This article arose from a discussion at my workplace surrounding the use of passive oxygenation during the initial stages of cardiac arrest. It was suggested that we would not be using this technique until it becomes a North American or specifically a Canadian standard of care.
I suspect that what was meant by the term “Standard of Care” referred to the current guidelines for Emergency Cardiovascular Care as set out by the American Heart Association and the Heart and Stroke Foundation of Canada. For interest’s sake, an article on the legal definition of standard of care can be found here.
So let’s look first at what the current guidelines say about passive oxygenation.
Some EMS systems have studied the use of passive oxygen flow during chest compressions without positive-pressure ventilation, an option known as passive oxygen administration.
220.127.116.11 2015 Evidence Summary
Two studies compared positive-pressure ventilation through an endotracheal tube to continuous delivery of oxygen or air directly into the trachea after intubation by using a modified endotracheal tube that had microcannulas inserted into its inner wall. A third study compared bag-mask ventilation to high-flow oxygen delivery by nonrebreather face mask after oropharyngeal airway insertion as part of a resuscitation bundle that also included uninterrupted preshock and postshock chest compressions and early epinephrine administration.69 Continuous tracheal delivery of oxygen or air through the modified endotracheal tube was associated with lower arterial PCO2 but no additional improvement in ROSC, hospital admission, or ICU discharge when compared with positive-pressure ventilation. High-flow oxygen delivery via a face mask with an oropharyngeal airway as part of a resuscitation bundle was associated with improved survival with favorable neurologic outcome. This study, however, included only victims who had witnessed arrest from VF or pulseless ventricular tachycardia (pVT).
18.104.22.168 2015 Recommendations – New
We do not recommend the routine use of passive ventilation techniques during conventional CPR for adults. (Class IIb, LOE C-LD) However, in EMS systems that use bundles of care involving continuous chest compressions, the use of passive ventilation techniques may be considered as part of that bundle. (Class IIb, LOE C-LD)
Okay, so what is the big deal with passive oxygenation? Why would we bother? We were all taught in BLS courses that one rescuer does compressions and the second rescuer applies the defibrillator and ventilates the patient using a BVM. But is this the best and most effective method of resuscitation.
In his article titled “Continuous Chest Compressions vs. 30:2. Does it Matter? Depends on the quality?”[i], Tom Bouthillet refers to compression only CPR for the first 4 to 6 minutes of a cardiac arrest, delivered by bystanders, as being a good thing. He references a paper by Dr. Gordon Ewy[ii] which discusses the benefits of uninterrupted chest compressions for out of hospital witnessed V-fib cardiac arrest. Mr. Bouthillet also discusses the importance of not over ventilating a patient, and the need for high quality chest compressions. But does this mean we should eliminate Positive Pressure Ventilations? The answer is not really clear.
Here is a scenario which would represent a typical rural EMS response to a cardiac arrest in Manitoba. The call comes in to the 911 centre. While the appropriate EMS crew is being dispatched, the call taker will be instructing the caller on doing compression only CPR. Now I cannot speak to all areas of Manitoba, but where I work, our time from dispatch to being at the patient’s side can be anywhere from 5 minutes to well over 60 minutes. As a rule, as soon as we are sent to a cardiac arrest, we have asked for a second ambulance to respond as well.
When we do arrive, if we are lucky, there is someone doing CPR. But there are only two paramedics initially on scene. The second truck may be 5 minutes away or 55 minutes away. Here is where I am going to suggest that passive oxygenation would be a properly utilized procedure. My partner immediately assesses the patient, confirms lack of pulse and breathing, as well as lack of obvious signs of death, and initiates high quality chest compressions. Because we cannot verify that the compressions done prior to our arrival were done properly, we would typically do a two minute cycle of compressions before a rhythm analysis. So during this time, my job would be to insert an OPA, or possibly and iGel airway, and apply oxygen via nasal cannula or using the O2 port on the iGel, and deliver passive oxygenation to the patient, at 5 to 10 litres per minute. Then I would apply the defibrillator pads, pre-charge the defibrillator, and at the appropriate time, analyze the rhythm and deliver a shock if required. We would then switch roles, and I would immediately continue with chest compressions. My partner could then obtain vascular access for drug and fluid administration. If, during this time, the second ambulance arrives, we would have enough team members that one person would be assigned to manage the airway and ventilations, and Positive Pressure Ventilations would begin. If note, then once an IV or IO has been established, the two responders could then manage compressions, ventilations, defibrillation and drug/fluid administration, although I believe this is something that would have to be practiced repeatedly to become an effective team.
Now let’s take a step back and explore how passive oxygen delivery works. Rather than recreate the wheel here, I am going to offer a quote from the article titled “No Desat”[iii] by Dr. Rich Levitan, who is recognized as expert in airway management. In his article, Dr. Levitan is talking about apneic oxygenation prior to and during the process of placing an endotracheal tube. So here is what he says regarding the passive delivery of oxygen via a nasal cannula.
After the induction of apnea, nasal cannula diffuses oxygen down the trachea to the alveolus. It is absorbed across the alveolar capillary membrane, despite the absence of respiratory movements, even as laryngoscopy is being performed. This occurs because of the difference in gas production and uptake in the alveolus, and the differences in the solubility of oxygen and carbon dioxide in the blood. Carbon dioxide excretion into the alveolus diminishes during apnea because carbon dioxide is approximately 25 times more soluble than oxygen in blood. It is estimated that during apnea CO2 is excreted into the alveolus at only 10 ml/min. Conversely, oxygen is absorbed at 250 ml/min. The resultant negative pressure gradient (-240 ml/min) creates a sub-atmospheric pressure in the alveolus. The net result is that during apnea, oxygen insufflated into the upper airway will be “drawn” down the trachea and into the alveolus. Oxygenation can be maintained in non-breathing humans for 100 minutes through apneic diffusion, even as carbon dioxide builds up in the blood.
Okay, so that’s the science behind it. Now, should we be using it? In the scenario I described above, I believe that the use of passive oxygenation would be helpful due to the limited resources in terms of available team members. If there are enough responders, than most definitely have one person assigned to airway and ventilation. Just to muddy the waters a bit more, if you are sure that the etiology of the arrest is respiratory in nature, airway and oxygenation becomes more important. And having made that statement, the science still shows that we cannot maintain adequate coronary perfusion pressure when we continually interrupt compressions.
So where does that leave us. Passive oxygenation is another tool we can use in the appropriate setting if it would benefit the overall resuscitation effort. But there still needs to be more random controlled trials to prove an overall benefit to the patient. There are a number of EMS services which incorporate passive oxygenation into their resuscitation protocols at the appropriate time. This topic remains a lively conversation in the resuscitation community, and perhaps we will see more studies and new information before the next change in the Emergency Cardiovascular Care guidelines, which should be released for 2020.
As always, your comments are welcome. Thanks for visiting the EMS Soapbox.
Passive oxygen insufflation is superior to bag-valve-mask ventilation for witnessed ventricular fibrillation out-of-hospital cardiac arrest. Bobrow BJ1, Ewy GA, Clark L, Chikani V, Berg RA, Sanders AB, Vadeboncoeur TF, Hilwig RW, Kern KB.
Oxygenation, Ventilation, and Airway Management in Out-of-Hospital Cardiac Arrest: A Review Tomas Henlin, Pavel Michalek, Tomas Tyll, John D. Hinds, Milos Dobias
[ii] Ewy G. (2004). Cardiocerebral Resuscitation The New Cardiopulmonary Resuscitation. Circulation. 2005;111:2134-2142. Retreived from http://circ.ahajournals.org/