welcome to another MedCram lecture we're going to talk about hyperkalemia
hyperkalemia like anything else that ends in e mia has to do with the blood
and the k if you remember from the periodic table has to do with potassium
so we're going to talk about high potassium in the blood and that
generally speaking is greater than 5.0 but of course the higher it goes the
worse the symptoms can become so the normal range for potassium is about 3.5
to 5.0 this is an extremely well regulated system potassium has to be
very well regulated in the blood and the reason is is because the conduction
system in the heart specifically and also in the muscle
depends heavily on potassium going through the membrane and so the
conductivity to potassium is very high so that if there is a problem with the
concentration of potassium outside the cell it's really going to affect the
depolarization of those cells and so potassium abnormalities are really going
to hit the heart quite hard and cause arrhythmias and that's why the body is
so keen on protecting the level of potassium so we're gonna talk about the
causes of hyperkalemia the manifestations of hyperkalemia and the
treatment of hyperkalemia okay so let's talk about the causes the first cause is
excessive tissue release or trans cellular shifts okay so you can think
about for instance diabetes remember what happens in diabetes is there's a
lot of glucose around the cells so you've got a cell here and you've got
glucose outside the cell and that causes water to leave the cell and for it's
something to do something called coronation shrinks basically and when
that happens the potassium concentration which is already high in the cell is
actually going to go up and this causes leakage of potassium outside the cell
and the fact in diabetes is insulin which especially in type 1 diabetes
is rare and insulin is responsible for putting potassium back inside the cell
okay so that's an important note is that insulin causes potassium to shift back
into the cell and in a patient with diabetes the glucose is high that causes
eventually potassium to leak outside the cell since there's no insulin it cannot
be put back inside the cell another corollary to this is something called HH
or hypo Ren anemic hypo aldosterone ism okay so that's hypo renin the renin is
the thing that this should be stimulating the adrenal cortex to make
aldosterone but as a fact that it doesn't you get hypo aldosterone
now remember aldosterone works on the distal convoluted tubules
right about there and remember what it does it causes potassium excretion and
sodium reabsorption at the distal convoluted tubules
so if you don't have enough aldosterone being secreted from the zona glomerulosa
of the adrenal cortex you're gonna get an accumulation of potassium inside the
serum the reason why I bring this up together is this hypo Renick hypo
aldosterone ism can be seen together with diabetes
so that's just one cause of hyperkalemia the next cause is kind of obvious and
that's just increased intake of potassium so you got to kind of know
what has potassium in it and some of the things that have potassium in it our
salt substitute so instead of having the cation sodium that has the cation
potassium the other thing that you can see is the excessive intake in renal
failure these people who are in renal failure typically are the ones that are
on salt substitutes and this potassium cannot be cleared the other one that we
kind of talked about if the zona glomerulosa of the adrenal cortex is not
secreting aldosterone is you will see adrenal failure this is otherwise known
as Addison's disease however if it is a problem with the pituitary not
stimulating the adrenal cortex the aldosterone still is secreted in
sufficient amounts that you may not see hyperkalemia however if there is a
direct attack on the adrenal cortex where antibodies are destroying all
three layers then your aldosterone levels will be low and you will see
hyperkalemia in addition to all of the other things that you would see in
adrenal failure for instance hypoglycemia hyponatremia and metabolic
acidosis the last thing that you would see is of course in a potassium sparing
diuretic so some examples of this would be spironolactone or a miller ID
incidentally other medications that could also increase your potassium are
things that can also affect shifting of the cells or affect the other areas that
we've already talked about the ones that you should know about our ACE inhibitors
so remember ace inhibitors inhibit a switch is angiotensin converting enzyme
which is in the lungs and that's going to affect the ability to make
aldosterone the other thing that can do this is beta blockers we'll talk about
treatment with beta agonists later but beta blockers can affect shifting of
potassium and actually caused it to go out of the cell another cause is
something that's interesting and it's called pseudo hyperkalemia and it's
really based on the fact that all cells in the body have high concentrations of
potassium in it so where you see this is if you have a patient with many cells
that are drawn in a test tube so if you have marked leukocytosis or
thrombocytosis so they'll be in platelets as well and you get
coagulation in the test tube that causes these cells to lyse and release their
potassium when you put this through the laboratory
equipment you're gonna see elevated potassium and they'll sometimes tell you
if they see this and they'll say hemolysis and if you get hyperkalemia
and they say by the way hemolysis was three plus then you may have to take
that with a grain of salt so to speak and maybe repeat the test again to see
and redraw the blood actually because if once there's human lysis you really need
to get a new blood draw on that specimen okay let's talk about manifestations of
hyperkalemia what would happen really has a lot to do
with the heart and the reason is is because the conductance of potassium in
the depolarization of cardiac conduction cells is quite high such that potassium
is always leaving the cells and so what happens is you have a positive charge
leaving the cell okay what's that going to do that's going to generally make the
inside of your cell negative and that's exactly what we see here down to close
to negative 90 millivolts you've got this negative the problem here is is
that when you have an abundance of potassium in the solution in the serum
in other words when you have hyperkalemia these potassium ions are
not going to leave the cell as quickly and so whereas you would have a very
negatively charged cell it's not going to be so negatively charged you're going
to get something called depolarization so these cells are more excitable and as
a result of that not only is it depolarized
but instead of having a nice sharp uptick it's going to come up more slowly
and the repolarization is going to be somewhat dampened okay as a result of
that when you look at a nice QRS complex instead of having a discrete P wave q r
s t what you're actually going to see is the P wave is almost going to be
non-existent the R wave is going to sort of come up slightly you're gonna have
this s depression and then this T wave and it's almost gonna look sinusoidal
and of course the higher the potassium and the faster the potassium has gotten
high the more quickly you're gonna see this if somebody is camping out at five
to six and they go up to seven you're not gonna see those changes because the
body has a chance to adjust perhaps but if someone is living in the 3s two fours
and then jumps up to seven you're more likely to see that the first thing that
you'll see with hyperkalemia is you'll actually see peaked t-waves
okay that's the first thing that you'll see and then eventually you'll just see
this thing go sinusoidal so it'll just kind of go like this and you'll just go
into cardiac arrest so what should you know about manifestations you will have
depolarization due to low potassium conductance lower than normal and then
after that you'll get hyper polarization due to inactivated sodium channels
you'll have this reduced phase zero velocity okay and you'll have decreased
membrane excitability and then you'll get increased potassium conductance and
accelerated repolarization okay so what should you know what would they actually
test you on a test about hyperkalemia I think the thing that they would test you
on is number one no that peaked t-waves is the first sign that you'll see number
two if it eventually gets high enough you'll get this sinusoidal wave and
number three hyperkalemia in general is going to affect the heart and all of
this is an emergency now in the next video we're going to talk about the
treatment of hyperkalemia and some of the reasons why this treatment works
you