Question 19 from the first paper of 2007
There is a surprising lack of sensible evidence behind the routine process of cardiopulmonary resuscitation.
But, it would be absurd to expect high-quality randomised controlled trials in this area. For instance, how would one randomise people to the non-CPR group? Thus much of what we do is a combination of physiology, instinct, and animal studies.
What we don't know about cardiopulmonary resuscitation
- We have no idea as to what rate of compressions there should be. We suspect it would be around 100, because any greater rate than this causes resuscitator fatigue (its hard work!) whereas a lower rate is associated with a poorer outcome.
- We don't know what the depth of compressions should be, or whether the depth correlates well with ventricular chamber compression. However, the deeper you go the more likely you are to have a successful defibrillation.
- We don't know what the ideal respiratory rate should be during a cardiac arrest, but we suspect it is lower than normal (because the arrested patient is producing less CO2, given that large swathes of tissue are using anaerobic metabolism). The ILCOR people have settled on a 30:2 ratio irrespective of the number of rescuers; this was arrived at not necessarily by science, but by convenience (in order to simplify teaching and skills retention).
- We don't know whether compression-only CPR is any good. It has been said that (at least initially) the gas mixing which occurs in the chest during cardiac compressions is sufficient for the exchange of gas during an arrest, and that any extra breaths on top of this gas mixing is unnecessary. However, no studies of this exist. Additionally, I suppose that the patients who have arrested due to hypoxia would probably benefit from additional respiratory support.
- We don't know whether ALS in general is actually beneficial. Apart from defibrillation, there is no evidence that advanced life support actually influences clinically meaningful outcomes.
- We don't know if the drugs help. In actual fact, there is no evidence that any drugs use during CPR actually improve survival to discharge from hospital (again, the ILCOR guidelines say as much)
What we DO know about cardiopulmonary resuscitation
- We know that defibrillation is critical, and should be performed as soon as possible. The best chances you have are within the first 3 minutes.
- We know that after the restoration of electrical activity, cardiac output is still poor. CPR should continue for 2 minutes after each shock attempt.
- We know that there is no imperative to intubate the patient. The ILCOR people have repeatedly written that there is no evidence to recommend one airway management technique over another. However, if you are going to have any sort of airway, few would argue that the gold standard is an endotracheal tube.
- We think there might be some benefit to amiodarone in shock-refractory VF; or rather, it seems slightly better than placebo. In the group of arrested patients being CPRed by ambulance officers, the use of amiodarone for "refractory" shock-resistant VF resulted in a slight (10% ARR) improvement in their chances of surviving the ambulance ride. Thats right, no talk of survival to discharge whatsoever.
The ultimate destination should be the cath lab
With the notable exception of all those Hs and Ts which are unrelated to myocardial ischaemia, we must acknowledge that the majority of cardiac arrests are due to cardiac events, and most cardiac events are due to something amenable to percutaneous intervention. Ergo, these people should all undergo angiography at the nearest convenience. Indeed, the odds ratio of improved survival in these people is about 5 according to one enthusiastic study.