Published over 20 times, speaker at SMACCDub, Clinical Researcher for LUCAS, and more. David Halliwell is an experienced Paramedic, Managing Director of MDT Global Solutions, and Director for the Academy of Professional Development. You can find David on Twitter @sim_granny.
Dave Halliwell is presenting the Science of Resuscitation at a number of key events – EPICC Conference (Southampton), Dubai Ambulance Conference, and 'Spark of Life' in Adelaide.
This article was originally posted on David's LinkedIn page and is reposted with his permission.
This week I popped over to Paris to meet up with some of the key resuscitation opinion leaders from Europe, USA, Singapore, and the UK. The focus was to talk about the B-card – the Boussignac Cardiac Arrest System (I will explain more about this later), and to review the science of insufflation. The day started with the usual epidemiology and survival stats/human factors stuff, but then moved into science.
A couple of key messages from the day
"Insufflation is OK – it maintains O2 and cleverly removes CO2" – (I have played with this science previously, and agree... if its well designed!)
"Insufflation causes far less gastric distension than BVM – this is a good thing!" (200 ml vs 5000ml of intra-gastric gas over a 6 minute period). This had always been my concern, but study data was presented and backed with evidence based studies.
"Bag and Masks are a throwback to a time when we used the Bellows from the fire!" – Its true, people teaching resuscitation have often not focussed on the role of the lungs, but that is maybe about to change.
If you have seen my SMACC talk you will understand that the lungs are important, but on reflection I feel I had missed a bit...
The proposed change is not one towards a 30:2 IPPV type ventilator – but rather a system designed for treating the condition of "Cardiac Arrest" – continuous ventilation.
The case for rethinking
"Bag and mask ventilation causes reduced coronary perfusion." – Not good for the patient in cardiac arrest.
"Bag and mask ventilation causes reduced cardiac output." – Not good for the patient in cardiac arrest.
"Bag and mask ventilation causes gastric distension, splints the diaphragm and therefore reduces venous return and potentially therefore the capacity of the lungs... "
"Most people hyperventilate their patient when using a BVM." – There is a lot of evidence for this... This reduces venous return and destroys compression fraction.
"Bag and mask use causes a delay in chest compression and a subsequent drop in coronary perfusion flow." – Bad for a patient in cardiac arrest.
But incredibly, I sort of knew that stuff...
Then the team in France went on to discuss the reason for keeping 5cm H2O of pressure in the lungs: "After 10 mins or so, the airways and vessels in some patients may collapse (a common finding) but by adding a tiny amount of pressure into the lungs, the lungs (alveoli) and the vessels remain intact, and do not collapse! This allows for better perfusion and oxygenation and removal of CO2."
A eureka moment! Painful, but learning was now taking place...
Known as the "Pillow Effect", the team went on to explain that the reason we see blood coming up the ET tube in a cardiac arrest is most probably due to the fact that our CPR (and thus our elastic recoil of lung tissue) has been so effective at creating a thoracic vacuum that we have caused the collapse of the airways and vessels (reducing any gaseous exchange) and this is how we have subsequently caused damage to the lungs!
For the geeks amongst you I need to put the science in greater detail. Its going to take a few days to reference the studies etc...
I have seen the 'blood up the tube' phenomenon many times – but maybe never really understood it... I know I am not alone – I reviewed a few EMS sites and people talk about lung damage and suggest that they have caused Pneumothorax.
The lungs can be protected if we just keep the alveoli open! Gaseous exchange can take place, alveoli don't collapse, vessels don't collapse, blood can flow through the lungs.
A BVM will deliver 500 ml (if we are lucky) and will open the airways with positive pressure, but as we compress on the chest (or actively decompress) we push that air out of the airways with the first compressions and this is where the damage is occurring to the alveoli.
Every compression is forcing blood and air out of the lungs, and every decompression is creating a vacuum and sucking the alveoli and small vessels closed.
It's always great to challenge our thinking and to learn something new, but this one was painful. As LUCAS came to the fore in early 2004 we were using Boussignac tubes and seeing far less occurrence of blood from the ET tube, we just didn't understand why.
The 'Pillow Effect' in detail
"Collapsed alveoli are very difficult to re-open and restore ventilation to. Thus, it is necessary to keep them inflated at the end of exhalation by maintaining some positive pressure in the airways." (Acosta et al, 2007).
So what is B-card? – If you are familiar with the concept of insufflation, with B-card you are essentially attaching a face mask over the patients face (tightly) which is attached to an O2 cylinder set at 15 lpm. This creates sufficient alveolar pressure to keep the airways from collapsing during chest compression and acts therefore in a protective manner. The team showed that at 5cm H2O pressure, venous return was not affected, and gastric distension was far less than BVM. Called the 'Pillow Effect', the cushion of air inside the alveoli is seen as sufficient to protect the lungs from the force of the chest compression.
Using the science developed by Dr Boussignac and the Vygon team, the O2 is naturally at higher pressure in the airway than in the blood stream and so the O2 passes into the blood whilst the CO2 is removed through the change in intrathoracic pressure caused by chest compression
There are RCT's underway and I will try and post a few more of the important other thoughts. The trip this week was useful – a chance to rethink the ventilation and chest compression conundrum and spend time with people who challenge the traditional ways of thinking.
The Science of B-card resuscitation will be presented at a number of key resuscitation events in the UK and overseas this year.
I am left wondering again about the effect that adrenaline has upon alveolar blood flow...
Thanks to the team at Vygon and the many presenters who shared their research, and for putting together a group of open minded individuals.
I have no links to Vygon and aim to merely present the discussion in the hope that others can comment and think...