Potassium is the major intracellular cation (sodium is major extracellular). 90% is exchangeable (70% for sodium)
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
Critical Care
Compendium
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 | On Call: Principles and Protocol 4e| Eponyms | Books |
MBBS FACEM DDU (Emergency) CCPU. Emergency Physician in Melbourne, Australia. Co-Ultrasound Lead for Emergency Medicine at The Alfred Hospital. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor of the LITFL ECG Library.
