“The Mountain Model of Hyponatremia” is an educational project by Joel Topf and me.
Imagine this is the clinical scenario of severe hyponatremia:
- You are driving in a car at the top of a mountain. (The top of the mountain is the low sodium level.)
- There is a forest fire behind you. (The fire represents brain swelling and seizures if the sodium level drops much lower.)
- Your goal is to drive safely to the bottom of the mountain. (The bottom of the mountain is a normal sodium level.)
- But, to be safe, you should follow the “sodium speed limit”: a rise in sodium of 8 every 24 hours. (If you exceed this “sodium speed limit,” you increase the risk of a car crash: osmotic demyelination syndrome.)
Based on this model, there are five possible therapies for patients with hyponatremia:
- Press the accelerator (when the car is in “drive”): 3% (hypertonic) saline
- Press the accelerator (but the car may be in “drive,” “neutral,” or even “reverse”): 0.9% (normal) saline
- Cruise control: desmopressin/DDAVP and 3% (hypertonic) saline (“proactive strategy”)
- Press the brake: desmopressin/DDAVP (or large amounts of D5W) (“reactive strategy”)
- Reverse gear: desmopressin/DDAVP and D5W (“rescue strategy”)
- The “sodium speed limit” might change depending on the clinical situation.
- The slope of the mountain represents rapid correction due to water diuresis that can occur in patients with a reversible cause of hyponatremia (hypovolemia, beer potomania/low solute hyponatremia, adrenal insufficiency, and other causes).
- If a patient has SIADH, the mountain might slope upward. (This is a separate figure.)
- If the patient has SIADH, giving 0.9% (normal) saline may not work or may cause the sodium to go down — when you press the accelerator, the car may be in “neutral” or even “reverse.” (See therapy #2.)
- Usually, fluid restriction is also important.
- In the right clinical circumstances, other therapies might include salt tablets, loop diuretics, urea, and vaptans. (These are not included in the model.)