SM 202a - Hyponatremia Flashcards
What are the three major categories of hypotonic hyponatremia?
- Truly hypovolemic
- Vomiting/diarrhea
- Diuretic agents
- Cerebral salt wasting
- Edema - Low EBV but not volume depleted
- Congestive HF
- Cirrhosis
- Nephrotic syndrome
- Near euvolemic
- Addison’s disease (Adrenal insufficiency)
- Drinking too much
- Polydipsia
- Potomania
- Hyperhyroidism
- Renal failure
- SIADH
If volume and osmolality are both low, how (in general) will the body react?
The body’s #1 priority is restoring volume
- -> ADH secretion even though serum osmolality is low
- The most acute problem is hypovolemia; when volume is restored, a person with healthy kidneys and normal diet will be able to sort our the electrolytes
What are the major causes of hypotonic hyponatremia with volume depletion?
- Diarrhea + Vomiting
- Diuretics
- Cerebral salt wasting
Basically: volume depletion leads to stimulation of RAAs, which promotes Na+ reabsorption and leads to thirst and ADH release. If a patient takes in hyptonic fluids, the kidney will work to reabsorb as much fluid as possible at the cost of osmolality -> hypotnatremia
What is the appropriate treatment for hypotonic hyponatremia?
Water restriction
- If volume depletion
- Administer normal saline until euvolemic
- If edema
- Do not administer saline
- Give diuretics
- Control H2O intake
- Treat underling cause (nephrotic syndrome, CHF, cirrhosis)
- 3% saline (slowly) if neurologic symptoms of cerebral edema
- If SIADH
- Do not administer saline
- The kidney will not be able to excrete the water due to ADH secretion
What electrolyte abnormality is associated with oxytocin?
Hyponatremia
- Oxytocin acts like ADH
- Normal solute excretion + abnormal H2O retention
- -> Hyponatremia
What are the major causes of hypotonic hyponatremia due with Edema?
- Congestive HF
- Cirrhosis
- Nephrotic syndrome
Basically: Redistribution of ECF from plasma interstitium leads to perceived volume depletion. This leads to stimulation of RAAs, which promotes Na+ reabsorption and leads to thirst and ADH release. If a patient takes in hyptonic fluids, the kidney will work to reabsorb as much fluid as possible at the cost of osmolality -> hypotnatremia
When you see a low serum Na level, you know there is an excess of _____________
When you see a low serum Na level, you know there is an excess of water
What are the major causes of euvolemic hyponatremia?
- Adrenal insufficiency
- No aldosterone = cannot reabsorb Na+
- Too much fluid intake
- SIADH
- ADH secreted even when there is no physiologic reason -> H2O retention
- Hypothyroidism
What urine osmolality indicates that ADH is present?
Urine osm >100 indicates ADH is present
What is the major cause of hypotonic hyponatremia?
Increased water intake + decreased water excretion
You know the patient took in too much water, but there are several reasons for not being able to excrete it
Not caused by excess Na+ excretion
Will a patient with low effective circulating volume (ex: CHF) be more likely to develop hyponatremia or hypernatremia?
Why?
Hyponatremia
- Low effective circulating volume = stimulation of ADH
- -> Increased retention of water via ADH
- -> Increased thirst
This will replete water but not solutes
Hypovolemia is caused by a deficit of ________
Hypovolemia is caused by a deficit of Na+
Which electrolyte is a surrogate marker for tonicity?
Serum Na+
What is the equation for electrolyte-free water clearance?
Urine volume = (solute exretion / average daily urine osm)
So
CEFH2O = Urine volume * (1 - [UNa + UK] / [PNa] )
What are the signs of SIADH?
- Urine is concentrated, but serum osmolality is low
- ADH is secreted inappropriately (ex: when serum osm is low)
- -> Cannot excrete H2O load
Reset osmostat looks similar, but the patient is able to excrete the H2O load
