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 going to 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 transcellular 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 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 diabetics 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 going to get an accumulation of potassium inside the
serum the reason why I bring these 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 in 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 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 going to 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 up tick 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 going to
have this s depression and then this T wave and it's almost going to look
sinusoidal and of course the higher the potassium and the faster the potassium
has gotten high the more quickly you're going to see this if somebody is camping
out at five to six and they go up to seven you're not going to see those
changes because the body has a chance to adjust perhaps but if someone is living
in the three s 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 you 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