Potassium
[KB2:p15-16]
Total K+ in body
= 40-45mmol/kg
Body distribution
ICF = 90%
ECF = 2%
Bone = 8%
Measurement of total body potassium
Isotope 44K
* Used to measure total body potassium, including bone
* Naturally occurring
Isotope 42
* Injected to measure total exchangeable potassium pool, excluding bone
Treatment options
IV calcium
For severe hyperkalemia
- Does not alter [K+] level
- Increased [Ca2+] stablises the myocardial membrane and decrease risk of serious arrhythmia
- Calcium gluconate 10% 20mL over 2-5minutes
Glucose and insulin
- Rapid onset but short duration
- Shifts K+ intracellularly
- 25 grams of IV dextrose (50mLs of 50%) with 10unit of S/C insulin
Sodium bicarbonate
- Shifts K+ intracellularly
- Also rapid onset and short duration
Resonium
- Resin exchanges 1mmol of K+ for 1 mmol of Na+ for every gram of resin
- Exchange occurs in colon
--> Slow onset
- Net loss of K+ and net gain of Na+
Dialysis
- Preferred option in severe chronic renal failure and acute renal failure
????Salbutamol
Other notes
During exercise
- K+ moves out of active muscle cells due to rapidly firing action potentials
- Epinephrine stimulates uptake of K+ by other cells, which blunts the increase.
Buffering
- Potassium moves in and out of muscles
- --> Buffering of ECF [K+] on a moment to moment basis
[K+] and [H+]
- Increase in ECF [H+] is associated with increase in ECF [K+]
- And vice versa
- [AV6:p136] Mechanism - uncertain