Clinical Pearl 76: Ventilation Strategies in Cardiac Arrest

You have a patient in cardiac arrest who needs some sort of ventilation or oxygenation strategy.  Three choices exist:

1. 1Passive Oxygenation
2. Asynchronous Ventilation
3. Ventilation with interposed intermittent compression

Which do you choose?  First we should acknowledge a few things before we look at the science.

1.      For the noncardiac arrest patient, passive oxygenation is a great thing for patients who are breathing at least 4 times per minute and saturation is at least 93 percent.  If the patient is below these numbers you should bag until you get to these numbers and then go back to passive oxygenation (NRB with High-Flow Nasal Cannula or BVM with Peep Valve and High Flow Nasal Cannula Underneath WITHOUT squeezing the BVM or CPAP). For three minutes if the decision to intubate has been made

2.      CC-CPR (chest compression CPR is a great thing) for “Untrained Rescuers.”  When a layperson arrives at the scene the benefit of good compressions outweighs stopping compressions to ventilate.  This practice is proven in multiple studies.

3.      Bagging people can cause harm.  It decreases myocardial blood flow,  decreases cerebral blood flow, causes shunting by distending the alveoli and opens the Lower Esophageal Sphincter which results in gastric distention and aspiration from vomiting.  Additionally this makes it harder to intubate patients.

So now the science. .. First we should acknowledge that not breathing is a bad thing so if we are not going to ventilate cardiac arrest patients based on the science we better make absolutely sure the science is very very overwhelming for not ventilating.   This is because not ventilating/breathing results in increased PCO2, decreased oxygenation and leads to anoxic brain injury/brain death.  In lieu of great science (published papers) we need many expert societies to back us up that we are doing the correct thing. 

Luckily, this is one of the less controversial topics for us because we really only have one paper that the current recommendation is based on. ..that is correct one paper on what to do when EMTs or higher medical personnel oxygenate/ventilation in cardiac arrest.   The 2015 AHA guideline states “for witnessed cardiac arrest in a shockable rhythm, it may be reasonable for EMS systems with priority-based multi-tiered response to delay positive-pressure ventilation by using a strategy of up to three cycles of 200 continuous compressions with passive oxygenation insufflation and airway adjuncts”  was based on an older paper in 2009 by Dr. Bobrow which appeared in Annals of Emergency Medicine.  No further research research supports this position. 

Now guidelines are somewhat silly because by the time they come out more science exists or they are already outdateed because of a lack of other published articles.  Before we look at the sole paper this was based on, we should be clear what it states:

1. This practice may be reasonable which is hardly an endorsement
2. It is only for Witnessed cardiac arrests.  If you are doing this based on unwitnessed cardiac arrests…it is dangerous and not based on any science or recommendation furthermore and you are risking harm.
3.  It is only for initial shockable rhythms.  So if the initial rhythm is not VFIB or Pulseless VT, (or the AED fires)..there is no science or recommendation for any society and you are risking doing harm.

More importantly…lets look at this paper that this recommendation is based on……..a subgroup analysis of 200 patients.  In this subgroup analysis, patients who received up to 3 cycles of 200 compressions had better neurologically intact survival only in the witnessed group.  30 compressions is 18 seconds so 200 compressions is 120 seconds.  Therefore if you are doing passive oxygenation for more than 200 compressions (120 seconds), this is against the guideline as well.  So why was the recommendation only in Witnessed VF/Pulseless VT?  It is because all the other patients did WORSE when they got passive oxygenation.  Specifically:

1. Neurolocally Intact Survival in the Unwitnessed Cardiac Arrest group was  better in BVM group 13.8% vs 7.3%.  That is correct the chance of Neurologically intact survival was two times greater in the group who were bagged if they had an unwitnessed cardiac arrest.  If you are doing passive oxygenation in this group you are decreasing someones chance of neurologically intact survival.
2. Neurologically Intact Survival in nonshockable rhythms was better with BVM 3.7 vs. 1.3.  So you in this study three times more patients had neurologically intact survival if they had a BVM used vs. Passive oxygenation.  Again if you are doing passive oxygenation in this group you are decreasing someone change of survival!!!

So why did the one group do better when they had passive oxygenation…the answer may be very simple.  The study did not keep track of how fast EMS ventilated.  In studies you can show differences in two study groups by either the treatment group doing very good or the control group doing very bad.  It is quite possible since we know that excessive bagging is bad that patients in this study  were bagged too aggressively and that is why there was a difference between the intervention and control group.  The other major explanation is that patients who had witness cardiac arrests  required minimal need for ventilation since they were just breathing.  Remember they only did passive oxygenation for 2 minutes then they bagged them too!

Since there is really no evidence for this practice…are there any studies which demonstrate we should not be doing this?   The Annals of Emergency Medicine paper and current recommendation say we should not be doing this in unwittnessed arrests or nonshockable rhythms or greater 200 compressions.  Moreover all of the papers that show benefit and make recommendations for CC-CPR are for “untrained rescuers.” However all of the studies done with this were observational studies.  Finally a large EMS prehospital cardiac arrest trial was published in New England Journal of Medicine by Nichol in December 2015.  This major trial of 114 EMS agencies, 23,711 adult patients was done by the Resusciation Outcomes Consortium and actually supported complete ventilation!!!  It was statistically very superior to everything done and reinforced that some complete ventilations are necessary.  While its primary endpoint evaluation continuous compressions vs interrupted and found better outcomes with interrupted it showed that complete ventilation was better than asynchronous.  Although this study had a few problems…. it is the overwhelming the most well done study ever on the topic…  Finally in the last major review published by M. Chang April 2017 titled “The Past, Present and Future of Ventilation During CPR” in Current  Opinion in Critical Care Medicine discusses that ventilations of 8-10 are the best methods for cardiac arrest patients.   This author agrees!!!

Conclusions:

1. Based on one older and small paper, passive oxygenation for Witness Cardiac Arrests with Ventricular Fibrillation/Pulseless Ventricular Tachycardia (AED shockable rhythm) is not unreasonable however better literature suggests that even this practice is not best evidence.
2. Prolonged passive oxygenation by medical personal (greater than 200 compressions) has no evidence to support it and potentially can cause harm.
3. Passive oxygenation by medical personal for unwitnessed cardiac arrests or nonshockable rhythms is not supported in the literature and potentially can cause harm.