15 Na Disorders
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both results lead to brain symptoms
Hyponatremia
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Plasma osmolality
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albumin minor contributor, not in equation, more important for oncotic pressure
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substances interfere with Na measurement
triglycerides
post-TURP
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low osmolality: unknown cause
Low usine osm: post TURP, beer potomonia
Urinary Sodium
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in reality, no normal levels because varies
intake equals excretion
urine Na < 10: extrarenal including CHF, cirrhosis, nephrotic syndrome
urine > 20: renal including AKI, CKD
Patients with SIADH are typically euvolemic; therefore, urine sodium concentration is typically elevated (>40 mEq/L), unlike in patients with hypovolemia.
Urinary Osmolality
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ADH controls above 3 tests
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if body responding appropirately
urinary Na may vary with dietary intake
Causes
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HF
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high Uosm because ADH high
Renal Failure
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renal failure: concentrated urine even at baseline. Can't excrete water
Diuretics
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hyponatremia common with thiazides
loop diuretic effect:
decreased Na absorption, increased osm at CD, decreased Na/water absorption
interstitial high osm eliminated, lower driving force to remove water
result: very hard to reabsorb water and become hyponatremic
thiazide:
Na blocked, increased osm at CD, decreased water/Na absorption
medullary osm intact: continue to maintain ability to absorb free water
result: excrete Na but absorb water = hyponatremia
ADH
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reason why athletes drink Gatorade and not water
hypothyroidism: high ADH with low thyroid
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no crackles, ankle edema
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stroke, brain bleeds, tumor
any kind of pulmonary diseases, small cell lung cancer
Inappropriately wet head: cyclophosphamide can cause hyponatremia due to SIADH
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clinical euvolemia: absence of signs
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Psychogenic
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Diets
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common theme: little Na ingestion
kidney must maintain minimum osm
pt on restricted diet can only excrete 10 water
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Summary
Volume and Osm
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hypervolemic: physical exam signs
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low Uosm: kidney response normal
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measure UNa to differentiate
ADH and Osm
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red
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Treatment
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acute hyponatremia: correct as fast as can (e.g. surgery causes low Na)
chronic hyponatremia: correct slow
high risk: alcoholics, liver disease, malnutritioned, hypokalemia
10 meq correction 1st day
Hypernatremia
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DI
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hypernatremia happen in central lesion
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won't raise bp
thiazide, endomethacin (NSAID), amiloride
Treatment
calculate free water deficit
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