tet spells and knee-chest position

[Faisal Vali]

Can someone please explain to me why the knee-chest position helps when dealing with tet spells in
cyanotic tetralogy of fallot patients?

What I've been told is that it tends to increase systemic resistance - thus decreasing the R->L
septal shunt, and encouraging pulmonary flow.

I guess I don't see the physiology behind the knee-chest position increasing the systemic
resistance?

(Does it increase venous return? Is it some form of reflex that triggers vasoconstriction? Is it
increasing intrathoracic pressure (but that would decrease venous return) and thus increasing
arterial tone similar to the mech behing valsalva?)

thanks in advance! regards, Faisal Vali

 

[Terrence Chun]

Faisal Vali <[email protected]> wrote in
news:[email protected]:

> Can someone please explain to me why the knee-chest position helps when dealing with tet spells in
> cyanotic tetralogy of fallot patients?
>
> What I've been told is that it tends to increase systemic resistance - thus decreasing the R->L
> septal shunt, and encouraging pulmonary flow.
>
> I guess I don't see the physiology behind the knee-chest position increasing the systemic
> resistance?

You and pretty much any one else who has stopped to ponder that question.

If you ask any pediatric cardiologist, they will give the stock answer that you mentioned: "Increase
systemic vascular resistance, decrease infundibular spasm, increase pulmonary blood flow."

All of the therapies for tet spells functionally do those things, but their efficacy is mostly
anecdotal; nobody is very academic when a kid's saturations are 30%. I have actually performed
transesophageal echocardiography on patients during a hypercyanotic spell during induction of
anesthesia (a common time for having spells) and did not see any "spasm".

My $0.02.

- TC, md Pediatric cardiology and electrophysiology