Nick Barrett, Head of ECMO at GSTT gives us an update on advanced respiratory support
Nick starts with a quick summary of the evidence: mortality is improving, a wealth of techniques are available, the data shows we often don’t use them, there’s a link between driving pressure and mortality.
Fantastic 3D imaging of lungs under mild, moderate and severe ARDS. A standard 420ml tidal volume doesn’t account for the true available alveolar volume in these three levels of disease. Severe ARDS patients have 280ml effective lung volume, so 420ml is well over 100%. The consequence is further damage due to our ventilation strategy.
Everyone loves a schematic of an ECMO circuit! Nick makes it sound simple.
What’s the evidence?
CESAR has been widely criticised but it does suggest a survival benefit if a patient is referred to a specialist centre.
The retrospective H1N1 data again suggests a survival benefit.
In fact, if a patient with single organ respiratory failure is referred for ECMO has receives it, their survival probability is 95%!!
Survival can be predicted by the PRESERVE score (Schmidt 2013 ICM 39:1704).
Indications for referral
- Reversible ARDS
- Murray Score > 3
- < 7 days ventilation
- No major life limiting co-morbidity
- No contraindication to anticoagulation
- VV Cannulation
- Diagnosis – Nick emphasises that ARDS is not the diagnosis. Have they got viral / bacterial pneumonia or an interstitial pneumonitis?
So how hard can it be? Nick emphasises the importance of good equipment: stiffened wires using fluoroscopic guidance and proper dilators with a 5cm tapered tip.
Nick explains the physiology of shunt during VV ECMO. Since cardiac output is often much greater than pump flow, there will be a shunt and subsequent low SpO2. This can be optimised by tweaking cardiac output: neuromuscular blockade or even beta-blockers.
Rest the lungs: PEEP ~10cmH2O, driving pressure ~5cmH2O, tidal volumes ~50ml.
One indication for an Echocardiogram: does the patient have a heart! Nick points out how easy it should be to obtain an echo given the latest mobile technology.
Everyone gets CT (“vertex to anus”), bronchoscopy (infection and cytology), echo and blood tests (autoimmune and vasculititic screen).
At this end of the spectrum, a CXR adds nothing so the patients need CT imaging.
Ouch! 1 in 8 patients who get ECMO have intracranial haemorrhages. But, 1 in 12 patients who don’t get ECMO but are similarly sick also have intracranial haemorrhages. Why is this – sepsis, CO2 effect?? Nick doesn’t know.
Line infections are rare. The line are in the groin and are medium-long term, but they’ve only had 3 infections in 7 years!
Importantly, you don’t need lungs to play on a computer game or even mobilise. Impressive video from Nick, but it looks like 8 staff are supporting this mobile patient!
Survival is good and stable over the last 6 years. Survival at 6 months around 70%.
What about those that are referred but only advice was required: survival is 94%. And those that get refused… 21%.
A short presentation of VA ECMO to support acute cardiomyopathy. The room stirs when Nick shows us an PLAX echo with very little ventricular movement.