Potassium is the major intracellular cation (sodium is major extracellular). 90% is exchangeable (70% for sodium)

  • Equilibrium potential of -90mV
  • Total body = 45mmol/kg (2800 mmol per average male)
    • ICF     90% 150-160 mmol/L
    • ECF    2%    3.5-5.0 mmol/L
    • Bone  8%
  • Completely and passively absorbed in upper GI tract
  • Excretion: Mainly in collecting ducts. Affected by aldosterone (collecting duct regulator)

Association with pH
  • Serum K is inversely related to serum pH
  • Serum K decreases by 0.3mEq/L for every 0.1U increase in pH above normal
  • Alkalosis:
    • Correction of an alkalotic pH will produce a rise in serum K
    • Alkalosis (increase pH) shifts K intracellularly, lowering serum K
  • Acidosis
    • Shifts K to intravascular space so increasing the serum K
    • Correction of acidosis will produce a decrease in serum K (may drop precipitously eg correction of DKA)

  • Major intracellular ion affecting tonicity
  • Antiport molecule in Na/K transport and control of intracellular volume
  • Involved in neuromuscular excitability
  • The gradient across cell membranes determines the excitability of nerve and muscle cells including myocardium
  • Regulation of some intracellular processes (protein/glycogen synthesis, carbohydrate metabolism)
  • Of all the electrolytes, rapid changes in potassium concentration can cause the most immediate life threatening emergencies

CCC 700 6

Critical Care


BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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