Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

Why doesn’t CPR work for trauma

In Potentially Reversible Causes of Cardiac Arrest and the Futility of CPR for Trauma Arrest, I did not really explain, Why doesn’t CPR (CardioPulmonary Circulation) work for trauma?

So I asked myself How might someone, who is bad at drawing, demonstrate this? With bad drawings. Feast your eyes on these.

The heart is more complicated than a ball of blood, but for the purposes of explanation, a ball of blood is as complicated as the heart needs to be. In these diagrams, the ball of blood is the left ventricle.

Yes, the blood from the pulmonary veins is red, so that is in red. The time when the mitral valve is closed and the aortic valve is open, is what matters for compressions. Compressing a pulseless heart should create this condition.

As long as there is blood in the heart, it should flow in one direction during compressions.

By squeezing the bag of blood heart, an effective compression should produce some sort of circulation.

When there is no blood to squeeze out of the heart, there is no circulation.

An additional problem with CPR on the exsanguinated patient (patient who bled out) is that the heart is probably still beating. The purpose of CPR is to provide a poor substitute for real heart beats. If the heart is still beating, the poor substitute is not going to do a better job of moving the blood that is not there.

When the patient is pulseless due to blood loss –

The heart is probably still beating.

The heart rate is probably a lot faster than 100 – the poor substitute rate of chest compressions.

The problem is not a lack of cardiac activity.

What about tension pneumothorax?

The problem with tension pneumothorax is that the mediastinum is shifted to one side, or compressed, to the point that the major blood vessels are badly kinked. As with a straw that is kinked, nothing flows through a badly kinked blood vessel.

Compressing harder, or faster, or both, will not make any difference. The only way to improve cardiac output is not by compressions, but by decompression. This is why the patients in need of needle decompression will be losing their vital signs.

As with bleeding out, this pulseless patient’s heart should still be beating more effectively than anything any chest compression could produce. The heart just can’t push the blood through the kinked blood vessels – and neither can chest compressions. No circulation = no pulse, even though the heart is beating well.

What about cardiac tamponade?

A cardiac tamponade is similar to a tension pneumothorax. In stead of air leaking into the pleural space and preventing the expansion of the lung, there is blood leaking into the pericardial space and preventing the expansion of the heart. The heart and the lungs need to expand and contract to work. The pleural space and the pericardial space are not supposed to contain air or blood.

After each heartbeat, the heart needs to expand to allow blood back in for the next heartbeat.

If the heart cannot expand, it cannot effectively contract.

If the heart cannot expand, due to already being compressed by a huge hematoma in its lining, then compressing that heart will not improve the cardiac output. Again, the heart is beating, just not well enough because it cannot expand. Adding compressions will not improve anything.

Late entry – 14:30 on 11/17/2011 –
As Jon Levine explains in the comments –

Nice commentary on the futility of CPR in trauma (hypovolemic) but to be more accurate you should show the tension pnuewmothorax causes blockage/kinking of the preload not afterload to be be more accurate and repersentaive of the poor cardiac output ” Nothing into the pump nothing out.”

This is true. The blockage on the input (the more flexible/less rigid blood vessels) is more accurate than blockage on the output. This is something to help understand what is going on with a tension pneumothorax.

In the comments, Windy City Medic also provides an great explanation of the way that man made pumps fail in the same way that the heart fails. Link to comment

Anoxia is one exception to this, but it is easy to determine if there is any reason to use CPR. If appropriately done compressions do produce a pulse, then the potentially reversible cause of cardiac arrest is not exsanguination or obstruction.

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Comments

  1. Excellent explanation for anyone who didn’t fully understand your original post.

    • Windy City Medic,

      Thank you, but a video would make it much more clear.

      People seem to have a mental block with the concept of a heart beating, but not producing a pulse.

      .

      • I always call the heart a pump. As with any pump, either lack of liquid to be pumped, or obstruction in the lines of the pump, will make it so the pump won’t pump. It will work, it will run, it will maybe even pump, but nothing’s getting anywhere.

        A fuel pump in a car will run as long as there’s a power source, but if there’s no fuel in the tank, then it’s not really doing anything, the engine will not run because it doesn’t have fuel, and eventually the pump will burn out. If there’s a kink in the fuel line, the fuel pump will pump fuel, but the fuel won’t go anywhere because it can’t get past the obstruction. Cranking up the pump won’t do any good, it will only make the fuel pump work harder and burn out faster.

        A water pump in a well will run as long as there’s a power source, but if there’s no water in the well, then it’s not really doing anything, the people at the top will stay thirsty because there’s no water, and eventually the pump will burn out. If there’s a kink in the water lines, the water pump will pump water, but the water can’t go anywhere because it can’t get past the obstruction. Cranking the pump won’t do any good, it will only make the pump work harder and burn out faster.

        A heart in a body will beat as long as it’s properly oxygenated and fed, but if there’s no blood in the body, then it’s not really doing anything, the body will start to die because it doesn’t have blood (oxygen and nutrients) and eventually the heart will burn out. If there’s a kink in one of the blood vessels (or a thrombus/embolus, etc.) the heart will pump blood, but the blood can’t go anywhere because it can’t get past the obstruction. Cranking the heart (with drugs or by doing chest compressions) won’t do any good, it will only make the heart work harder and burn out faster.

  2. you know some1 needs to make a halfway decent movie bout this! woulda helped me a ton going through combat lifesaving courses! and woulda helped me save my buddy in the field!

    • C.L.S.,

      you know some1 needs to make a halfway decent movie bout this! woulda helped me a ton going through combat lifesaving courses! and woulda helped me save my buddy in the field!

      In EMS, and all of medicine, we do a poor job of explaining to students what they should understand. We think that, because we understand it as we explain it, they should understand it as they hear it.

      I am divorced, so I am well aware that what I say is not always interpreted the way I intended. Similarly, there are a lot of people in EMS who jump to conclusions about what I mean without asking for any clarification. We assume that there is one obvious way that something can be intended and we ignore all other possibilities. Maybe this is why we have been so aggressive in testing by means of multiple choice tests.

      We justify this with the explanation – there is one and only one best answer. A fraud, but as long as we are just trying to prepare people to treat life threatening conditions, why worry about reality?

      There is a video, at least one, of a heart beating without producing a pulse, but I cannot remember where I saw it. It had the feel of EMRAP.TV or Keeping Up with Emergency Medicine, but I have not been able to find it at either site. It includes an ultrasound of the heart beating with no blood in it. If anyone knows where I can find this, I would love to include a link to it.

      Sorry about your buddy. Combat medicine is improving dramatically. We view the military as opposed to innovation, but they are actually the source of tremendous innovation. Putting one’s life on the line would seem to decrease the fear of being yelled at by a doctor for not blindly following a protocol. Dr. Jeffrey Cain does some excellent presentations for EMS on this. He wrote a part of the JEMS War on Trauma special supplement. PDF Download of the entire supplement.

      .

  3. Those are some very seriously improved illustrating skills you’ve demonstrated in providing this explanation. MS Paint?

  4. Nice commentary on the futility of CPR in trauma (hypovolemic) but to be more accurate you should show the tension pnuewmothorax causes blockage/kinking of the preload not afterload to be be more accurate and repersentaive of the poor cardiac output ” Nothing into the pump nothing out.”

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