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Sodium abnormalities

Key points

  • Normal sodium is 135-145
  • When approaching sodium abnormalities always get urine electrolytes!
    • Urine Na
    • Urine osmolarity
  • Complications with correcting too quickly
    • If Na levels are rapidly increased, this will increase the risk of developing central pontine myelinolysis
      • Rapid increase in serum Na causes efflux of water from the intracellular space into the serum –> dehydration of and damage to the myelin sheath of nerves in the central region of the pons
    • If Na levels are rapidly decreased, this will increase the risk of developing cerebral edema
      • Water quickly rushes in from the extracellular space to the intracellular space causing edema
  • Common blood work with any electrolyte abnormality
    • CBC and extended electrolyte panel
    • Serum osmolality
    • Urine osmoalality
    • Urine Na
    • Serum measurement of
      • Urea
      • Glucose
      • Uric acid
      • Total proteins
      • Triglycerides
    • TSH
    • Cortisol

Hypernatremia

  • If Na > 145 it is likely due to a lack of water than an excess of Na
  • Populations in which water deficit is seen
    • Elderly
    • Dementia
    • End of life
  • Management
    • Treat with D5W and 2/3 and 1/3
    • If they are hypervolemic then you can add furosemide as well

Hyponatremia

  • Serum osmolarity = 2 x Na + glucose + BUN
    • Mnemonic is 2 salts and a sticky BUN
  • Types
    • Isotonic hyponatremia
      • Laboratory abnormality seen in patients with hyperlipidemia or excess proteins in the serum
    • Hyperosmolar hyponatremia
      • “Pseudohyponatremia”
      • Something else other than Na like BUN or glucose is increasing the osmolarity causing dilution of Na
    • Hypoosmolar hyponatremia
      • True hyponatremia
  • Urine sodium and urine osmolality
    • Urine Na
      • If RAAS on, then urine Na low (urine Na < 20)
      • If diuretics are being used then urine Na will be high regardless of RAAS
    • Urine osmolarity
      • If ADH is not suppressed and is turned on, then urine osmolarity > 100
  • Types of hypoosmolar hyponatremia
    • Hypervolemic
      • Commonly seen in
        • Cirrhosis
        • Heart failure
        • Nephrotic syndrome
      • The effective circulating volume decreases triggering ADH (which increases the free water retained) and RAAS which increases Na and H2O retention
      • Urine Na < 20 (extrarenal) and urine osm > 100
        • This means that there is an extrarenal cause for the hyponatremia
        • Examples include
          • Heart failure
          • Cirrhosis
          • Nephrotic syndrome
        • Kidneys are able to reabsorb Na but there is a low circulating effective volume due to the activation of RAAS
      • Urine Na > 40 (renal)
        • This suggests that there is a renal cause of the hyponatremia
    • Euvolemic
      • Urine osmolality is a marker of ADH secretion
      • Urine Na < 20 AND urine osmolality < 100 mOsm/kg (low ADH) – these people have a RELATIVE SALT DEFICIENCY
        • Despite the fact that these patients’ have their RAAS systems turned off, their urine Na is still low
          • They are relatively Na deficient compared to their water stores and do not have enough Na to excrete
          • They produce very dilute urine
        • Common causes include
          • Primary polydipsia
          • Beer drinkers’ ptomania
          • Tea and toast diet
      • Urine osmolality > 100 mOsm/kg (high ADH)
        • ADH is turned on!
        • Common causes include
          • Hypothyroidism
          • Primary adrenal insufficiency
          • SiADH (diagnosis of exclusion)
    • Hypovolemic
      • Urine osm > 100 and Urine Na < 20 (extrarenal)
        • Also associated with low urine output
        • Gastrointestinal losses such as
          • Vomiting
          • Diarrhea
      • Urine Na > 40 (renal)
        • Use of diuretics
        • Cerebral salt wasting (consider in the case of hyponatremia if there is CNS disease)

Credit for this wonderful table to CritlC, their youtube video explaining this is very good as well! https://www.youtube.com/watch?v=dmM2K50bnKw

SiADH

  • It doesn’t take much for ADH to be secreted
    • Pain
    • N/V
    • Medication
    • Tumors
    • Adrenal insufficiency
  • Treatment
    • Fluid restriction
    • Furosemide may also be used to increase water diuresis