Hyponatremia Flashcards
Q: What is hyponatremia?
A: Hyponatremia is a common electrolyte disturbance where the serum sodium concentration is less than 135 milliequivalents per liter.
Q: What are the mechanisms that can contribute to hyponatremia?
A: Increased serum levels of ADH, increased renal sensitivity to ADH, excessive free water intake, and low solute intake.
Q: How can hyponatremia be categorized based on the underlying cause?
A: Hyponatremia can be categorized as hypovolemic, euvolemic, and hypervolemic.
Q: What should be the first step if a patient presents with hyponatremia?
A: Perform an ABCDE assessment to determine if they are unstable or stable.
Q: What actions should be taken for an unstable patient with hyponatremia?
A: Stabilize the airway, breathing, and circulation; obtain IV access, consider giving IV fluids, consider central venous access, and provide continuous vital sign monitoring.
Q: What sodium level is often seen in unstable individuals with hyponatremia, and what can it result in?
A: A sodium level below 125 milliequivalents per liter, which can result in cerebral edema and severe clinical manifestations like seizures or respiratory arrest.
Q: What should be done for a stable patient with hyponatremia?
A: Obtain a focused history and physical examination, order a basic metabolic panel (BMP), and assess for true hyponatremia by ordering a plasma osmolality.
Q: What does a plasma osmolality greater than 280 milliosmoles per kilogram indicate?
A: It could indicate normal (280-295) or hypertonic (>295). If between 280 and 295, consider pseudohyponatremia; if above 295, consider hyperosmolality.
Q: How is pseudohyponatremia diagnosed?
A: By elevated serum triglycerides and serum protein levels.
Q: What indicates hyperosmolality in hyponatremia?
A: Plasma osmolality above 295 milliosmoles per kilogram, commonly due to glucose or mannitol.
Q: How does hyperglycemia affect serum sodium concentration?
A: For every 100 mg/dL increase in serum glucose, serum sodium falls by about 1.6 milliequivalents per liter.
Q: What should be assessed if plasma osmolality is below 280 milliosmoles per kilogram?
A: The patient’s volume status to determine the underlying cause.
Q: What are the signs of hypovolemic hyponatremia?
A: Elevated heart rate, orthostatic drop in blood pressure, sunken eyes, dry mucous membranes, and decreased skin turgor.
Q: What should be ordered for hypovolemic hyponatremia?
A: A urine sodium level.
Q: What do urine sodium levels below 20 millimoles per liter in hypovolemic hyponatremia suggest?
A: Extrarenal causes such as gastrointestinal losses, insensible losses, or third spacing.
Q: What do urine sodium levels above 20 millimoles per liter in hypovolemic hyponatremia suggest?
A: Renal causes such as diuretic use, mineralocorticoid deficiency, bicarbonaturia, cerebral salt wasting, or obstructive uropathy.
Q: What are the signs of euvolemic hyponatremia?
A: Normal heart rate, no orthostatic drop in blood pressure, moist mucous membranes, normal skin turgor, and no signs of hypervolemia.
Q: What tests should be ordered for euvolemic hyponatremia with urine sodium >20 mmol/L and urine osmolality >100?
A: TSH, free T4, and morning cortisol or an ACTH stimulation test.
Q: What does elevated TSH and low free T4 indicate in euvolemic hyponatremia?
A: Hypothyroidism.
Q: What does low morning cortisol or decreased response in ACTH stimulation test indicate in euvolemic hyponatremia?
A: Glucocorticoid deficiency.
Q: What is the diagnosis if TSH, free T4, and ACTH stimulation tests are normal in euvolemic hyponatremia?
A: Syndrome of inappropriate antidiuretic hormone secretion (SIADH).
Q: What conditions can cause hyponatremia with excessive water ingestion and increased ADH?
A: Exercise-induced hyponatremia and MDMA (ecstasy) use.
Q: What is the diagnosis if urine sodium <20 mmol/L and urine osmolality <100 in euvolemic hyponatremia?
A: Primary polydipsia or low-solute intake (tea and toast hyponatremia, beer potomania).
Q: What are the signs of hypervolemic hyponatremia?
A: Acute weight gain, orthopnea, dyspnea, increased jugular venous pressure, subcutaneous edema, or ascites.
Q: What should be ordered for hypervolemic hyponatremia?
A: A urine sodium level.
Q: What does urine sodium below 20 mmol/L in hypervolemic hyponatremia suggest?
A: Heart failure, cirrhosis, or nephrotic syndrome.
Q: What does urine sodium above 20 mmol/L with decreased GFR in hypervolemic hyponatremia suggest?
A: Renal failure (acute kidney injury or chronic kidney disease).
Q: What is the overall approach for diagnosing hyponatremia?
A: Order plasma osmolality: if >280 mOsm/kg, consider pseudohyponatremia or hyperosmolality; if <280 mOsm/kg, diagnose hyponatremia and assess volume status.
