best review thus far with excellent pictures
Extra-corporeal Membrane Oxygenation (ECMO)
Review from the NEJM (NEJM 2011;365(20):1905)
If you bypass lung entirely, it has no way to get CO2 becomes alkalotic and may infarct
If V/A then heart must pump against the pressure gradient introduced into the aorta
You know when there is no native CO because there will be a straight arterial pressure tracing just showing a mean pressure
Pulmonary pressure from a hyperdynamic right heart will overcome hypoxic vasoconstriction
Oxygen is flow dependant
Muscle/kidney/Liver clear lactate
ECMO works by sending blood through artificial lung either membrane or hollow fiber. Blood flows counter-current to gas
Rated flow of a membrane is how much blood can be raised from 75% to 95% O2 sat in a given time
Maintain Activated clotting time of 180-200
Study of crash bypass for cpr-nonresponsive cardiac arrest (Inten Care Med 2007;33:758)
CESAR trial shows cost effectiveness for transfer to ECMO center if severe resp fx (Lancet 2009;
When you put a person on cardiopulmonary bypass despite being on full
> cardiopulmonary bypass defined as diversion of all systemic venous
> return to the oxygenator, there is sufficient amount of noncoronary
> collateral and other flow to the heart which will fill the heart (for
> eg bronchial flow etc). This will normally be ejected by the heart and
> the left ventricle will be kept empty. Now if the heart is asystolic
> or fibrillating it cannot kick out this volume into the aorta and so
> the heart will now distend and as per Laplaces law with increasing
> radius there will be increasing wall tesnions (to put it in simplistic
> terms it becomes increasingly difficult to distend a baloon as it
> enlarges and the wall tension will be higher) . This implies that
> wall tesnion wll increase and with increasing distention the wall
> tension will increase and thus decrease progressive subendocardial
> perfusion and at one stage there will be no subendocardial myocardial
> perfusion , a condition which is practically worse while not
> externally visible. This distention is negated by ‘venting” ie a
> placing another cannula or catheter to collect this excessive return
> and divertting it away from the left ventricle , be it by direct
> incision on the ventricle (less often used today ) or by indirect
> methods ranging from the aorta to the pulmonary artery (based on the
> fact that it is a valveless circuit after the pulmonary valve).(I can
> go on further (as this is a very important topic in CPB
> pathophysiology) but to make a long story short – you need to have the
> heart empty and beating for it to function well. If it cannot beat
> prevent it from distending by approproate venting. At times we
> actually have to squeeze the heart and empty it and prevent
> distention. A term which is we refer to as “Theri haath me Jagannath”
> meaning (roughly translated that “the Lord is in your Hands” to
> emphasize that the lfie of the patient depends on you preventing
> distention (and actually is a vulgar joke (( you could get it 
))
> Prasanna
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