15 Na Disorders

  • 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=[Na]−140140×TBWWater\ deficit = \frac{[Na]-140}{140} \times TBW