Term
| what is hyponatremia a disease of? |
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Definition
| water metabolism (excess) |
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Term
| what is normal serum Na+? (*test question*) |
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Definition
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Term
| what are ways that a pt can become hyponatremic? |
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Definition
| adding water, sweat, diarrhea, diuretic adm (furosemide) |
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Term
| can the body ever lose just salt? |
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Definition
| no salt loss in the body is always accompanied by water loss |
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Term
| how much salt is usually lost per L of water lost? |
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Definition
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Term
| how can diuretic adm/diarrhea use lead to hypernatremia? hyponatremic? |
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Definition
| pt has 2L H20 @ 280 mEq Na+. they lose 1 L of water and 70 mEq Na+. now they have 1 L of water and 210 mEq Na+ = hypernatremia. now if they drink 1L of fluid w/out Na+, they will become hyponatremic @ 210 Na+ for 2 L (105 mEq/L) |
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Term
| what pts have hypernatremia and hypervolemia? (*test question*) |
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Definition
| pts w/kidney failure (nephrotic syndrome, on dialysis), *pregnant women* (retain salt and water), liver failure (cirrhosis), and CHF - all marked by edema |
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Term
| how is water reclaimed from excretion by the kidneys? |
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Definition
| ADH from the posterior pituitary |
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Term
| what is ADH excretion stimlated by? |
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Definition
| hypovolemia or hyperatremia |
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Term
| what is the hallmark of ADH? |
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Definition
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Term
| what will happen in the absence of ADH? (*test question*) |
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Definition
| no water reabsorption, giving the max dilution of urine: 50-100 mOsm/kg |
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Term
| what is urine concentration under max ADH secretion? (*test question*) |
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Definition
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Term
| what is normal urine concentration? (*test question*) |
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Definition
| 280-300 mOsm/kg, also known as isosthenuria - urine concentration is the same as plasma (300 mOsm/kg) |
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Term
| is there a maximum to which ADH will respond to osmotic stimuli? (*test question*) |
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Definition
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Term
| is there a maximum to which ADH will respond to hypovolemic stimuli? (*test question*) when is this problematic? |
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Definition
| no - survival depends on BP, so therefore maintenance of volume is more important than normal serum Na+. this becomes problematic when hypovolemia is due to CHF rather than actual hypovolemia, and this results in increased TBS, edema, etc |
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Term
| a serum level of Na+ doesn't mean anything until you do a hx, review of rx, phys exam b/c you could have a wonky hyponatremic level for what 3 different reasons? |
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Definition
| addition of H2O, loss of Na+, and increase of TBS (total body sodium) |
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Term
| what are important questions to ask in the hx? |
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Definition
| is the pt on diuretics, dialysis, have they had diarrhea, etc. |
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Term
| how will a hypovolemic hyponatremic pt present clinically? |
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Definition
| dehydrated, hypotensive, tachycardic, dry mucous membranes, orthostatic hypotension |
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Term
| how will a hypervolemic hyponatremic pt present clinically? |
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Definition
| edema (hallmark), w/cirrhosis - ascites |
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Term
| what is euvolemic hyponatremia? who has this? what causes it? |
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Definition
| water volume has a normal appearance - but Na+ levels are low. usually these pts have lung/brain CA - this is a state of water intoxication, but no edema is associated. generally this is caused by ADH continuing to be secreted for some inappropriate reason (lung cancer, pneumonia, something bad in brain, infection, tumor, etc.) - called syndrome of inappropriate ADH (SIADH) |
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Term
| what is the hallmark of euvolemic hypoatremia? (*test question*) |
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Definition
| concentrated urine despite the absence of any osmotic/volume stimulus for ADH |
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Term
| what are lab tests to order when suspecting hypo/hypernatremia? |
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Definition
| urine osmolality and urine specific gravity (water has no particles and a specific gravity of 1 - the more particles a solution has, the higher the specific gravity) |
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Term
| if a pt is hypovolemic: diaphoretic (indication of CO), tachycardic, thirsty - what would the expected urine osmolality be? |
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Definition
| 1200 mOsm/kg - max concentration, trying to retain water |
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Term
| what would the expected urine osmolality for a CHF pt (not on diuretics)? |
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Definition
| urine osmolality would be high (1200 mOsm/kg), b/c the kidneys will be absorbing Na+ and water |
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Term
| why would a pt with lung cancer be secreting ADH inappropriately? how would this affect the urine osmolality? |
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Definition
| some lung tumors will secrete ADH, and medications such as tegretol can also do this. urine osmolality could be anything from 200-1200, depending on the level of ADH |
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Term
| how are pts w/decreased TBS (total body Na+) treated? (*test question*) |
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Definition
| saline, but it is important to *never replace Na+ faster than .5mEq/L per hour (12 mEq/L/day)* or you risk central pontine myelinolysis (neurologic disease) |
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Term
| how are pts with increased TBS treated? |
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Definition
| furosemide, salt/water restriction |
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Term
| how are pts with euvolemic hyponatremia treated? |
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Definition
| water restriction - sometimes med such as demeclocycline are used to block ADH |
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Term
| where is the bulk of K+ in the body? |
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Definition
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Term
| what is a common K+ related problem w/diabetics? |
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Definition
| inability to take up K+ intracellularly - causes hyperkalemia |
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Term
| how can hyperkalemia result from hemolytic rxns (tranfusion), crush injury, rhabomyelyses? |
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Definition
| a lot of K+ is released into the system at once and cannot be reabsorbed at once |
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Term
| what is the most common cause of hyper/hypokalemia excluding pts w/DM? |
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Definition
| disorders of K+ secretion due to renal tube defects (inability to either reclaim or secrete K+ or secrete too much K+) |
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Term
| where is most K+ reabsorbed? secreted? |
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Definition
| reabsorbed in the PCT, secreted in the DCT |
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Term
| what is the effect of aldosterone? |
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Definition
| cells in the DCT express more Na+ pumps - allowing them to reabsorb more Na+ |
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Term
| what if the effect of increased Na+ reabsorption? |
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Definition
| the increased + influx into the cell leaves a - charge in the tubule, which pulls K+ out into the tubule from the cell (so, the more Na+ movement you have, the more K+ movement into the tubule you have) |
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Term
| what is the effect of hyperaldoesteronism (tumor, pills, etc) on a pt? |
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Definition
| hypokalemia, increased Na+ reabsorption/increased K+ excretion |
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Term
| how does increased Na+ reabsorption affect H+ secretion and HCO3- levels? |
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Definition
| H+ is also secreted into the tubule against its concentration gradient BUT with electric gradient created by Na+ reabsorption. this movement of H+ into the tubule also allows HCO3- to be reabsorbed - b/c HCO3- is created intracellularly with the freeing of H+ (from carbonic acid) to be secreted. |
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Term
| anything that increases Na+ reabsorption (like aldosterone) ________ K+ and H+ secretion |
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Definition
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Term
| what is the hallmark of aldosterone excess? (*test question*) |
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Definition
| hypokalemic metabolic alkalosis - b/c increased Na+ reabsorption means increased K+ and H+ secretion (hypokalemic) and increased H+ secretion means increased HCO3 reabsorption (alkalosis) |
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Term
| what is the hallmark of an aldosterone deficit? what can cause this? |
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Definition
| hyperkalemic metabolic acidosis - (see explanation for implications of aldosterone excess and reverse it). this can be caused by aldoesterone deficiency, resistance, or drugs such as Na+ channel blockers such as amiloride (weak diuretic that blocks Na+ channel distally) |
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Term
| can furosemide cause aldosterone excess? |
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Definition
| yes, due to volume depletion and the body's compensatory response w/aldosterone - resulting in hypokalemic metabolic alkalosis |
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