Cardiogenic shock and Frank Starling

#KYJ - Cardiogenic Shock

Let’s unpack this common type of shock we see in our clinical deteriorating patient’s.

I edit, proof and English polish nursing and paramedic assignments as a side service to my seminar and cruise boat education sessions.

In many recent case studies, pathophysiology is a common theme that needs a bit of work to schmooze the passing paper in to an A Grade masterpiece.   The last 3 months was full of shock, and especially cardiogenic, so I thought I’d dedicate this episode of #KnowingYourJargon (KYJ) to this topic.

Let’s commence with nomenclature.  Cardio = heart.  Genic = to originate/create (think Genesis as the book of creation from Old Testament Judeo/Christian and Islam mythology) .

Shock- is fundamentally a state of imbalance between cellular oxygen demand vs delivery of oxygen to cells .   In a nutshell, shock is “relative global cellular hypoxia” (Timmings 2004) 

Then cardiogenic shock therefore means :

Global cellular hypoxia that originated from heart failure.

To unpack this further we need to understand heart pumping function, and it’s discourse- heart failure.

Given the adult heart pumps blood; the volume it pumps measured over a minute is termed Cardiac output.  Normally this equates to 4.2-7 litres/min which is pretty awesome given its size.

Now when there is injury, or death of heart muscle, or  degenerative changes occur with lifestyle challenges and the encroachment of the autumn years; the efficiency of the heart as a pump wanes.

This is called heart failure and can occur in with left or right heart or both, termed congestive heart failure (CHF)

These slow changes over years are called “chronic” , but after a cardiac event such as a myocardial infarction (commonly termed heart attack), or a traumatic injury to the heart eg stabbing, or blunt crushing trauma, then the cardiac failure is called Acute.  Irrespective of aetiology, a heart in failure wont pump adequate oxygenated blood around the body to meet the demand of cells-  this is shock. Cardiogenic shock.

Now read on if you are interested in diving deeper.

This is where you and I get our geeky on!!

Frank -Starling Mechanism(Law)

Otto Frank and Ernest Starling were a couple of turn of the century early 1900s geekoids that had a hankering for the dynamics of the heart pumping function- Otto loved playing with frogs, and Ernest was a Dog man, so armed with their work on Frogs n Dogs, they went and got a whole mechanism named after themselves.

Essentially what they asserted was two monumental principles.

First that a heart needs to fill up with blood before it can pump out any blood . . .

Yep, I know- crickets...

Their second assertion is that not only does the heart need to fill up with blood, but it’s chambers must actually be stretched a little to get a good strong elastic contraction.

I know these seem obvious, but in the world of medicine and cardiology especially, that fill up the heart till it’s a bit stretched like a balloon part is called “Preload”. You have to have preload the ventricles before an output from the pump will be efficient.

Think of a rubber band .

It’s elastic potential is only realised when you stretch it, and heart muscle is the same.  If you don’t pull back on a rubber band you can’t ‘feeyonnnng’ (real word*) it across the room at your loved one.

*ok that was t a real word- but you get it hey?   Stretch The rubber and whoosh there is a release of tension.

In cardiac ventricles this preload works like a partially inflated balloon.   Let it go and the elasticity causes the air you blew into the balloon to propel it across the room.

Hearts need to fill with blood and preload.

Now Frank and Starling also said that too much stretch (preload) is going to work against the pump.  Preload is a good thing but overload causes failure .

Like Tim Tams- some = good , but the whole packet = bad.

In heart failure the pump has lost its inotropy (force of contraction) so if the weak muscle can’t pump the reservoir of blood out efficiently= cardiogenic shock happens.

Likewise in MIs, or acute muscle injury.

A secondary mechanism is the hypoxia of heart muscles itself.  Muscle needs oxygen to pump (contract) but also to relax and fill.   So ischaemic (hypoxic) hearts are stiff and non compliant-  remember Starlings first principle ?   Heart has to fill up with blood first.

Well in stiff poorly filled hearts, output will drop.

Again - cardiogenic shock.

Are we done?

Credit: Robert Timmings 

#ECT4Health 

@ECT4Health 

#RobTimmings

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