Intra-aortic Balloon Pump Trouble-shooting

aka Cardiovascular Curveball 007

Your ICU patient with the intra-aortic balloon pump (IABP) from Cardiovascular Curveball 005 is having a very bad night. His IABP keeps playing up. You are beginning to wonder if there a gremlin in the unit…

Gremlin

Don’t let this guy near your balloon pump (photo by Inti)

Can you fix the problems?

Warm up questions

First of all,  make sure you’re familiar with the normal IABP pressure waveform featured in Cardiovascular Curveball  #005:

IABP effects on aortic pressures

IABP effects on the aortic pressure cycle  (from www.ecp-india.net)

Q1. Which arrow corresponds to:

  • Unassisted Peak Systolic Pressure?
    B
  • Diastolic Augmentation / Augmented Peak Diastolic Pressure?
    E
  • Dichrotic Notch?
    C
  • Balloon Aortic End Diastole Pressure?
    The unlabeled arrow!
  • Assisted Peak Systolic Pressure
    D
  • Unassisted End Diastolic Pressure?
    A

Q2. What features seen on the aortic pressure waveform indicate optimal timing and function of the IABP?

Optimal timing and function of IABP has the following features:

  • inflation of the balloon occurs at the dicrotic notch (forming the sharp ‘V’)
  • the slope of rise of augmented diastolic waveform is straight and parallel to the systolic upstroke
  • the augmented peak DBP at balloon deflation exceeds or is equal to end-systolic BP
  • the balloon aortic end-diastolic BP (DBP at balloon deflation) is lower than the preceding unassisted end-DBP by 15-20 mmHg
  • the assisted SBP (following a cycle of balloon inflation) is lower than the previous unassisted SBP by 5 mmHg

The timing of IABP inflation and deflation should be manually adjusted to achieve these optimal waveform characteristics if they are absent.

[This question is repeated from Cardiovascular Curveball  #005 for emphasis!]

Scenarios

Too easy?

Well, see if you can deal with these scenarios showing a segment of the aortic pressure waveform from your patient with an IABP and a 2:1 assist ratio:

Scenario 1

This is your patient’s waveform:

IABP scenario 1

Q1. What is the cause?

Inflation of the IAB is occurring too late – it occurred well after the dicrotic notch (B).

Q2. Describe the waveform and the abnormalities.

Waveform features:

  • Inflation of the IAB occurs after the dicrotic notch ( B)
  • Absence of a sharp V at the point of IAB inflation (should occur at B – the dicrotic notch)
  • The augmented DBP (peak C) is less than the unassisted SBP (peak A) – it should be higher

Q3. What are the physiological effects?

Suboptimal augmentation of DBP (peak C) means that coronary perfusion may be inadequate.

Q4. How can you correct this?

Adjust the timing so that the IABP inflates at the dicrotic notch.

Scenario 2

This is your patient’s waveform:

IABP scenario 2

Q1. What is the cause of the waveform abnormalities?

Deflation of the IAB is too early – it occurred well before the onset left ventricular contraction and the start of systole.

Q2. Describe the waveform and the abnormalities.

Waveform features:

  • There is a sharp drop in pressure immediately following the peak of diastolic augmentation (peak B).
  • Diastolic augmentation may be suboptimal but it is difficult to confirm in the absence of a pressure scale or comparison to an unassisted waveform.
  • Assisted aortic end-diastolic BP may be sub-optimally increased (trough C), but it is difficult to say based on the information given. With early deflation a widened U-shaped trough is typically seen. Early deflation can  lead to an assisted aortic end-diastolic BP that equals or exceeds the unassisted aortic end-diastolic BP (trough F), although this is not the case in this scenario.
  • Assisted SBP (peak D) is the same or higher than the unassisted SBP (peak A) – it should be slightly less.

Q3. What are the physiological effects?

Early IAB deflation may result in:

  • inadequate coronary perfusion, with the potential for retrograde coronary blood flow. This may result in angina due to decreased myocardial oxygen supply.
  • suboptimal afterload reduction and increased myocardial oxygen demand.


Q4. How can you correct this?

Prolong the IAB inflation time, so that it deflates at the end of diastole,  just before the onset of isovolumetric systolic contraction.

Scenario 3

This is your patient’s waveform:


Q1. What is the cause of the waveform abnormalities?

Inflation of the IAB is occurring too early – it occurred prior to aortic valve closure (indicated by the absence of a dicrotic notch).

Q2. Describe the waveform and the abnormalities.

Waveform features:

  • Diastolic augmentation (peak B) encroaches on the peak corresponding to unassisted systole (peak A) – the two peaks have merged and are barely distinguishable.
  • There is no ‘sharp V’ or dicrotic notch between peaks A and B.

Q3. What are the physiological effects?

Early IAB inflation may result in:

  • Premature closure of the aortic valve and possible aortic regurgitation, thus impairing left ventricular emptying. There may be an increase in LVEDV, LVEDP and PCWP.
  • Increased left ventricular wall stress (afterload) and increased myocardial oxygen consumption will occur.

Q4. How can you correct this?

Delay the onset of IAB inflation, so that it inflates at the dicrotic notch resulting in a ‘sharp V’ (see the normal pressure waveform).

Scenario 4

This is your patient’s waveform:

IABP scenario 4

Q1. What is the cause of the waveform abnormalities?

Deflation of the IAB is occurring too late – deflation is occurring as the aortic valve is opening.

Q2. Describe the waveform and the abnormalities.

Waveform features:

  • The peak corresponding to diastolic augmentation (peak C) is widened.
  • Assisted aortic end-diastolic BP (trough E) is the same as, not lower than, the unassisted aortic end-diastolic BP (trough G).
  • The upstroke of assisted systolic BP (peak F) has a gentle gradient resulting in a prolonged rise.

Q3. What are the physiological effects?

Late deflation of the IAB has these effects:

  • There is no afterload reduction. The inflated balloon may actually impede left ventricular ejection and increase the afterload.
  • Myocardial oxygen consumption will increase because the left ventricle experiences a longer period of isovolumetric contraction (when most myocardial oxygen consumption occurs) and has to contract against greater resistance (afterload).

Q4. How can you correct this?

Shorten the IAB inflation time, so that the IAB deflates at the end of diastole – just before isovolumetric contraction of the left ventricle.

Scenario 5

After struggling all night optimizing the timing of the balloon pump, the patient develops atrial fibrillation with intermittent ventricular ectopy.

Q1.What problems will this cause for the intra-aortic balloon pump?

Triggering of the IABP is usually set according to the patient’s ECG tracing. When an R wave is detected the balloon is triggered to automatically start inflating in the middle of the T wave.

Triggering can be impaired if the patient develops an arrhythmia, is paced or has a poor ECG trace.

Q2. What can be done about it?

If the IABP cannot be successfully triggered using the R waves from the ECG trace, pacing spikes or the arterial blood pressure waveform may used for triggering. Alternatively, the pump can be set at an intrinsic rate without any physiological triggering. The IABP may automatically use these other modes as default backups if ECG-triggered timing is not possible.

If the patient remains hemodynamically stable despite the IABP malfunctioning it might be a good time to think about removing the IABP… Treating any underlying causes of arrhythmia is also a good idea!

References and Links

  • Datascope’s IABP elearning modules
  • Gomersall C. Intra-aortic balloon pumping. 1999.
  • Krishna M, Zacharowski K. Principles of Intra-Aortic Balloon Pump Counterpulsation. Cont Edu Anaesth Crit Care & Pain. 2009;9(1):24-28.
  • Life in  the Fast Lane: Paul Young’s ICU Mind Maps – Intra-Aortic Balloon Pump [pdf]
  • Marino PL. The ICU Book (3rd edition). 2007; Wolters Kluwer.
  • Overwalder PJ. Intra Aortic Balloon Pump (IABP) Counterpulsation. The Internet Journal of Perfusionists. 2000;1:(1) (fulltext online) [Scenarios 1-4 are based on a figure from this article]

The IABP waveforms in each of the scenarios were drawn using the excellent open-source vector graphics editor Inkscape.

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Comments

  1. Inspire says

    Unassisted Peak Systolic Pressure should actually be D. The beat before is unassisted, therefore the following systole is unassisted.

    • says

      The labels are correct -- assisted systole follows the augmented peak diastolic pressure.
      It seems paradoxical, but the assisted peak systolic pressure should be lower than the unassisted systolic peak that precedes it. However, the pulse pressure is preserved or higher due to the low Balloon Aortic End Diastole Pressure.
      Hope that helps,
      Chris

  2. Val says

    Inspire is right, assisted systolic and unassisted systolic are mislabled. This has caused great confusion amongst people in my class looking at this site. Any chance this could be corrected here? The rest of the timing exercises were great and I wish I could refer it to people who want more practice but the mistake at the beginning limits it’s usefulness.

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