The beauty of the body is the symmetry. Hyperkalemia is simply the reverse of hypokalemia. Normally potassium is 150mEq/L on the inside and 5mEq/L on the outside with a 90mV electric potential on the inside. Let’s pretend the potassium levels start to increase in the ECF. That’s going to make potassium start to flow inside. What’s that going to do to the voltage of the cell? It’s going to make it less negative than normal and the term we use for that is depolarized. Why? Because potassium is positively charged!
The Effects of Hyperkalemia
Clinical manifestations: Generalized stimulation of the nervous system and muscles. EVERYTHING speeds up.
1) irritability and anxiety
2) muscle twitches
3) heart flutters and fibrillations
4) increased GI motility
Who develops hyperkalemia? What causes hyperkalemia?
1) Kidney failure is the most common cause of hyperkalemia. Ever heard that banana’s are high in potassium? How come there’s no warning label on every Chiquita banana? If banana’s are high in potassium and you eat 3 bananas in a row, what happens? Your kidneys will excrete that potassium. As long as your kidneys are working, there’s no warning label on the banana. If your kidneys are not working, you have to be very careful about what you eat.
2) Excessive IV administration of K+: If the nurse doesn’t set the drip rate properly and it drips faster than the kidneys can excrete, then hyperkalemia will develop. If you think that doesn’t happen often… let me explain something: The IV bag for sodium chloride (saline solution) is in black. The reason why they write potassium chloride in red nowadays is because nurses used to mix them up and assume sodium chloride couldn’t be much different than potassium chloride and kill people! When a healthcare provider causes the death of a patient, that’s called iatrogenic death.
3) hypoaldosteronism: Again, when we discussed hypokalemia, we explained this hormone is involved with the regulation of the K+/Na+ levels and we’ll talk about it more in the future.
Treatment for Hyperkalemia
The treatment for hyperkalemia is much more complicated than hypokalemia. In hypokalemia you just drink more electrolytes.
1) Give diuretics. Remember that the use of diuretics is the cause of hypokalemia, so you could imagine to reduce hyperkalemia, a diuretic would do the trick as well.
2 Give ion-exchange resin such as Kayexalate which is a jello the patient swallows. Once it’s in their intestine, it draws potassium out of the blood stream and it binds to the jello and they poop it out.
3) Hemodialysis: What people with failing kidneys do is they have a semi-permanent shunt (a U-shaped tube) in their wrist and every other day they hook them up to this machine that filters their blood for them. If they don’t do this every other day, they will be dead in three days. That’s why these people are waiting eagerly for a kidney transplant.
The problem is ALL these things take hours. Diuretics, dialysis and ion-exchange resin take hours. The problem is, if their heart rate is speeding up and fibrillating, you only have a matter of minutes. The only method that would work in an emergency is to give calcium gluconate. It does not have an effect on potassium levels in the blood, but it reduces the excitability of cardiomyocytes thus lowering the likelihood of developing cardiac arrhythmias.
Here’s a graph because graphs are given to summarize relationships.
On the X axis we have the potassium ion concentration in the ECF. We could see it’s 2, 5, 10 and so forth (remember the normal is around 5). On the Y axis we have the membrane potential (mV). This is a linear relationship, a mathematical relationship predicted by the Nernst equation. If the K+ is at 5, the mV is around -90mV.
What if the potassium level dropped? (hypokalemia). If the K+ is at 1.0, the voltage has gone to -110 mV and hyperpolarized (become more negative than normal, everything slows down).
What if the potassium increases to 10? (hyperkalemia). Then we are at a voltage of -70mV and the cell membrane is depolarized (less negative) causing everything to speed up speed up speed up.
Now it’s time to talk about the next topic, ACTION POTENTIALS!