Breathing during cardiac arrest

[dbooksta]

I've been wondering whether self-breathing can be used as an indicator of effective CPR.

I've been told that people don't continue breathing after effective heart function stops because the diaphragm quickly runs out of oxygen. Is this correct?

Or, during a heart failure, is there some other effect that impairs breathing? I suspect it's the latter, since otherwise CPR would never include respiration, and effective CPR would be evidenced by a subject beginning to self-breathe. But I'm curious to know the actual physiology relating breathing to cardiac function.

 

[SpecialK]

It is not uncommon for pts in cardiac arrest to have agonal breathing. This is not a marker of effective CPR, something like ETCO2 is.

With very good CPR it has been reported in the literature for pts to have some movement; although not exaggerated; but I have heard of people giving some rocuronium if it becomes contextually "significant".

 

[cprted]

Like Special K said, agonal resps can be common in an arrest, especially in a fresh arrest. Give this video a watch, you'll see the agonal resps. Don't confuse this state with breathing, the patient is not breathing, they are in cardiac arrest.

In one case, I had a pt make a few agonal resps after DCing CPR follow a 40 minute code ... interesting to see, but I wouldn't use the presence or absence of agonal resps as a measure of good CPR.

Regarding respiratory control, here are a good set of videos
https://www.khanacademy.org/science...athing-control-ir/v/peripheral-chemoreceptors

The entire Health and Medicine library at Khan Academy is worth browsing, lots of good content there. https://www.khanacademy.org/science/health-and-medicine

One final note, do watch your terminology. "Heart failure" is a specific disease and is not the same as cardiac arrest. Just like heart attack and cardiac arrest are not the same thing.

 

[dbooksta]

Thanks, and I apologize for any butchered terminology. It sounds like you're repeating something that is well-known (but above my level of training): "Don't confuse [agonal respiration] with breathing, the patient is not breathing, they are in cardiac arrest." I.e., it sounds like you're saying that respiratory arrest always accompanies cardiac arrest. If that is true, why is it?

Or let me pose my question more carefully: Suppose one has a patient with no detectable pulse. They may be suffering asystole or various flavors of fibrillation, due to numerous causes well above my pay grade. Suffice it to say that their heart is not circulating blood. From the time their pulse stops how long are they expected to breathe, and what ultimately stops normal breathing? My understanding is that the subconscious breathing cycle is driven by very basic brain-stem chemistry. Therefore, as long as the brain stem is alive is it not calling for breath? Or is it calling, but the diaphragm really burns through its blood's store of oxygen in -- what, one breath? Three? (Well again, I'm pretty sure I'm thinking down the wrong pathway, because if it was a matter of oxygen then CPR would start breathing absent some separate cause inhibiting it.)

 

[NomadicMedic]

If a patient has no palpable pulse they will stop breathing by the time you've finished that pulse check (if they weren't already apneic already)

And what stops breathing? Cardiac death. The agonal breaths are the brains literal "last gasps" trying to get some oxygen.

The heart may beat for a short time when the patient is in respiratory arrest, but not vIce versa.

 

[cprted]

Without blood flow, the tissues of the brain cease to function normally. The first symptom of this is typically loss of consciousness. What I think you're asking is, 'if good CPR restores circulation to the brain, why doesn't the brain start functioning normally again (ie, breathing on its own)?' In some cases, it can--to a point, but it is rare. There are stories out there of cardiac arrest patients becoming slightly combative during CPR, but it isn't common. The reality is that by the time we get to them, the brain tissue has been without circulation for some time and there is damage to the tissues. So after they've been down for a few minutes, giving the brain some blood flow isn't enough to immediately restore normal function.

Anecdotally, I've been on two calls for cardiac arrest where on my arrival, the patient was a GCS 15. Both of these cases involved witnessed collapse with immediate bystander CPR and rapid deployment of an AED by bystanders and in both cases the AED had delivered 2 shocks. These patients had a rapid return to normal function due to the short period of time their brains were without circulation.

As well, even the best CPR typically only produces about 20-30% of normal cardiac output. While this can help ward off serious long term neurological problems, 20% of normal blood flow doesn't allow the brain the function as it normally would. When you get ROSC however and the patient's cardiac output starts to return to something that resembles normal, this is where in some cases we will see the patient start to make a respiratory effort, perhaps some purposeful movement of the limbs, response to painful stimuli, etc.

 

[dbooksta]

Thank you again -- that's very informative!

Part of my erroneous assumption was that the brain stem would continue functioning until death, which is on the order of minutes. It sounds like the reality is that even the stem begins to go "unconscious" as quickly as the higher-level brain -- i.e., on the order of seconds after oxygen deprivation.