important To Know)

Normal Saline

Effective for hypovolemic hypotonic hyponatremia but not suitable for isovolemic hyponatremia in this patient. Administering 0.9% saline could worsen hyponatremia by dilution compared to the patient’s urine concentration. Our patient had a urine osm of 480. The measured osmolality of normal saline is 286. That said, hydrochlorothiazide is a diuretic. Our patient’s blood pressure was on the lower side. His intake was poor. There may be a component of dehydration here. So normal saline might help based on trending the values and the patient’s clinical status over time.

Hypertonic Saline

3% hypertonic saline can be appropriate for symptomatic and acute isovolemic hypotonic hyponatremia, but it is not indicated in this patient. The patient is asymptomatic. The hyponatremia is chronic. If 3% saline is going to be used, a 100-mL bolus of 3% saline can be given to increase serum sodium by 2.0 to 3.0 mEq/L, with careful monitoring to prevent overcorrection and decrease the likelihood of osmotic demyelination syndrome.

Tolvaptan

Tolvaptan is a V2 receptor antagonist that can increase free water excretion by blocking V2-receptor aquaporin 4 insertion. This approach may lower urine concentration and correct serum sodium but poses a risk of osmotic dymyelination syndrome because of potential rapid over correction of the serum sodium.