April 27, 2016 - Hypokalemia

Question 1

Low [K⁺] and Aldosterone

Answer 1

Low potassium levels should turn off aldosterone to help preserve potassium.

The TTKG of cells should be low (

Question 2

TTKG

Answer 2

TTKG = (Urine_K x Serum_osm) / (Serum_K x Urine_osm)

Question 3

Hypokalemia and TTKG

Answer 3

In the presence of hypokalemia, a TTKG > 4 is abnormal and indicates that the principal cell is to blame.

TTKG should be less than 4 because the body should be trying to conserve what little potassium it has left.

Question 4

Hypokalemia Scheme

Answer 4

Question 5

RBC Production and Hypokalemia

Answer 5

If you are producing cells very quickly, all those cells need to have potassium inside and will steal potassium from the extracellular space.

Question 6

Refeeding Syndrome and Potassium

Answer 6

Refeeding can also cause a drop in potassium because of the highly sensitive insulin receptors. The insulin acts very effectively and causes a drop in potassium.

This works because insulin works on the sodium hydrogen exchanger which brings more sodium into the cell which allows the sodium potassium ATPase to work more effectively and pump more potassium into the cell which lowers extracellular potassium levels.

Question 7

Potassium and Resting Potential

Answer 7

Hypokalemia will cause a lower (more negative) resting potential for the cell. This takes longer for the cell to repolarize, making it not work effectively.

Hyperkalemia will cause a higher (more positive) resting potential for the cell. This theoretically allows the cell to work better, however the passive sodium channel becomes deactivated and the cell works less effectively.

Question 8

ECG Changes of Hypokalemia

Answer 8

T-wave flattening (longer to repolarize)

QT prolongation (longer to repolarize)

U-wave (depolarization of the Purkinje)

ST depression and T-wave inversion

* ECG changes are BAD - MEDICAL EMERGENCY *

Question 9

Treatment of Hypokalemia

Answer 9

If it is life-threatening, you need to supply intravenous potassium at a rate of 1 mmol/min and adjust the rate when potassium levels are >3.

If non life-threatening work to correct the underlying cause.

Question 10

Spironolactone MOA

Answer 10

Inhibits the aldosterone receptors in the cell. This prevents sodium re-uptake in the principal cells and therefore the wasting of water and sodium.

Question 11

Aldosterone Action

Answer 11

Acts on the distal tubules and collecting ducts of the nephron, increasing reabsorption of ions and water in the kidney.

Causes the conservation of sodium, the secretion of potassium, an increase in water retention, and an increase in blood pressure and blood volume.

Question 12

Hypokalemia and Hypomagnesemia

Answer 12

If you are treating hypokalemia also think about treating hypomagnesemia.