IABP Mean Greater than Systolic?

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Hey all,

A question for people who are familiar with IABP. The other day, we had a patient on ECMO with a balloon, and the MAP on the balloon was reading higher than the systolic pressure on the balloon. Something like 67/47, mean was 74, Aug 100. We were talking with perfusion as most of us had never seen that before... and trying to figure out how that could happen. Does the balloon use the augmentation i.e. peak assisted systole for calculation of MAP? That was one of our possible explanations for this, however even after we had switched it to 1:2, unassisted MAP was still higher than unassisted systole.

Naturally, we re-zeroed, changed out console etc, with same results. So I started thinking a little deeper. I wish I could post a pic of the waveform, but this is an explanation of what it looked like. Systole, dicrotic notch, augmentation, then insted of normal drop to diastole, a small increase then decrease, sort of like a chair... was told it was a bicuspid waveform during diastole. So I understand this can be r/t inappropriate sizing or positioning as normally with the iabp, a significant amount of blood has been displaced which is why there is normally a steep decline after augmentation.... however if the balloon is inappropriately sized or position, more blood is left in the aorta during diastole resulting in that bicuspid waveform.

So normally, the monitor & balloon calculate arterial MAP based on it's on hemodynamic curve and everything underneath as opposed to the (SBP+2*DBP)/3, which is why your cuff BP does not equal your art BP even if the MAP is the same. Could that increased diastolic pressure (r/t bicuspid waveform) cause the balloon to calculate out the mean to be higher than the systolic?

Another possible explanation to that waveform other than inappropriate balloon sizing or incorrect position, the patient was on ECMO w/direct aortic art cannulation, so possibly high flows could alter the art waveform on the balloon?

If anyone has any expert opinions or explanations, it would be much appreciated. Trying to expand my knowledge here :) Thanks!

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Specializes in CVICU.

I cant say for sure as I dont have experience with ECMO but yes the augmentation pressure is accounted for in the MAP. I have seen the MAP > assisted systolic before with severe cardiogenic shock. The patient's own pulse pressure was so terribly low that the only good pressure being generated was from the augmentation pressure of the balloon. So assisted systolic/diastolic would have been something along the lines of 50/40 with the augmentation pressure of 100 and a MAP somewhere around 60 (just an approximate guess with the actual numbers).

So now that I'm thinking about it, why would one need a balloon pump while on ECMO? (no ecmo experience remember so forgive the basic question). Wouldnt the ECMO pump provide all the perfusion just as is the case while someones on bypass intraop? If I understand correctly the patients CO would be determined by the pump flows and whatnot and the MAP could be adjusted with pressors to maintain enough SVR for adequate organ perfusion while on ECMO/CBP. Is there something beneficial about the pulsation generated by the IABP? Thanks

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I cant say for sure as I dont have experience with ECMO but yes the augmentation pressure is accounted for in the MAP. I have seen the MAP > assisted systolic before with severe cardiogenic shock. The patient's own pulse pressure was so terribly low that the only good pressure being generated was from the augmentation pressure of the balloon. So assisted systolic/diastolic would have been something along the lines of 50/40 with the augmentation pressure of 100 and a MAP somewhere around 60 (just an approximate guess with the actual numbers).

So now that I'm thinking about it, why would one need a balloon pump while on ECMO? (no ecmo experience remember so forgive the basic question). Wouldnt the ECMO pump provide all the perfusion just as is the case while someones on bypass intraop? If I understand correctly the patients CO would be determined by the pump flows and whatnot and the MAP could be adjusted with pressors to maintain enough SVR for adequate organ perfusion while on ECMO/CBP. Is there something beneficial about the pulsation generated by the IABP? Thanks

Awesome thanks for that info, we weren't sure if the balloon actually counted the augmented pressure in it's mean calculation. As far as this particular pt, you're right, no need for the balloon with ecmo, but it was placed before they crashed this pt on ecmo, and we kept it in assuming he'd need it if we were going to attempt weaning off the ecmo in a few days. Plus, after talking with some of the perfusionists there is some benefit with coronary perfusion r/t counterpulsation since w/direct aortic cannulation the cannula sits above the root, and w/axillary comes in at the arch. Not sure if this is evidenced based or just case by case based.

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Specializes in CVICU.
Awesome thanks for that info, we weren't sure if the balloon actually counted the augmented pressure in it's mean calculation. As far as this particular pt, you're right, no need for the balloon with ecmo, but it was placed before they crashed this pt on ecmo, and we kept it in assuming he'd need it if we were going to attempt weaning off the ecmo in a few days. Plus, after talking with some of the perfusionists there is some benefit with coronary perfusion r/t counterpulsation since w/direct aortic cannulation the cannula sits above the root, and w/axillary comes in at the arch. Not sure if this is evidenced based or just case by case based.

The computer on the IABP console uses the augmented pressure to calculate the mean. As far as the IABP is concerned, the augmented pressure IS the diastolic. Looking at the mean pressure formula you can see that the diastolic pressure has much more influence on the MAP than the systolic. That is how the IABP is helpful in cardiogenic shock. You can have a pretty low systolic pressure, but combine that with a decent augmented pressure, you then have a decent MAP.

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Specializes in CTICU.

Sometimes pt is on IABP then decompensates and needs ECMO inserted. In that case they are anticoagulated for ECMO so you don't want to pull the balloon and risk bleeding. Plus some docs believe pulsatility is beneficial in a continuous flow system so they like to leave it with the ECMO.

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Sometimes pt is on IABP then decompensates and needs ECMO inserted. In that case they are anticoagulated for ECMO so you don't want to pull the balloon and risk bleeding. Plus some docs believe pulsatility is beneficial in a continuous flow system so they like to leave it with the ECMO.

I had my very first ECMO pt last week (yay!), and this was the exact scenario. Crashed pt onto ECMO when IABP and Impella failed. Took Impella out, but left IABP d/t risk of bleeding.

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Ghillbert,

I am new to the FNP program and noticed a thread on advanced path, if you still have study material and quizzes handy pls pls email or fax-thx a bunch Z

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