15 Na Disorders

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• both results lead to brain symptoms

Hyponatremia

Plasma osmolality

• albumin minor contributor, not in equation, more important for oncotic pressure

• 1.6 meq/L decrease in Na for every 100mg/dL increase in glucose

• substances interfere with Na measurement
• triglycerides
• post-TURP

• low osmolality: unknown cause

• Low usine osm: post TURP, beer potomonia

Urinary Sodium

• 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

• ADH controls above 3 tests

• if body responding appropirately
• urinary Na may vary with dietary intake

Causes

HF

• high Uosm because ADH high

Renal Failure

• renal failure: concentrated urine even at baseline. Can't excrete water

Diuretics

• 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 and SIADH

• reason why athletes drink Gatorade and not water

• hypothyroidism: high ADH with low thyroid

• no crackles, ankle edema

• stroke, brain bleeds, tumor
• any kind of pulmonary diseases, small cell lung cancer

• Inappropriately wet head: cyclophosphamide can cause hyponatremia due to SIADH

• clinical euvolemia: absence of signs

Psychogenic

Diets

• common theme: little Na ingestion
• kidney must maintain minimum osm

• pt on restricted diet can only excrete 10 water

Summary

Volume and Osm

• hypervolemic: physical exam signs. Use loop diuretics and not thiazide

• Mostly hormone derangements
• low Uosm: kidney response normal

• measure UNa to differentiate
• hypovolemic: Low sodium, low water, but a lot less Na
  • diuretics, adrenal insufficiency (acidosis, hyperkalemia), GI loss, 3rd spacing (pancreatitis)
  • Treat with NS

ADH and Osm

• red

Treatment

• 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

DI

• hypernatremia happen in central lesion

• won't raise bp

• thiazide, endomethacin (NSAID), amiloride

Treatment

• calculate free water deficit

$$ Water\ deficit = \frac{[Na]-140}{140} \times TBW $$