Introduction to Defibrillation by Dr. Mjaye Mazwi.
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Hello my name is Mjaye Mazwi.
I'm a clinical fellow in cardiology here at Children's Hospital Boston, and I am going
to talk to you about defibrillation.
I am going to present the way that we think through defibrillation and the algorithm that
we use here at Children's.
You may have to modify this in some way to make this applicable to your setting.
Introduction: Defibrillation involves using direct currents to apply an electrical shock
shock to the myocardium.
It is an asynchronous shock, meaning that the shock is not timed to deliver any specific
point in the cardiac cycle, and the and the goal in delivering the shock is to depolarize
the myocardium and atrioventricular conduction.
The depolarization effectively resets the sinoatrial node allowing the restoration of
sinus rhythm.
The indications for defibrillation are ventricular fibrillation and pulseless ventricular tachycardia.
The first one is very intuitive and is the classic indication that everyone remembers.
The second is somewhat less intuitive but it's equally important.
Pulseless ventricular tachycardia we defibrillate, ventricular tachycardia with a pulse we cardiovert.
Equipment.
The basic functionality is all going to be encompassed in the box, which you see here.
It's extremely important that in whatever environment you practice you orient yourself
to the functions that are available in your unit.
There is considerable variation between manufacturers in where the buttons lie and how things are
adjusted.
And there is even considerable variation between models made by the same manufacturer.
Many hospitals, including Children's Hospital Boston, utilize more than one model, and so
in your environment to minimize the amount of time that you take to successfully defibrillate
your patient, do orient yourself to your machine.
That is because the most important determinant of your success with defibrillation is time
to defibrillation.
Delivering an appropriate shock to the myocardium as early as possible in this pathological
process is something that's likely to guarantee your success.
So starting out with the piece that interacts with the patient: the paddles or pads.
Both the paddles and the pads come in two sizes.
Looking first at our paddle, we have a pediatric paddle and we have an adult paddle.
This is a pediatric sized pad, and you can see when you compare it to an adult size pad,
how significant the difference in size is.
The cut off is weight.
We use the pediatric sized pads and we use the pediatric sized paddle for patients that
weigh 10 kilograms or less.
Any patient who weighs more than 10 kilograms, we should try to use an adult sized pad or
paddle.
It is very important to know exactly which one of the two is connected to your machine
before you deliver a shock.
There is no difference in efficacy between paddles and pads so you can use which ever
of the two you are most comfortable with.
It is extremely important regardless of whether you use pads or paddles to ensure that your
equipment has very good contact with the patient's skin.
When you are using pads this is extremely easy to do because of this extensive sticky
surface that conforms to the shape of the patient when the pad is applied.
With paddles it's much more challenging because the paddles have a rigid surface that does
not conform to the patient's shape.
The way that we get around this is we apply an electrostatic conductive gel to the paddle
before placing it in contact with the patient's body.
The electrostatic gel both insures a better footprint of contact and reduces the impedance
or the resistance to the electrical flow at the skin surface, ensuring a greater, effective
charge is delivered to the myocardium.
The reason contact is so important is twofold.
The first is that inadequate contact can result in the delivery of an inadequate shock.
The second is that if there's contact with only a small portion of the paddle or the
pad, the entire delivered shock passes through the small area of contact.
And what that does is that it significantly increases the chances of an entry burn where
that shock is delivered to the skin.
Additionally, it focuses the the electrical density of the shock and is much more likely
to cause myocardial damage in the path of that shock.
Moving now to the actual features of the box itself.
The key features of that are going to help you successfully defibrillate a patient are,
first of all, this large knob in the center.
This knob allows us to select energy in joules to deliver to a patient.
Once this machine is turned on you can rotate the knob to select the appropriate amount
of energy based on your patient's weight.
Other buttons that you will need to be familiar with a new in order to successfully deliver
a shock is the charge button.
You select the charge button once you have an appropriate voltage dialed in on that first
dial that we discussed and wait for the machine to give you a signal that it is charged.
The signal varies between machines.
In some machines it is an audio queue.
In some machines, for instance our machine, the shock button lights up once it is charged.
It is the responsibility of the person delivering the shock to ensure that everyone is clear
of the patient before shock is delivered.
That is because shock will be conducted through the patient and into any caregivers that are
still in contact with the patient.
The algorithm that we use here at Children's involves the person who's going to deliver
the shock saying, "I'm clear, you're clear, we're all clear," and then waiting for some
sort of affirmative before delivering that shock.
When the device is charged, the shock button is depressed once all caregivers are clear,
and the shock is delivered to the myocardium.
If you were called to the bedside when the patient was already in ventricular fibrillation,
and you did not have the pads conveniently placed the priority is to do whatever you
can to support the patient's cardiac output until you are in a position to defibrillate.
So that involves the immediate initiation of CPR.
Preparations for Defibrillation.
For an adult-sized patient, place the pads over the midsternum at the base of the heart
and the mid axillary line over the apex of the heart.
If you have a pediatric-sized patient, and/or the pads come into contact with each other
when placing both pads anteriorly you should use the anterior-posterior pad placement,
where one pad is placed anteriorly in the mid-sternal position, and the other pad is
placed posteriorly in the inter-scapular position.
In this video we will be following the American Heart Association Pediatric Advanced Life
Support, or Powell's Algorithm.
Please make sure to familiarize yourself with your locally used algorithm.
In PALS, the first defibrillation shock is given at 2 Joules per kilogram and the second
defibrillation shock is given at 4 Joules per kilogram.
Subsequent shocks may be given at 4 Joules per kilogram, or or some providers may increase
the dose of subsequent shocks to a maximum of 10 Joules per kilogram, or the maximum
adult dose recommended by a particular defibrillator.
Physiologically what you are trying to do is select the maximum amount of energy that
you need to defibrillate the patient without giving any more energy to the myocardium than
is absolutely necessary.
And that is because electric shocks delivered to the myocardium have the have the potential
to cause burns to the patient, like we have already discussed, they also have the potential
to cause localized myocardial damage.
And the amount of myocardial damage caused by the shock is proportionate to the shock
that is given: the more energy you impart to the heart, the greater amount of myocardial
damage you cause.
Finally, excessively large shocks significantly increase the likelihood or the risk of a post-shock
arrhythmia, which is something that you want to try to avoid.
Demonstration of Defibrillation: I am now going to walk you through an actual simulated
algorithm that makes the algorithm that we use here at Children's Hospital.
To orient you to the scenario, we have the device that we have just been discussing,
we have a read-out of the patient's vitals, lying here on the bed before me, I have a
10 kg infant who we have clinical worry of arrhythmias in.
And so I am going to place my pads to begin with.
I have chosen pads for ease of use.
Paddles would be equally acceptable.
So we have a patient in sinus rhythm with stable vital signs.
We have an acute change in the patient's rhythm.
It's a coarse baseline.
This is hemodynamically unstable rhythm.
We start by selecting voltage, 2 J/kg for the 10 kg infant.
We charge the device.
We say, "I'm clear, you're clear, we're all clear".
We discharge.
If the shock is unsuccessful, CPR should be performed for two minutes or five cycles.
After two minutes of CPR, the compressions should be paused while the cardiac rhythm
and pulses are assessed.
It was an unsuccessful shock.
The patient remains in a hemodynamically unstable ventricular fibrillation.
We effectively double the voltage that we're delivering by going to the 4J/kg mark.
We charge the device.
"I'm clear, you're clear, we're all clear."
We deliver our second shock.
If the shock is unsuccessful, CPR should be performed for two minutes, or five cycles.
According to PALS guidelines, if return to normal cardiac rhythm does not occur after
the second shock, epinephrine should be administered at this point, and then every 3-5 minutes
during the resuscitation.
After two minutes of CPR, compressions are paused while the cardiac rhythm and pulses
are assessed.
When a patient is not returning to a normal cardiac rhythm after 2-3 cycles of resuscitation,
remember to think about and correct causative factors that might make it difficult to convert
a patient's cardiac rhythm, including the H's and T's.
The H's include: hypovolemia, hypoxia, hydrogen ion (acidosis), hyper- and hypokalemia, hypoglycemia,
hypothermia.
The T's include: toxins, cardiac tamponade, tension pneumothorax, coronary or pulmonary
thrombosis, trauma.
Once again, an unsuccessful shock.
Once again, we charge the device at the same energy level.
"I'm clear, you're clear, we're all clear" and we deliver a shock.
If the shock is unsuccessful, CPR should be performed for two minutes, or five cycles.
According to PALS guidelines, if return to normal cardiac rhythm does not occur after
the third shock, anti-arrhythmics should also be considered at this point.
Amiodarone is recommended after the third shock, and then again after every other shock.
After two minutes of CPR, compressions are paused while the cardiac rhythm and pulses
are assessed.
And with our third shock we were successful in converting our patient back to a sinus
rhythm.
Even when you think you have restored the patient to what you recognize as sinus rhythm,
it is extremely important to immediately reassess the patient clinically.
Look at the blood pressure, look at the pulse, feel for both a peripheral and a central pulse
to ensure that this is a perfusing rhythm before you are reassured that you have definitively
converted the rhythm.
A point that I want to make using this patient and this weight is although you can dial in
voltages on the machine, the intervals are quite often not absolutely graded.
And what I mean by that is this is a 10 kilogram infant, and when we required our first shock
at 20 Joules it was very easy to selected a 20 Joule level because that exact number
appears on our graded voltage scale.
After our first shock was unsuccessful, when we needed a 4 Joule per kilogram shock there
is no setting for 40.
On this machine you can choose either 30 or 50.
If this is a choice you are forced to make, in selecting joules to deliver to your patient,
always round up.
So the second and third shocks that I delivered to this patient, I delivered at the 50 Joule
mark, which is a little bit over 2 Joule per kilogram.
So you round up, you never round down on that voltage.
Documentation.
The following should be documented in the patient's records: indication of the procedure,
date and time of the procedure, the number of shocks and the voltage required to defibrillate
the patient, duration of CPR, and the name, dosage, and route of administration for all
medications given during defibrillation.
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