Matt,
Thanks for your comments.
The first question that I feel needs answering (accepting that survival is
clearly the most important outcome measure) is that acceptable levels of
oxygenation are achievable when compared to conventional single rescuer BVM
CPR. Standardising this will clearly be a challenge.
It occurs that some of this data might be usefully obtained from
irretrievable resuscitation scenarios with blood gas analysis with
conventional compared with AED continuous chest compressions.
The reason for emphasising the importance of oxygenation is the hope that
the neurological outcome for survivors will not be compromised by such an
approach.
John Black
Oxford
-----Original Message-----
From: Dunn Matthew Dr. (RJC) ACCIDENbtainabT & EMERGENCY - SwarkHosp-TR
[mailto:[log in to unmask]]
Sent: 28 February 2003 15:28
To: [log in to unmask]
Subject: Re: Active compression/decompression devices for CPR.
> For some time I have wondered whether an alternative approach that may
> result in more effective CPR in the unintubated in such
> circumstances might
> be:
>
> 1. Nasal (x2 if possible) + oral airway
>
> 2. High flow O2 delivered via well fitting Hudson mask
>
> 3. Continuous chest compressions administered with ACD device
This seems a sensible approach. Despite the amount that has been written on
different ways of ventilation in CPR there is not a lot of evidence. Kern
KB. Cardiopulmonary resuscitation without ventilation. Crit Care Med. 2000
Nov;28(11 Suppl):N186-9 summarises much of the work done on ventilation
during cardiac arrest (admittedly much of it looking at his own papers). The
interesting thing is that ventilation does not appear to improve outcome
(and there have been a couple of animal studies suggesting that standard
forms of ventilation may worsen outcome).
Hence, in a single rescuer situation, anything that makes ventilation less
of an issue is likely to be useful even if tidal volumes etc are lower.
I think the advantage of this approach compared to the thumper is that one
would assume that in a low output situation, positive intrathoracic pressure
(as provided by the thumper and by positive pressure ventilation) is likely
to reduce capillary flow.
> Getting ethical approval to develop the evidence base for
> such an approach
> would be a challenge but such an approach might be of benefit for such
> patients.
>
Depends on how you'd intend to study it. It certainly has got harder to get
approval for RCTs in patients unable to consent. However, a well presented
proposal for a good quality RCT of adequate size looking at an appropriate
endpoint and coming from someone with a track record would probably get
approval. Basically, I can't see RECs being all that happy with a study that
just looks at ROSC or cardiac output rather than return to life in a study
without consent- although different RECs look at it differently.
I'd point out though that the problem here is not that RECs are difficult,
it's that producing a worthwhile study is difficult and RECs (at least
theoretically) won't approve a study that's not worthwhile.
So, numbers. Anyone got any proper data? If not, extrapolating from my own
data: per 100k population per year you've got 100 cardiac arrests (including
in hospital and out of hospital), maybe 5- 10 survivors to discharge; but if
you exclude VF arrests responding to the first few shocks (i.e. CPR with kit
not an issue unless you get the kit there before the defib, which ethics
committees won't like) and children, this cuts that to maybe 2-3 per 100k.
Assuming a 10% improvement in outcome (i.e. 2.75% rather than 2.5%
survivors) and a Beta of 0.8, this works out to a sample size of around
2,500 patients so with a population of 5 million, even allowing for 50% non
compliance with protocol you could get your data in a year. Afraid that's
the numbers you need to get a worthwhile study. If you got London or West
Mids ambulance service on board it might be possible.
Matt Dunn
Warwick
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