Electrolytes Overview

Electrolytes that are primarily found in the ECF and ICF compartments

  • ECF
    • Na, K, Ca, Mg
    • Cl, HCO3, PO4, SO4
  • ICF
    • K, Mg
    • PO4, SO4

Relationship between serum sodium concentration and TBW

  • Plasma osmolality is determined by ratio of plasma solutes (Na) and plasma water
    • The body regulates water to maintain plasma osmolality
      • An increased (Na) serum osmolality results in TBW depletion   (deydration)
      • A decreased (Na) serum osmolality results in TBW excess        (CHF, cirrhosis)

serum osmolality

Plasma osmolality = 2 [Na] + [glucose]/18 + [BUN]/2.8

  • normal plasma osmolality = 280-300 mOsm/kg
  • Can be used to determine osmolar gap (allows you to determine if there is something poisoning the patient–ethanol, methanol, isopropanol, antifreeze, lorazepam, mannitol)
  • Can also be used to determine deviations in TBW content

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