Once you start CPR, you wanna really make it count.
Because patients are much more likely to survive if you perform high quality CPR
than if you perform poor quality CPR.
And there are five major determinants of CPR quality
which we're gonna discuss in some detail.
The first is the rate of compressions.
100 to 120 is the rate that every rescuer should be aiming for.
Two, is adequate compression depth.
We wanna go about two to 2.5 inches or 4 to 5 centimeters.
Three, is continuity.
You should be performing CPR
for a minimum of 60% of your total resuscitation time if not more.
Fourth, is chest wall recoil.
That’s diastole in cardiac arrest
and that’s what allows the heart to refill
so we wanna make sure that we allow the chest to recoil
so the heart can fill normally making each compression count.
And last, is hyperventilation.
Hyperinflating the lungs, decreases cardiac output
and is another variable that produces adverse outcomes in cardiac arrest.
So, let’s start with compression rate.
There have been a number of studies looking at rate
and this is one example.
In this study they looked at the mean rate of chest compressions
among a large sample of cardiac arrest patients
and they found that the patients who had compressions
at a rate of roughly a 100 to 120 had the highest probability of ROSC
which stands for return of spontaneous circulation.
And they also have the highest probability of survival to hospital discharge
or having a longer term positive outcome.
So a 100 to 120 is the rate you wanna go for
and there's actual science showing us
that patients are more likely to survive when we use that rate.
Compression depth, we have a similar study looking at depth as an isolated variable.
Again, for patients getting return of spontaneous circulation back,
the optimal compression depth was just under 5 cm.
And same thing for survival to hospital discharge,
the optimal compression depth was just a little bit over 5 cm.
And what they found in general is that any compression depth
over about 4 cm or 38 mm produce an odds ratio of 1.910 of survival to hospital discharge.
Meaning, that if you have compressions of greater than 38 mm across the board,
you're twice as likely to survive.
So it's a really important variable and a really easy one to optimize.
This graph is about chest compression fraction.
So in this study they look at the percentage of time in the overall cardiac arrest
that the patient had active chest compressions being performed.
And they stratified according to the percentage.
So 0 to 20, 20 to 40, 40 to 60, etc.
And they found not surprisingly,
a linear increase in the likelihood of return of spontaneous circulation
as the chest compression fraction increase.
So if you spend more time during the code performing CPR
you're gonna to get a better outcome and a higher probability of survival.
This is the same data, but this is actually a survival curve
rather than the group stratified data
and once again chest compression fraction of 0.8, 0.9 or 80% to 90% at the time
produce the highest likelihood of return of spontaneous circulation.
In another study looking at chest compression fraction,
the outcomes were a little bit different.
In this study, they found that actually a 60 to 80% chest compression fraction
produce the highest odds ratio of survival to hospital discharge
and that’s what the current guideline recommends.
So you wanna be at a minimum of 60% ideally closer to the 80% range
for your chest compression fraction.
The bottom-line though, is you're clearly never gonna know numerically
what your fraction is during the course of a resuscitation.
You just wanna make sure that your CPR is as continuous
and as uninterrupted as you can possibly make it.
So chest wall recoil is a physiologically important variable
but there's actually no human studies on it that demonstrate improved survival
because it’s a kind of a difficult phenomenon to study.
But basically the idea is if you lean on the chest in between compressions,
you're gonna increase the patient’s intrathoracic pressure, right?
You're smashing down on the chest
so that's gonna raise the intrathoracic pressure.
Well, we all know that positive pressure ventilation
also raises the intrathoracic pressure.
So if you cram more air into the lungs
you're gonna raise the thoracic pressure.
And the bottom-line, what brings blood back into the heart during diastole?
It's negative intrathoracic pressure, right?
It's that negative pressure gradient
that pulls blood from the periphery back up to the heart.
So if you raise the intrathoracic pressure and make it not negative,
you're gonna prevent the heart from filling
and you're gonna decrease your cardiac output
by decreasing your stroke volume.
The ultimate effect?
Again, is gonna be impaired cardiac output
and that means less blood flow to the heart itself,
less blood flow to the brain,
and less likelihood of spontaneous circulation.
So bottom-line, high-quality CPR is what you need to do
to optimize your chances of survival
and the determinants once again are:
push hard, 4 to 5 cm;
push fast, a 100 to 120 compressions per minute;
keep it going, you wanna make sure your chest compression fraction is a minimum of 60%
if not more during the course of the arrest
and avoid hyperventilation and chest wall leaning.
If you do those five things you're gonna increase your patient’s odds of survival.