• Virtual Rounds Session 13: Hyponatremia (Premed Shadowing)

Virtual Rounds Session 13: Hyponatremia (Premed Shadowing)

Throughout each premed virtual shadowing session, you will actively participate by answering and asking questions about the week’s proposed case. Like an in-person shadowing experience, we strive to stimulate students intellectually and ultimately reaffirm their interest in medicine.


Introduction – Hyponatremia

Hyponatremia is a disease process in which a person has low concentration in the blood. There are multiple etiologies of hyponatremia, and patients can present with low, normal, or high-volume status. Depending on the patient’s sodium levels, they will have no, mild, or severe symptoms. 

Case Highlights 

Mr. F is a 60 yo M with PMH of heart failure and hypertension (high blood pressure) who is presenting to the ED with generalized weakness, shortness of breath, and bilateral leg swelling.  He denies having any other symptoms.

He says that he has been taking his medicines daily, including his normal dose of a diuretic for his heart failure. He did stay that he was visiting New Orleans for his son’s wedding and has been drinking much more water than usual due to the heat, and felt more “swollen” than usual.


What is hyponatremia? Hyponatremia is a low sodium concentration in the blood. It is defined as a concentration less than 135 mEq/L. The patient’s sodium concentration tends to correlate to their symptoms. 

What are the different types of hyponatremia?

  • Hypovolemic hyponatremia (low fluid status, low sodium concentration)
    • Renal causes: thiazide diuretic use, chronic kidney disease
    • Extra-renal: GI loss, pancreatitis, burns 
  • Euvolemic hyponatremia (normal fluid status, low sodium concentration)
    • Hypothyroidism, medication (NSAIDs, sulfonylureas), glucocorticoid deficiency, Syndrome of Inappropriate antidiuretic hormone secretion (SIADH), often associated with small cell lung cancer
  • Hypervolemic hyponatremia (high fluid status, low sodium concentration)
    • Renal failure, cirrhosis, heart failure, nephrotic syndrome

When do people begin to have symptoms?Most people tend to have symptoms with sodium levels under 130 mEq/L. Our patient in the vignette, Mr. F, had a sodium level of 122.

Source: Journal of Geriatric Mental Health

How can one diagnose the type of hyponatremia?

  • Hyponatremia must first be diagnosed through looking at a patient’s sodium level. This is often done with a basic metabolic panel (BMP), a comprehensive metabolic panel (CMP), or a Chem 7. 
  • Upon seeing that someone has a low sodium level, it is important to obtain labs including: serum osmolarity, urine osmolarity, and urine sodium
  • The flow chart below shows the way in which hyponatremia is diagnosed 
Source: WikEM
  • The etiology of the hyponatremia will determine best way to treat the hyponatremia

How quickly should one’s sodium be corrected?

  • It is recommended to correct a patient’s sodium slowly, unless they are seizing or on the verge of death, with a correction that does not exceed 8-10 mEq/L/24 hours
  • For example, if someone had a sodium of 125, the goal would be to slowly correct it to 133-135 over the course of 24 hours
  • However, if someone is having seizures or on the verge of death from hyponatremia, it is okay to correct 1mEq/L/hr, until they stop having neurological symptoms (the seizures stop or they begin to seem more awake)
  • We are careful to correct slowly to prevent central pontine myelinolysis, which happens when the sodium levels in the blood go up so quickly that all the water in the myelin cells leave the cells to go to the bloodstream, thereby causing a myelin in the pons to dry up and die. 
  •  This can lead to respiratory failure and death in patients 

Take home points

    1. Hyponatremia occurs when there is a low concentration of sodium in the blood 
    2. This can be caused by a variety of medical etiologies, and it is important to determine the patient’s volume status to correctly diagnose and treat hyponatremia
    3. To properly diagnose hyponatremia, you will need a serum sodium level, serum osmolarity, urine osmolarity, and urine sodium levels
    4. There are many ways to treat hyponatremia, but it is dependent on the cause of the hyponatremia.
    5. It is generally recommended to correct the sodium at a rate of 8-10 mEq/L/ 24 hours to avoid central pontine myelinolysis, or death of the insulation cells around the pons, as this can cause death

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