Hyponatremia Flashcards
(30 cards)
What is hyponatremia?
Serum sodium concentration of <135 mmol/L.
It is a disorder of water balance reflected by an excess of total body water relative to electrolytes (total body sodium and potassium) leading to low plasma osmolality (i.e., <275 mmol/kg).
Briefly describe what causes hyponatremia
Hyponatraemia is generally caused by an increase in renal water reabsorption due to release of vasopressin (arginine vasopressin also known as antidiuretic hormone) along with water intake, and can occur in situations of volume depletion, volume overload, or normal volume.
What are the 3 different types of hyponatremia?
- Hypovolaemia
- Euovolemia
- Hypervolaemia
Briefly describe hypovolaemic hyponatremia
Loss of intravascular volume.
Causes:
- Gastrointestinal fluid loss (e.g. severe diarrhoea or vomiting)
- Third spacing of fluids (e.g. pancreatitis, severe hypoalbuminaemia)
- Addison’s Disease
- Salt-wasting nephropathy
- Cerebral salt-wasting syndrome (a rare cause of hyponatraemia resulting from urinary salt wasting)
- Mineralocorticoid deficiency
Briefly describe euvolaemic hyponatremia
Normal volume status.
Causes:
- Medications (e.g. vasopressin, diuretics, antidepressants, opioids)
- SIADH
- High fluid intake: can result from intense/prolonged physical activity or surgery
- Hypothyroidism
Briefly describe hypervolaemic hyponatremia and what causes this
Loss of effective intravascular volume.
Causes:
- Acute kidney injury/chronic kidney disease
- Congestive heart failure
- Cirrhosis
- Nephrotic syndrome
What is the most common form of hyponatremia?
Hypotonic (hypo-osmolar) hyponatraemia.
What are the risk factors of hyponatremia?
- Older age
- Hospitalisation
- SSRI use
- Thiazide diuretic use
- Underlying medical conditions
- Congestive heart failure
- Cirrhosis
- Nephrotic syndrome
- Acute kidney injury
- Chronic kidney disease
What are the signs of hyponatremia?
- Signs of cerebral oedema→ altered mental status, seizures and coma
- Orthostatic hypotension
- Abnormal JVP
- Poor skin turgor
- Dry mucous membranes
- Absence of axillary sweat
- Oedema
- Rales or crackles on lung ausculation
What are the symptoms of hyponatremia?
- High fluid intake
- Fluid losses
- Low urine output
- Weight changes
- Mild cognitive symptoms→ include confusion, headache and balance difficulties
Why can hyponatremia lead to seizures?
Osmolality inside the brain cells remains higher than the serum and water enters the brain cells causing cerebral oedema. This leads to symptoms including nausea, vomiting, altered mental status, and eventually seizures and/or brain herniation and death.
What investigations should be ordered for hyponatremia?
- Serum sodium concentration
- Serum electrolytes, urea, creatinine and glucose
- Serum osmolality
- Urine sodium concentration
Why investigate serum sodium concentration?
Should be ordered in all patients with suspected hyponatraemia.
A serum sodium concentration <135 mmol/L (corrected for hyperglycaemia) confirms the presence of hyponatraemia.
Why investigate serum electrolytes, urea, creatinine and glucose?
Should be ordered in all patients with suspected hyponatraemia. May reveal other electrolyte abnormalities or renal impairment.
May show mixed electrolyte abnormalities.
Why investigate serum osmolality?
Serum osmolality can be used to differentiate between hypotonic and hypertonic hyponatraemia.
Variable:
- Serum osmolality <275 mmol/kg: indicates hypotonic hyponatraemia
- Serum osmolality >295 mmol/kg: indicates hypertonic hyponatraemia
- Serum osmolality normal: indicates isotonic hyponatraemia (pseudohyponatraemia)
Why investigate urine sodium concentration?
Ordered to confirm the presence of hypovolaemia or euvolaemia. A spot urine test allows urinary sodium concentration to be measured quickly and conveniently
Briefly describe the treatment principles of treating hyponatremia
The management of hyponatraemia depends primarily on whether the onset is acute (i.e., <48 hours) or chronic (≥48 hours).
This is because acute onset indicates the likelihood of cerebral oedema, which requires prompt treatment in a hospital. Chronic hyponatraemia should be managed more conservatively to avoid the consequences of rapid correction (e.g., myelinolysis); specific treatment depends on the volume status of the patient.
Briefly describe the treatment of acute onset (<48 hours) or symptomatic hyponatremia
- Hypertonic (3%) saline infusion
- Supportive care (e.g. establishing intravenous access, giving supplemental oxygen, seizure control, intubation) should be initiated depending on the presentation
- Treat underlying cause
Briefly describe the treatment for hypovolaemic hyponatremia
- Isotonic intravenous fluids (e.g. normal saline 0.9% or a balanced solution such as lactated Ringer’s solution)
- Treat underlying cause
Briefly describe the treatment for hypervolemic hyponatremia
- Fluid restriction
- Treat underlying cause
- A diuretic can be added if hypervolaemia is present and the underlying condition warrants it
- If fluid restriction fails, a ADH receptor antagonist should be considered
Briefly describe the treatment for euvolemic hyponatremia
- Fluid restriction
- Treat underlying cause
- If fluid restriction fails, a ADH receptor antagonist should be considered (e.g. tolvaptan, deomeclocycline)
What are the complications of hyponatremia?
- Cerebral oedema
- Myelinolysis
- Osteoporosis
How should over correction of serum sodium (via treatment) be treated?
All active treatment should be stopped and treatment with free water intake and/or desmopressin should be initiated.
Cerebral oedema and myelinolysis can occur due to rapid sodium correction. How can this be prevented?
Slow rate of serum sodium correction (i.e., <8 mmol/L/day).
