Hyponatremia and Hypernatremia Flashcards
What are the steps of differentiating the causes of hyponatremia?
- Diagnostic clues
- Clinical assessment of volume status
- If euvolemic, check urine Na and response to saline challenge
- if euvolemic, check SIADH
- explore risk factors
Hyperkalemia in the setting of hyponatremia suggests what two causes of hyponatremia?
Renal disease
adrenal insufficiency
What is the equation for osmolality?
2[Na] + gluc/18 + BUN/2.8
What is the normal range for serum osmolality?
285-295 mOsm/kg
What are the causes of hypervolemic hyponatremia? Describe the pathophysiology.
CHF
Cirrhosis
Nephrotic syndrome
Loss of protein in the serum decreases oncotic pressure, causing disbursement of fluid to ICF. Aldosterone released, causing more water to be reabsorbed than Na.
What is the differential for hypovolemic hyponatremia? (3)
- Diuretic use
- n/v/d
- Primary adrenal insufficiency
What is the normal kidney response (defined by FeNa) in hypovolemic, euvolemic, and hypervolemic pts?
Hypovolemic = Low Na concentration
Euvolemic = anywhere (volume is fine)
Hypervolemic =
Under what amount of urine Na should hypovolemic pts excrete?
Under 20 mEq/L
High urine Na in hypovolemic pts may be seen with what conditions?
- Diuretics
- Primary adrenal insufficiency
- Vomiting with metabolic alkalosis
What are the two major causes of low urine Na in euvolemic pts?
- SIADH
- Psychogenic polydipsia
Why should measuring urine Na not be done in clinically hypervolemic pts?
-Hypervolemia is usually associated with ineffective circulating volume (e.g. CHF). Thus urine Na will be low, despite hypervolemia
How is a small saline challenge diagnostically useful in cases of hyponatremia?
- If hypovolemic, ADH is triggered. When saline given, this should fall, and serum [Na] should rise
- In euvolemic pts, ADH is not volume dependent, and persists despite saline challenge. This results in retention of water, and worsening of hyponatremia.
When is the saline challenge contraindicated for differentiating hypovolemic hyponatremia vs euvolemic hyponatremia?
If serum [Na] less than 120
What are the 7 causes of euvolemic hyponatremia?
- Diuretics causing and SIADH
- Exercise associated or ecstasy use
- Hypothyroidism
- Psychogenic polydipsia
- Reset osmostat
- Secondary adrenal insufficiency
- SIADH
What is the diagnostic use of urine Na in differentiating euvolemic vs hypovolemic causes of hyponatremia?
- If low (less than 30), then probable hypovolemia
- If high, (over 30) suggests euvolemia
What are the three major causes of hypoosmotic, hyponatremia with a low urine osmolality?
- Psychogenic polydipsia
- Beer potamia
- TURP
What are the two major causes of hyponatremia with isoosmotic serum?
- Lipids increased
- Proteins increased
What are the two major causes of hyponatremia in the setting of hyperosmolar serum?
- Hyperglycemia
- Mannitol
How does cirrhosis lead to hypervolemic hyponatremia?
Hypoalbuminemia and splanchnic dilation decreased effective circulating volume, resulting in increased ADH
How do NSAIDs worsen hyponatremia?
Lower renal PGE2 levels, which normally antagonize ADH
What is the treatment for severe hypervolemic hyponatremia 2/2 cirrhosis?
Hypertonic saline with a rise in serum Na no more than 6 mEq/L
What causes the increase in free water over Na in hypervolemic hyponatremia 2/2 CHF?
ADH
What is the role of ACEIs in the treatment of hypervolemic hyponatremia 2/2 CHF?
Can help restore sodium levels to normal. ACE inhibitors improve cardiac output, decrease ADH secretion, and facilitate free water excretion. They also directly antagonize the effect of ADH on the collecting tubules.
What is the treatment for hypovolemic hyponatremia 2/2 CHF?
-Fluid restriction to less than 1000mL/day
-Diuretics
-
What is the treatment for hypovolemic hyponatremia 2/2 nephrotic syndrome?
Free water restriction
What is osmotic demyelination syndrome?
ODS is a complication of overly rapid correction of severe chronic hyponatremia (< 120 mEq/L for 2 or more days)
Rapid correction of chronic hyponatremia makes the serum hypertonic compared to the brain causing osmotic demyelination
How long after correction of hyponatremia does osmotic demyelination syndrome occur?
2-6 days
What are the s/sx of osmotic demyelination syndrome?
Spastic quadriparesis and pseudobulbar palsy Coma Ataxia Behavioral disorders Death
What is the normal range of urine osmolality?
- The normal 24-hour urine osmolality is, on average, 500-800 mOsm/kg of water.
- Random urine osmolality should average 300-900 mOsm/kg of water.
- After 12-14 hours of fluid intake restriction, the urine osmolality should exceed 850 mOsm/kg of water.
What antiepileptic drug classically causes SIADH?
Carbamazepine
What is the urine Na levels with SIADH?
Over 30 since no stimulus for Na retention
Why will isotonic saline administration worsen SIADH?
ADH stimulus will promote Na excretion without water loss
How do primary and secondary adrenal insufficiency cause hyponatremia respectively?
Primary = Loss of aldosterone
Secondary = Loss of cortisol leads to low BP, causing ADH release.
What are the non-renal causes of hypovolemic, hypernatremia? What urine finding confirms that it is a non-renal cause?
Excessive sweating
Diarrhea
Severe dehydration
UNa less than 10
What are the renal causes of hypovolemic, hypernatremia? What urine finding confirms that it is a non-renal cause?
Mannitol
Urine Na more than 20
What is the treatment for hypovolemic hypernatremia?
NS IVFs
What is the basic process that causes hypovolemic hypernatremia?
Losing Na and water, but more water
What is the basic process that causes hypervolemic hypernatremia?
Losing Na and water, but moreso Na
What are the non-renal reasons for hypervolemic hypernatremia?
- Too much IVFs
- Mineralocorticoid excess (overwhelms 11beta enzyme)
What is the treatment of hypervolemic, hypernatremia?
Diuretics
What is the basic pathophysiologic process behind isovolemic hypernatremia?
Loss of H2O
What are the causes of isovolemic hypernatremia?
Loss of ADH (DI)
What is the treatment for isovolemic hypernatremia?
D5 NS
