Understanding IABP values

[Catticus11]

My hospital uses the Maquet IABP in our cardiac critical care units.

For those who are not familiar with the system, it's format includes the ECG and it's trigger, the BP per fiber optic cable, the map, and then the Augmentation pressures. If the IABP is not in a 1:1, the unaugmented pressures are listed below the augmented pressures.

Our education for the IABP says that BP will be low since that's the expected outcome of an IABP, and to monitor MAP per the IABP system. BP will also be low due to the fiber optic cable placement in sorta, and that's a lower pressure area compared to a radial arterial pressure.

However, one of the hospitalists told me that the reason the BP appears low is because they aren't a true systolic and diastolic BP since the fiber optic is reading the highest pressure as the systolic and that highest pressure is Augmentation, and the Augmentation value on the screen is the most accurate for use of a SBP value.

Where I got confused is how the SBP value differed from the Augmentation value on our monitor since Augmentation is usually higher than the SBP. And thus, how is the SBP being determined?

And also, more importantly, how should I be administering medications? Based off the BP per the IABP, or off the Augmentation pressures.

If you need to explain it like I'm a child, then please, by all means...

[PresG33]

You have it backwards. The augmentation pressure is the diastolic. When the heart pumps, the balloon DEFLATES and basically causes a vacuum that decreases after load and minimally increases cardiac output. At the end of systole (when the aortic valve closes) the balloon inflates to push blood backwards into the coronaries to perfuse them (remember the heart is perfused during diastole). A properly timed IABP will have an artificially high DBP because of the back pressure and an artificially low SBP because of the effect of balloon deflation. Therefore you have two options: get a radial arterial line to see what the perfusion is at the end of the vascular tree, or use the MAP on the IABP because this is a better guide of what the organs are seeing in terms of pressure.

[nurserobinson281988]

We use the mean BP on the IABP pump. I have seen residents/ fellows put in BP parameters based off of Augmentation, but I quickly call the staff Cardiologist to have this changed to the mean (mean was in the upper 40s-50s and pt had signs of hypo perfusion)Poster above explained that fantastically, so I will save you from the repetition.

[Catticus11]

Just to clarify, are the numbers on the IABP machine reading the artifically high DBP as the SBP? And the artificially low SBP as the diastolic?

[nurserobinson281988]

No, the IABP is not flipping them. The IABP is measuring the BP more centrally in the body (in the aorta. In critically ill people systolic BP is higher and diastolic bp is lower in the radial artery than in the aorta. inversely, aortic SBP is lower and diastolic bp is higher in the aorta than the radial artery. Since you would normally have a bp reading from a more peripheral location such as the radial artery, that is part of the reason for the lower blood pressures. The other reason is described by the previous poster. But systolic is still systolic and diastolic is still diastolic bp.

[nurserobinson281988]

Intra-art SBP amplification mech

Check out this page on distal pulse amplification!

[PresG33]

As the other poster said, the machine is just reading the assisted SBP as lower because it is. It reads the high DBP as the augmentation value. The best way to visualize the difference is to set the balloon to 1:2. This way you will be able to compare the assisted and unassisted SBP and DBP. You will see that the balloon will make the SBP lower than the normal SBP, followed by the augmentation at the dictotic notch that will be higher than the SBP, then the end diastolic that will be lower than the regular DBP. If these don't happen then either the balloon is bottomed right or the pt doesn't need an aloof because it's not really doing what it's supposed to.

[ghillbert, MSN, NP]

The IABP is reading correctly. If however you used a NIBP cuff for a BP reading in a patient with 1:1 IABP, yes it would read the augmented diastole as "systolic" bc it's the highest number in the cycle.