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IABP Review

http://www.nurse411.com/Review_Sheets/IABP_Review.html

Increase O2 Supply / Decrease O2 Demand
NTG (coronary artery vasodilation) / NTG (peripheral vasodilation)
More oxygen delivery / Beta-blockers
PTCA / ACE inhibitors
CABG
IABP Inflation / IABP Deflation

Table 1 – Ways to effect the myocardial O2 supply and demand balance

Mechanics of IABP:

Inflation occurs just before the dicrotic notch (when the aortic valve closes). This is when the coronary arteries fill. If we increase the pressure in the aorta at this time, then the pressure of blood going into the coronary arteries will also increase, and in turn increase coronary artery perfusion. Since balloon inflation does not force blood only to the coronary arteries, additional benefits of balloon inflation are increased perfusion to the carotid arteries above the balloon (cerebral perfusion), and increased perfusion to the renal arteries below (maintaining renal blood flow and function). Thus we have increased O2 supply to the heart, brains and kidneys.

Deflation of the balloon occurs just prior to or just after the aortic valve opens (during systole when the ventricles are contracting). This is when blood is ejected from the ventricles into the aorta. By deflating the balloon at this time, we create a “vacuum effect” which lowers the pressure in the aorta. More blood is then ejected from the left ventricle to fill the void in the aorta created by the balloon deflation. Therefore, with the same effort, the ventricle has become more efficient. The heart pumps more blood per contraction, without needing more oxygen. Thus, we have decreased the O2 demand of the heart muscle.

So, by the inflation and deflation we have decreased the O2 demand at the same time increasing the O2 supply. Frequently this will correct the O2 imbalance and stabilize the patient’s hemodynamics.

Balloon inflation should occur about 40 milliseconds before the dicrotic notch forming a sharp “V” shape on waveform. If inflation is timed correctly Rule #4 (below) will be true. If inflation is timed late then Rule #4 will be violated

Balloon deflation should occur just before systole. If timed right Rule #3 (below) will be true, if timed incorrectly Rule #3 will be violated.

Figure 1 - Intra-Aortic Balloon pump arterial waveform (1:2 augmentation)

Letter / Represents / Rule
A / Unassisted Systolic Pressure / Must be less than (C) and more than (E)
B1,B2 / Dicrotic Notch / (B1) should be higher than (B2).
C / Augmented Diastolic Pressure / Should be higher than (A)and (E)
D / Assisted End Diastolic Pressure / Should be lower than (F)
E / Assisted Systolic Pressure / Should be lower than (A) and (C)
F / Unassisted End Diastolic Pressure / Should be higher than (D)

Table 2 – Identifying important points on the Intra-Aortic Balloon pump waveform

IABP Rules of the waveform:

1. Unassisted Systolic BP (A) > Assisted (balloon deflation) Systolic BP (E)

2. Augmented (balloon inflation) Diastolic BP (C) > Unassisted Systolic BP (A)

3. Unassisted End Diastolic BP (F) > Assisted (balloon deflation) End Diastolic BP (D)

4. Dicrotic notch on balloon inflation (B1) > Dicrotic notch without balloon inflation (B2)

Rule # / Violation / Timing Error
1 / A = E / Early deflation
2 / A => C / Early inflation (Check slope of balloon inflation) or
Late inflation (Look for “W” at balloon inflation)
3 / F < D / Late deflation
4 / B1 = B2 / Late inflation (Look for “W” at balloon inflation) or
Early deflation

Table 3 – Rules violations and the timing errors they can cause