Emergency Medicine is Hard

Classifications:

• Mild hyponatremia – Na 130-134
• Moderate hyponatremia – Na 121-129
• Severe hyponatremia – Na <120

When sodium is low in the extracellular environment, water tends to diffuse where salt is high (e.g. the intracellular environment). This causes all cells to swell, but particularly the cells in the brain which have a limited amount of space (e.g. the cranium) to expand. As a result, the worried complication of severe hyponatremia is brain herniation. With lower sodium, the risk of herniation and seizure increases.

Na 115-119: 2.5% risk of seizure 

Na 110-114: 5% risk of seizure

Na <110: 10% chance of seizure

Acute v. Chronic Hyponatremia

Acute hyponatremia occurs within 48 hours and requires aggressive therapy because there is high risk for cerebral edema and seizures

Chronic hyponatremia occurs >48 hours and requires less aggressive therapy because there is a higher risk of complications (e.g. osmotic demyelination syndrome) with aggressive therapy

Management of ACUTE hyponatremia

The goal is a 4-6 mEq/L increase in serum sodium during the first 24 hours. If the patient is symptomatic, this goal should be achieved in 6 hours or less. 

***Max rate of correction: 8 mEq/L in the first 24 hours

Here is what treatment for the first 6 hours might look like:

If they are acutely hyponatremic AND asymptomatic, you have time and 50 cc of 3% saline boluses can be given until the patient is producing urine

If they are acutely hyponatremic AND symptomatic, you need to treat more aggressively and 100-300 cc bolus of 3% saline can be given; each 100cc bolus is given over 10 minutes. *

***Trick of the trade: 1 Amp of sodium bicarbonate can be given when 3% NS has not been readily prepared by pharmacy. An ampule of sodium bicarbonate 8.4% (50 mL) contains 50 mEq of sodium, comparable to 51.3 mEq of sodium found in 100 mL of 3% sodium chloride . 

Management of CHRONIC hyponatremia

The goal is a 4-6 mEq/L increase in serum sodium during the first 24 hours. Do NOT exceed a 4-6 mEq/L/day correction so ERR closer to a 4mEq/L/day increase. In the treatments below, notice how the goal is the same, but we’re especially concerned for overcorrection.

 If they are chronically hyponatremic AND asymptomatic, you have time! Treat slowly with 15-30 cc aliquots of 3% NS every hour. If you are concerned for overcorrection, give DDAVP. 

If they are chronically hyponatremic AND symptomatic, you need to treat aggressively as above with 100-300 cc bolus of 3% saline; each 100cc bolus is given over 10 minutes.*

However, if the cause of hyponatremia is rapidly reversible (e.g. volume depletion, adrenal insufficiency, SIADH), pretreat with DDAVP due to the high risk for overcorrection and osmotic demyelination syndrome. 

Disposition:

Admit these patients to the ICU and please AVOID use of isotonic saline (e.g. normal saline) in the treatment of these patients.

In a process known as desalination, high levels of anti-diuretic hormone (ADH) will cause further excretion of sodium and can worsen hyponatremia.