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