Cardiac Arrest. Hyperkalemia
is high potassium in the bloodstream.
Normally, potassium is very narrowly
controlled in our blood stream. A lot of potassium
inside our cells, but not a lot in
the bloodstream itself. And the kidneys are responsible
for excreting potassium and our gut
is responsible for absorbing potassium.
And our bodies homeostatic mechanisms
are in place to control the level of potassium.
But if potassium is given by the physician
or through some error
by a nurse in the ICU, or
if you give Succinylcholine to the wrong patient,
you can have a very sudden increase in potassium.
So normally a potassium, we'll say,
runs around 4 mEq/L.
If you give that patient, normal patient,
Succinylcholine, their potassium will go up to about
5 mEq/L, which is not a problem.
If however you start at a higher level,
for instance in a patient with a renal failure who
hasn't been recently dialyzed, let's say it starts
at 6, and you give them Succinylcholine, it may
go up to 7 or 8 and there'll be a cardiac arrest.
In addition, if you give Succinylcholine
to people who have
conditions such as neurologic problems,
massive trauma, spinal cord injuries,
recent burns, burn in the last year
actually, or renal failure,
there can be a huge release of potassium into the bloodstream.
And what happens with the ECG,
and it happens over a minute or two,
is the t-waves, which is the last wave
in the normal complex of the ECG suddenly
become peaked, and then the whole
complex starts to widen. And then you can
get what's called a sine-wave where
the, it looks kind of like this, it looks like waves
on the sea. And then asystole. An asystole
is complete loss of contraction of the heart,
complete loss of electrical activity
in the heart. What happens with Hyperkalemia is,
there's a change in the ratio between the resting potential
and the threshold potential in the sino-atrial
node, which controls our
heart rate. This is a complex concept and I'm not
going to spend a lot of time on it because
it really requires you to sit down and read
in detail if you're interested. But what happens
is that, by changing the ratio
of resting potential
to threshold potential, the heart
is unable to produce electrical
signal that will cause an action potential
and cause a wave through the heart.
The only treatment for this that works
quickly is to either lower the potassium,
and unfortunately it's hard to do that quickly,
or to give a drug that interacts with potassium
to change that ratio of threshold
to resting potential
back towards normal. And the drug that
you gave is Calcium. Calcium is never given
in normal cardiac arrest situations, because
in ischemic cardiac arrest it can actually
cause cell death and it no longer exists
on the ACLS protocol. So this is an asystolic
cardiac arrest where you don't use
the ACLS protocol, you use calcium.
This will very rapidly change that ratio
and amazingly, the normal heart
rhythm will come back again. It doesn't however
have any effect on the elevated potassium
level in the blood. And you must treat that. And there are
a number of ways of treating that, including hemodialysis
in which you actually take the potassium
right off. You can give glucose
or insulin intravenously and that drives
potassium back into the cells. Or,
if you've got a patient where it's not a huge problem, it's not
that badly elevated and you just want to bring it down
over a couple of days, you can use an exchange
resin such as Kayexalate orally.
And that'll help clear the potassium
out of the system.
So hyperkalemic cardiac arrest is,
as I mentioned, it's an uncommon
event, but I've seen it several times. It does not
follow the ACLS guideline, so you have to be
aware of that. The treatment
of the Hyperkalemia is necessary
even if the patients return to a normal heart rhythm. So you
can't forget that! And I've seen one death because
the physician involved sent a patient to the ward
assuming that, because the rhythm
was back to normal, all was well. And the patient
had a recurrence of the hyperkalemic
cardiac arrest on the ward
and unfortunately didn't survive.