Topic 1.69 - Disorders of potassium balance. Hypo- and hyperkalemia

What is the normal potassium concentration in the blood? What is the normal intracellular potassium concentration?

Blood

-3.5-5.5 mM

Intracellular

-140-160 mM

What is meant by intrinsic and extrinsic potassium balance?

Intrinsic

-distribution of potassium between the intracellular space and extracellular space

Extrinsic

-ratio of potassium intake and potassium loss

What are 6 determinants of intrinsic potassium balance?

pH

Extracellular (hyper)tonicity

Insulin

Catecholamines

Mineralocorticoids

Physical exercise

What happens to potassium concentration in acidosis and alkalosis?

Acidosis -> hyperkalemia

-cell take up H and release K

Alkalosis -> hypokalemia

-cells take up K and release H

How does extracellular hypertonicity affect potassium concentration?

Water moves out of the cells -> higher K concentration within cells -> K flows out of the cell -> potential hyperkalemia

How does insulin affect potassium concentration?

Enhances function of Na/K APTase -> more K enters cells

How does physical exercise affect potassium concentration?

Causes K outflow from muscle cells

What is the normal daily intake of potassium?

40-120 mmol

What are 5 determinants of external potassium balance?

K intake

Mineralocorticoids

Filtration

pH

GI excretion

How does GFR affect potassium (3)?

•Increased GFR -> increased Na/K exchange

•Increased flow rate -> inhibition of reabsorption

•Increased level of anions -> increased K excretion to maintain electroneutrality

What may happen to GI excretion of potassium in renal failure?

May increase from 10% to 50%

When is hypokalemia severe?

<2.5 mM in blood

What are the 3 most important causes of hypokalemia?

Increased loss of K

-diuretics - most common

-diarrhea, vomiting

-hyperaldosteronism

K shift into cells

-alkalosis

-exogenous insulin

Decreased K intake

What are 4 consequences of hypokalemia?

Development of metabolic alkalosis

Hyperpolarized membranes

ECG changes

Polyuria

What are 3 symptoms of hyperpolarization of membranes?

Muscle weakness

Muscle cramps, pain

Cardiac arrhythmias

What are 3 ECG changes seen in hypokalemia?

Shallow or inverted T-wave

Prominent U-wave

ST-depression

When is hyperkalemia severe?

>7.0 mM in the blood

What are 3 causes of hyperkalemia?

Pseudohyperkalemia - due to cell death

Decreased loss

K shift out of cells

What are 4 causes of decreased loss of potassium?

Renal insufficiency

Addison disease

Potassium-sparing diuretics

RAAS inhibitors

What are 4 causes of K shift out of cells?

Acidosis

β blockers

Cell lysis

Increased intake in case of renal disease

What are 3 consequences of hyperkalemia?

Development of metabolic acidosis

Hypopolarized membranes

ECG changes

What are 3 symptoms of hypopolarized membranes?

Muscle weakness

Muscle cramps, pain

Cardiac arrhythmias

What are 3 ECG changes seen in hyperkalemia?

Peaked T-wave

ST-elevation

Wide QRS