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normal serum sodium
135-145 mEq/L, >90% of the osmolality of the ECF
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hypertonic hyponatremia
serum osmolality >285, excessive nonsodium effective osmoles, excess glucose, treatment: treat underlying cause
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isotonic hyponatremia
serum osmolality 280-285, more of a lab artifact and pretty much a non-issue today because of improved laboratory methods of measuring serum sodium
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hypotonic hyponatremia
serum osmolality <280, can be hyper, iso and hypovolemic
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calculate serum osmolality
P osm=2 * (Na) + glu/18 + BUN/2.8
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hyponatremia
serum sodium <135 mEq/L
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hyponatremia signs and sx
n&V, anorexia, lethargy, HA, muscle cramps
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neurologic sx of hyponatremia
restlessness, disorie, agitation, psychosis, depressed deep tendon reflexes (DTR), Cheyne-stokes respiration, seizures, coma, respiratory depresion, permanent brain damage, death
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osmolar gap
measured serum osmolality-calculated osmolality>15 indicates presence of excess hyperosmolar compounds-may be due to hyperglycemia, for every 100 mg/dl increase in blood sugar>normal, serum sodum decreases 1.7 mEq/L, admin of hyperosmolar solution (mannitol, glycerin), toxicity/poisoning (ethanol, methanol, ethylene glycol)
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hypovolemic hyponatremia
posm<280, loss of sodium and water but sodium >>water loss
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signs of being hemodynamically unstable
postural hypotension, HR > or equal 100bpm, SBP <100 mmHg
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renal sodium losses
>20mEq/L(most common cause) thiazide diuretics(decreased sodium reabsorption), sodium losing renal diseases (nephritis, salt wasting nephropathy), addison's disease (lack of aldosterone)
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treatment of hypovolemic hyponatremia
1. hemodynamically unstable 2. CNS symptoms present 3. rate of sodium replacement
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if hemodynamically unstable
restore intravascular volume 1st (NS or LR 200-300mL/hr, faster if need more volume
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No CNS symptoms)
restore ECF volume deficit=ECF norm-ECF current(use ABW even if >130%), kg * 0.2, give NS or LR at 100-150 mL/hr for L needed
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CNS symptoms present
restore sodium deficit, endpoint 120-125 mEq/L or until symptoms abadate, use CBW or ABW
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restoring sodium deficit with CNS symptoms, acute
<48 hours, NaCl infusion or 3%, calculate change in serum sodium=mEq Na/L in replacement IV-serum Na/(TBW +1), 1. replace with 0.9 plus or minus loop diuretic 2. replace with 3%(potential for error is higher), (513mEq/L plus or minus loop, MUST use infusion pump to deliver no faster than 1-2 mL/kg/hr inititially for first 1-3 hours(100-150mL/hr) 3. check serum sodium q 2-4 hours titrate infusion to raise serum sodium no faster than 2 mEq/L/hr
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restoring sodium deficit with CNS symptoms, chronic
>48 hours, 1. estimate volume of NaCl infusion req to restore sodium deficit using normal saline,2. replace 1/2 over 1st 24 hours and remainder over next 24-72 hours 3. check serum sodium q 4-6 hours initially, titrate infu to raise serum sodium no faster than 0.5mEq/L/hr
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maxiumum rate to replace serum sodium to prevent osmotic demyelination syndrome and both acute and chronic
no more than 8-12 mEq/L/day
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isovolemic (euvolemic) hyponatremia
normal total body sodium and a small increase in total body water, ALWAYS an imbalance of water intake and excretion due to 1.altered thirst 2. inappropriate ADH secretion, 3. defective renal diluting mechanisms
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conditions assoc with isovolemic hyponatremia
severe hypothyroidism, GC deficiency, psychogenic water drinking(>20L/d), SIADH
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diagnostic clues of euvolemia
Uosm>>100mOsm, UNa>>20 mEq/L(very concentrated urine)
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etiologies of SIADH
cancer(secrete ADH), CNS disorders or insults, pulmonary, major surgery, pain, decreased solute intake
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drugs that can cause isovolemic hyponatremia
nicotine, opiates, cyclophosphamide, vinc/vinblastine, phenothiazines, tricyclics, MAOI, carbamazepine, NSAIDs, desmopressin, oxytocin, ecstacy, SSRIs
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treatment of isovolemia hyponatremia, moderate to severe CNS symptoms (agitation, seizures, delirium)
fluid restrict to 1-1.5 L/d plus or minus furosemide (20 mg q 4-6 hours) 1. correct with 3%(need to use), endpoint 120-125mEq/L, must use infusion pump to deliver NFT 1-2cc/kg/hr initially, monitor Na, VS, sx, and fluid status q 2-4 hours in first 24 hou, titrate to raise NFT 1-2 mEq/L/hr in first 24 hours and then decrease over remaining 24 hours
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2nd option for mod-sev CNS symptoms with isovolemic hyponatremia
AVP receptor antagonsits (aquaretics)-contra in hypovolemia, conivaptan or tolvaptan
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treatment of isovolemic hyponatremia, asymptomatic or mild CNS symptoms
fluid restrict 1-1.5 L/day plus or minus demeclocycline 300 mg qid-blocks effects of ADH in collecting ducts, onset 3-6 days(long) or plus or minus increase solute ingestion and increase free water excretion by increasing salt intake (2-3 gm over usual + lasix) or urea 30gm/d
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hypervolemic hypotonic hyponatremia
increased total body water and sodium but water>>sodium
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conditions associated with hypervolemic hypotonic hyponatremia
CHF, syndromes assoc with decreased plasma alb (cirrhosis, nephritic syndrome, malnutrition), chronic renal failure(renin-angio system), pregnancy(increased blood volume)
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treatment of hypervolemic hypotonic hyponatremia
correct underlying cause, fluid restrict, saline restrict(<2.4g/d), loop diuretics (increase free H20 excretion)
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hypernatremia
>145 mEq/L, always hypertonic-reflects a water deficit relative to sodium, classify according to volume status
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initial signs and sx of hypernatremia
thirst, fever, NV, Gi cramping, lethargy
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neurologic symptoms of hypernatremia
only if acute increase in serum sodium, altered mental status, irritability, restless, muscle spasm, hyperreflexia, spaticity, seizures, coma, death
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treatment of hypernatremia
slow correction is mandatory as rapid lowering may result in cerebral edema, seizures, permanent neurological sequelae and death can occur
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hypovolemic hypernatremia
TBW loss
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renal causes of hypovolemic hypernatremia
diuretics, glycosuria, acute/chronic renal failure
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non-renal causes of hypovolemic hypernatremia
adrenal, GI losses, repiratory losses, skin losses
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treatment of hypovolemic hypernatremia
1. hemodynamically unstable, yes replace intravascular (200-300mL/hr with NS or LR, if not 2. replace TBW deficit
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TBW deficit for hypovolemic hypernatremia
TBW deficit(L)=Current TBW x [(na/140)-1], use CBW or ABW, replace with , use D5W(0 mEq/L) or 0.45(77mEq/L), or oral water, double check with change in serum sodium=mEq Na/L in replacement IV-serum Na conc/TBW +1
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infusion rate of replace TBW deficit in hypovolemic hypernatremia
1/2 over first 24 hours, remainder over next 24-72 hours, monitor Na, fluid status, sx q 2-4 hours x 1st 24 hours
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rate of correction of hypovolemic hypernatremia, acute
<24 hours-serum sodium should decrease NFT 1mEq/L/hr
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rate of correction of hypovolemic hypernatremia, chronic
>24 hours, serum sodium should decrease NFT 0.5 mEq/L/hr
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targer serum sodium of hypovolemic hypernatremia
Na<145 mEq/L, replace ongoing water loss
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isovolemic hypernatremia
clinically euvolemic, total body sodium normal; small volume of pure water loss
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causes of isovolemic hypernatremia
central diabetes insipidus(insufficient amt of ADH),nephrogenic diabetes insipidus(kidneys don't respond to ADH), drugs(demeclocycline, lithium, phenytoin, clozapine), high insensible loss(skin and respiratory), Iatrogenic(insufficeient fluid intake)
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treatment of isovolemic hypernatremia
calc water deficit and correct with free water, treat underlying cause
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treatment for diabetes insipidus
desmopressin (DDAVP), aqueous vasopression (ADH), chlorpropamide(increase kidney's response to ADH), clofibrate(increase ADH release), carbamazepine(increase response to ADH), HCTZ(increase sodium excretion), indomethacin(inhibits PG in kidneys(increase ADH effect)
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hypervolemic hypernatremia
increased total body sodium>>increased total body water
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causes of hypervolemic hypernatremia
iatrogenic, MC excess(primary aldosteronism, cushing's syndrome, congenital adrenal hyperplasia, admin of GC or MCs)
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treatment of hypervolemic hypernatremia
d/c offending hypertonic agent, diuretics(loops and thiazides), hemodialysis(with acute renal failure)
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