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In hyponatremia, what lab tests will you send as part of the initial evaluation, and explain the pathway and resulting diagnosis
- Plasma Osmolality
- If normal (275-295 mosm/kg H2O), etiology is Pseudohyponatremia, Hyperglycemia, Isosmotic irrigating solution
- If decreased (<275 mosm/kg H2O), send for Urine osmolality
- If Urine osm is appropriately low (<100 mosm/kg H2O), etiology is Primary Polydipsia
In a post-neurosurgical pt, how do you differentiate between hyponatremia from SIADH vs. Cerebral salt wasting?
- Both are very similar with high urine osmolality compared to serum osm, but SIADH pts have normal EABV (effective arterial blood volume), have low uric acid, and normtensive.
- On the other hand, a pt with cerebral salt wasting will have low EABV and hypotension.
- Both are treated differently. SIADH is treated with fluid restriction, while cerebral salt wasting is treated with NS infusion
What are the manifestations of hyponatremia?
nausea, malaise, headache, lethargy, muscle cramps, restlessness, disorientation, and obtundation.
In the treatment of hyponatremia, how fast would you raise the serum Na level?
In the treatment of chronic hyponatremia, limiting serum sodium correction to less than 10 to 12 meq/L (10 to 12 mmol/L) within 24 hours and less than 18 meq/L (18 mmol/L) within 48 hours helps to prevent osmotic demyelination.
What intervention would you do if the serum Na in hyponatremia is corrected too rapidly?
infuse hypotonic fluid, or start demeclcycline
What medications are useful for hyponatremia? When are they contraindicated?
Conivaptan and tolvaptan are approved to treat euvolemic and hypervolemic hyponatremia, but vaptan agents should not be used to treat hypovolemic hyponatremia.
In a pt with polyuria, what urine osmolality is suggestive of osmotic diuresis?
A urine osmolality greater than 300 mosm/kg H2O (300 mmol/kg H2O) in a patient with polyuria is suggestive of osmotic diuresis.