Questions About CPR

[docB]

We all do (or at least supervise) CPR every day but I have some questions about where we are now in terms of the data. There have been papers saying that chest compressions alone are just as good as doing CPR. Is that because it's as good or is it because more people are willing to do compressions without mouth to mouth? Is all the data behind the AHA guidelines of doing 2 minutes of "quality CPR" without checking a pulse, with the hope up bringing up cororary artery pressure, based on outcome data or just lab data?

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[Apollyon]

I was told when the 2 minutes of good CPR idea came out that the 2 minutes arrived because no healthy volunteer could do 4 minutes, so they pared it down.

 

[gutonc]

Another really great question. Have things gotten so slow in Vegas that you have time to get all academical now? Between this and the DKA thread you're running a virtual Grand Rounds here.

I have no idea what the answer to your question is but I would posit the somewhat pedantic devil's advocate view that it doesn't really matter to "us" in the hospital setting.

Single rescuer CPR, which is what the "compressions only" method is aimed at the lay audience, trained in BLS only who finds someone down. In that setting, I think good chest compressions beats bad chest compressions + bad breaths every time and is only designed to temporize until an AED or paramedic arrives.

In the EMS or in-hospital code setting, you'll usually have >1 person to run the code (making compressions only moot) and you're basically just killing time until somebody gets the pads, epi and tube ready anyway and you can get on with the "better living through chemistry/electricity" part of your day.

Having said all that, I hope somebody does come up with a less snarky and more helpful answer than mine because it's a great question and brings up an important point, that many people don't question the science/data behind new guidelines, just read them and run.

 

[docB]

Another really great question. Have things gotten so slow in Vegas that you have time to get all academical now? Between this and the DKA thread you're running a virtual Grand Rounds here.

It actually came to mind when I realized I have a leacture to give my paramedic students in a few weeks.

 

[EC3]

It's my understanding that in a cardiac arrest there is enough oxygen in the blood to sustain viable perfusion so long as circulation is maintained. This does not hold true, though, if the primary reason for arrest is from a respiratory etiology.

 

[Dwindlin]

It's my understanding that in a cardiac arrest there is enough oxygen in the blood to sustain viable perfusion so long as circulation is maintained. This does not hold true, though, if the primary reason for arrest is from a respiratory etiology.

This was the rational I was given last time I recertified.

 

[eriedoc514]

as we all know, the most important aspect of any full arrest is "high-quality" CPR with early defib. That being said there has been some outcome based literature to address your question. Cant remember the name of the trial, but it was out of europe some where. Basically what it said, was that there was similar one year survival rates in patient who received standard 30-2 cycles prehospital (prior to ALS arrival) and those who received compressions only (until ALS got there).

That being said, there was a similar study which looked at 2 min of CPR prior to AED, and just AED without CPR, and the results of that, showed a higher survival rate in the group which received the CPR prior to AED. This study did not offer a rationale as to why, but i would imagine that it has something to do with shoking a full heart, with coronaries that have oxygenated blood in them, as compared to not.

probably not the best answer in the world, but hope it helps.

 

[Jeff698]

My understanding is that the one variable of CPR that makes the biggest difference time and again is the number of 'quality' compressions/minutes. Quality, in this case, being depth.

Interruptions in compressions, for whatever reason, loose the pressure gradient that has been developed with those compressions. It takes a bit to reestablish that gradient, during which time there is inadequate blood flow.

Since oxygenation initially isn't the problem and poor circulation is, compression only seems to be what makes a difference (early defib not being a part of this discussion and assumed to still be highly important).

If I stumbled upon someone without all of my toys, I'd do compression only. Even with my toys I have my techs do uninterrupted compressions during the early phase of resuscitation. I'll intubate with compressions ongoing (another reason I love the bougie) or have them stopped for the briefest time possible if I must.

Take care,
Jeff

 

[MSTigER]

I could see two reasons why the use of respirations is not as important as maintaining circulation: a) how much oxygen content is actually in our exhaled air? especially with our now increased cardiac output and b) in order for efficient perfusion of O2 across the alveolar-capillary interface, we need active blood flow to create a gradient and continually pull oxygen across. The way I see it we are putting suboptimal O2 concentrations into a basically "shunted" environment.

 

[pseudoknot]

The compression only CPR idea is supported both by animal data and also by field data (real outcomes on real live, sort of, patients). Most of the studies in the US on this seem to come out of Arizona. I don't have references right now and have the OB shelf on Friday, but I think in a pretty recent Annals of EM that group published something about CPR with no ventilation being superior. Check it out, and maybe look for their references.

As for the guy above talking about CPR buying time until intubation, drugs, and defibrillation, only one third of that was right (defib). There's actually a randomized trial in the new JAMA from Europe finding no benefit to epi.

 

[gutonc]

As for the guy above talking about CPR buying time until intubation, drugs, and defibrillation, only one third of that was right (defib). There's actually a randomized trial in the new JAMA from Europe finding no benefit to epi.

Yeah...but I posted that before that issue got to my house. So it's still cool. When they take Epi out of ACLS, I'll take it back.

 

[BADMD]

I could see two reasons why the use of respirations is not as important as maintaining circulation: a) how much oxygen content is actually in our exhaled air? especially with our now increased cardiac output and b) in order for efficient perfusion of O2 across the alveolar-capillary interface, we need active blood flow to create a gradient and continually pull oxygen across. The way I see it we are putting suboptimal O2 concentrations into a basically "shunted" environment.

The third reason is more subtle. Every time a breath is given, the intrathoracic pressure is increased, decreasing venous return and negatively impacting the coronary perfusion pressure. Every delivered breath actually sets you back from trying to reach 15 mmHg.

 

[pianoman511]

as we all know, the most important aspect of any full arrest is "high-quality" CPR with early defib. That being said there has been some outcome based literature to address your question. Cant remember the name of the trial, but it was out of europe some where. Basically what it said, was that there was similar one year survival rates in patient who received standard 30-2 cycles prehospital (prior to ALS arrival) and those who received compressions only (until ALS got there).

That being said, there was a similar study which looked at 2 min of CPR prior to AED, and just AED without CPR, and the results of that, showed a higher survival rate in the group which received the CPR prior to AED. This study did not offer a rationale as to why, but i would imagine that it has something to do with shoking a full heart, with coronaries that have oxygenated blood in them, as compared to not.

probably not the best answer in the world, but hope it helps.

I believe there was a pig-based study showing that the coronary perfusion pressure drops off a lot with any interruption in compressions (i think it may have been part of the study involving the ITD - impedance threshold device).

The 2 minutes of CPR rule was actually part of the protocol (for an unwitnessed arrest) where I used to work (EMS) and the rationale was similar to the above. The idea is that with the 2 minutes of CPR you build up the coronary perfusion pressure which also, in a v-fib arrest, makes the v-fib more coarse and increases the chances of a successful conversion with the first shock.

 

[leviathan]

You can look at the problems from two angles, both from lay rescuer and ACLS-trained providers:

Lay-rescuers:
-Lower fraction of time performing compressions (and thus a worse CPP) when constantly switching back and forth
-Poor compressions and over-aggressive ventilations when constantly switching back and forth in a 30:2 (or whatever ratio) fashion
-In general a hesitance to do any CPR when the concept of ventilations are involved

ACLS (with someone always at the head and someone always at the chest)
-When not intubated, a decreased chest compression fraction
-When intubated, a decrease in venous return, preload, cardiac output, and CPP due to ventilations, especially by overzealous and aggressive rescuers

There was just a study released by my old medical director relating survival to discharge and the fraction of time compressions were performed. I don't think it reached a P<0.05 though. http://emergency-medicine.jwatch.org/cgi/content/full/2009/1030/1

While in arrest your VO2 is quite low and thus you can be sustained for quite some time with your existing arterial oxygen content. By the time you've been down long enough to require ventilations, you probably have no chance of survival anyhow. I wonder if continuous compressions will be the future for even in-hospital arrests.

 

[leviathan]

Another interesting study I saw the other day showed an example of ECG progression of a patient from an extremely fine vfib into a very coarse vfib after 2 minutes of good CPR. Pretty cool stuff...

 

[Doctor Bob]

I believe there was a pig-based study showing that the coronary perfusion pressure drops off a lot with any interruption in compressions...

Blehh... who did they get to do mouth-to-mouth on the pigs between compressions for the control group?