Apnoeic Oxygenation in Resuscitation: Is it time?

We are finally seeing the years of airway in resuscitation dogma being challenged. The original approach to airway which mandated intubation and probably led to significant delays in CPR and an increase in mortality, are now gone.

Bag-valve-mask vs supraglottic vs intubation

The literature that compares intubation, laryngeal mask(LMA) and bag valve mask(BVM) has given us a definite answer to which active airway device is best. Patients with in-hospital cardiac arrests, were found to have a worsened neurological outcome if they were intubated within the first 15 minutes of resuscitation(1). Prospective studies looking at out-of-hospital cardiac arrest, found that intubation did not confer any benefit over BVM or supraglottic airway(SG)(2,3). The most recent AIRWAY-2 trial, a prospective randomised trial, reconfirmed this(4).

Passive ventilation during cardiac arrest

The original cardiocerebral studies(5), where there was no active airway intervention for the first few minutes of CPR ( ie., 3 x 200 compressions), only passive airway, demonstrated significant increases in survival and more specifically, in neurologically intact survivors. This has led to questioning the use of positive pressure ventilation delivered by BVM or via LMA or definitive endotracheal airway. The theory here, is that positive pressure ventilation results in increased intrathoracic pressure which leads to decreased coronary perfusion pressure.

The use of passive ventilation or BVM ventilation and minimally interrupted continuous cardiac compressions has already been adopted by emergency medical services. Here the initial airway management is by passive ventilation or BVM ventilation(6)

It was found that patients where the initial rhythms were pulseless VF/VT receiving minimally interrupted cardiac compressions and being treated with passive ventilation (non-rebreather masks), were more likely to survive to hospital discharge than those receiving BVM ventilation(38.2% vs 25.8%)(7).

In these studies passive ventilation was used only in the initial stages of the resuscitation ie., the first few minutes. What would be the effect of using passive ventilation throughout the whole resuscitation period?

We know that the PaCO2 and the PaO2 do not change dramatically in the first few minutes of resuscitation(8). We also know that continuous flow ventilation during mechanical compressions(ie., compression/decompression CPR), provides adequate ventilation(9), however compression only CPR is ineffective in generating tidal volumes adequate for gas exchange, because these volumes are not greater than the dead space(10).

Can we use apnoea oxygenation with a nasal cannula?

It is important to understand the mechanism by which apnoeic oxygenation works. It results from a net removal of 240ml/min of gas from the alveoli, resulting in negative alveolar barometric pressure. The mechanism of movement is bulk flow down a pressure gradient. It is only effective following adequate pre-oxygenation, to maintain the oxygen reservoir and the pressure gradient.

Theoretically, in a patient in cardiac arrest, where response is rapid and active and compression/decompression CPR is used, apnoeic oxygenation should be adequate. We need to talk the following into consideration:

1. The passive ventilation studies have for the most used this technique in the initial stages of resuscitation. We need more work to look at the effect when used for the whole resuscitation period.
2. There must be active compression/decompression used
3. We need to ensure that we maximise oxygenation to replenish the functional residual capacity.

Where are we now? My approach?

There are already systems in play using passive ventilation and generating good ventilation. The Boussignac cardiac arrest resuscitation device is one device that (11) allows continuous insufflation of oxygen, creating an initial static pressure of 4-5cm H2O. It creates a virtual valve resulting in a positive intrathoracic pressure during thoracic compression and a negative pressure during decompression. It has been shown to be successful during resuscitation.

I believe in putting a high flow nasal cannula on every patient immediately during the resuscitation. We know that in most cases the cause in the adult patient will be VF/VT. I would also add a non-rebreather and perform continuous cardiac compression for 3 cycles of 200 compressions. Following this the nasal cannula would remain and the patient would be ventilated with BVM, unless there was active compression/decompression. At this point I would even consider an LMA with directed passive ventilation through this.

This may be the next big thing. Watch this space.

References

1. Wilt J et al. Intubation During In-Hospital Cardiac Arrest. JAMA. 2017;317(19):2019.
2. Hasegawa K et al. Association of Prehospital Advanced Airway Management With Neurologic Outcome and Survival in Patients With Out-of-Hospital Cardiac Arrest. JAMA. 2013;309(3):257-266.
3. Wang H et al. Effect of a Strategy of Initial Laryngeal Tube Insertion vs Endotracheal Intubation on 72-Hour Survival in Adults With Out-of-Hospital Cardiac ArrestA Randomized Clinical Trial. JAMA. 2018;320(8):769-778.
4. Benger J et al. Effect of a Strategy of a Supraglottic Airway Device vs Tracheal Intubation During Out-of-Hospital Cardiac Arrest on Functional OutcomeThe AIRWAYS-2 Randomized Clinical Trial. JAMA. 2018;320(8):779-791.
5. Ewy G. A new approach for out-of-hospital CPR: a bold step forward. Resuscitation. 2003;58:271-272.
6. Bobrow BJ et al. Minially interrupted cardiac resuscitation by emergency medical service for out-of-hospital cardiac arrest. JAMA 2008:299;1158-1165.
7. Borrow BJ et al. Passive oxygen insufflation is superior to Bag-Valve-Mask ventilation for witnessed Ventricular Fibrillation out of hospital cardiac Arrest. Annals of EM 2009:54(5);656-662
8. Strand M et al. Arterial Blood gas changes during cardiac arrest and cardiopulmonary resuscitation combined with passive oxygenation/ventilation: A METI HPS study. J Int Med Research 2018:46(11);4605-4616.
9.  Steen S et al. Continuous intratracheal insufflation of oxygen improves the efficacy of mechanical chest compressions-active decompression CPR. Resuscitation 2004;62:219-222.
10. Deakin DD et al. Does compression only cardiopulmonary resuscitation generate adequate passive ventilation during cardiac arrest? Resuscitation 2007:75;53-59
11. Moore JC et al. Evaluation of the Boussignac Cardiac arrest device (B-card) during cardiopulmonary resuscitation in an animal model. Resuscitation. 2017 Oct;119:81-88

Peter Kas