Potassium

Overview

• 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)

Function

• 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

References and Links

• CCC – Hyperkalaemia management
• CCC – Hyperkalaemia DDx
• CCC – Hypokalaemia
• CCC – Hypokalaemia Mind Map
• ECG Library – Hyperkalaemia
• ECG Library – Hypokalaemia
• Clinical Case – Hyperkalaemia
• CCC – Potassium