EMCrit 267 – They are not All Right!! An interview on Hemodynamic Assessment with Mike Patterson

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Michael Patterson FCICM FANZCA

Mike is an intensivist anaesthetist in Melbourne. He has spent years thinking about disasters seen in anaesthetics and ICU--most of them are hemodynamic ones. His original interest in this problem stemmed from the death of a young lady having elective gynae surgery, in the setting of anaphylaxis. She had an easily palpable central pulse and reassuring EtCO2 throughout. He was involved late due to issues with arterial access. She died of a hypoxic brain injury solely because her pressure was too low for too long. He has been reflecting on this over the last few years and building up a picture of the problems and the solutions. Subsequently, he had been involved in one patient that died in the setting of a POCUS pulse but inadequate pressure and another young lady who lived despite nearly the same problem occurring as the lady that died.

Central pulses are almost meaningless

- We are mostly just feeling a change in pressure

- Hence 50/10 might feel similar to 120/80

Central pulses are particularly dangerous in distributive shock where the pulse will be felt strongly below 50/-. This has been my repeated experience. It is easily palpable even in hypovolaemic shock with BP < 60 on occasion - You can’t measure pressure from a central pulse until you place an arterial line

POCUS Pulse as a Representation of Adequate Pulse

The use of POCUS to confirm flow in the femoral artery or palpation of a femoral artery pulse is problematic, as you discussed. In your hands (and proper resuscitationists), there will be an arterial line in place very quickly so it is a non-issue. Obviously, those involved in resuscitation should fix their system to achieve this but for lots of reasons that is a problem in many parts of the world (including most Melbourne ED’s/ICU’s).

The problems with ROSC in the setting of PEA or profound hypotension in general are:

POCUS pulse has the same problems as a central pulse unless applied to the brachial artery where you can place a manual cuff and visualize the occlusion pressure

Normal EtCO2

A normal EtCO2 is not reassuring that the pressure is adequate, as you mention - It is useful to suggest ROSC when it kicks up - It is dangerous as any reassurance in distributive shock where pulmonary perfusion is maintained and EtCO2 often doesn’t drop at all despite BP’s < 50/- - In the cardiac arrest setting, PaCO2 has often risen significantly so an EtCO2 in the 30’s may still represent inadequate perfusion let alone pressure I like your step-wise summary of the progression to ROSC. It is brilliant.

The yellow zone is where all the badness is happening in the anaesthetic world and I wonder if that is true in ED and ICU but we just don’t recognize it (as the patients are sick beforehand so any bad outcome isn’t attributed to the haemodynamic management).

You explained the problems with this zone excellently but I wonder if people will appreciate the dangers of a POCUS pulse or a palpable central pulse for that matter. I am concerned they will be misused and prolong periods of hypotension. I know you were only talking PEA but the issues are the same in profound hypotension.

My approach is as follows in the setting of profound hypotension = POCUS pulse:

Radial Pulse?

Identify that the radial pulse is rapidly and easily felt before you have a problem - This is obviously irrelevant for those presenting in cardiac arrest - In most other circumstances, if you knew it was strong and easily palpable prior, you can’t end up with confirmation bias - convincing yourself there is no problem. Occasionally it is difficult to locate prior,