before I go on with tonight's stuff let me get out of the way a brief caveat on how to handle hyponatremia! electrolyte/acid/base imbalances in the human body is a biggie and you need to know proper algorithm on how to handle a pt in such states.
someone comes in with hyponatremia measure their serum osmolality see if it high, low or normal
if it is high, the problem is glucose remember for every hundred over glucose is you lose 1.6 sodium
if it is normal, the problem is lipids or proteins
if it is low you must figure out their volume status
how do you check out for volume status? you'll check out their state, if they have edema it is high, check for orthostatic hypotension tachycardia to see if high it is an edematous condition like heart failure, liver failure or nephrotic syndrome ..
if the extracellular fluid volume is low, they are fluid depleted then you must measure urine sodium
if the urine sodium is low i.e <10 then they are probably losing fluid from the skin or the GI tract..
if the urine sodium is high >20 they are probably losing fluid from their kidneys
if the extracellular fluid volume is normal, it is almost always SIADH or one of the drugs causing SIADH, could be water intoxication, could be a thyroid problem