Intra-Aortic Balloon Pump

Intra-Aortic Balloon Pump
Photo by Robina Weermeijer / Unsplash

Take home messages

  • Don't switch it off
  • The goal is to improve blood supply to the myocardium, while also reducing its oxygen demand
  • Patients need to be anticoagulated
  • Check renal function to ensure the renal arteries are not occluded
  • Balloon pumps cause haemolysis
  • If the timing isn't right, then the patient can become very unstable

What is counterpulsation?

The balloon sits in the descending aorta, inflates during diastole, and deflates during systole.

This means that systolic blood flow to the body is unimpeded, but as soon as the heart relaxes, the balloon inflates and displaces the blood in the aorta both forwards and backwards, encouraging the blood to flow down the coronary arteries.

Then when the balloon deflates again immediately prior to systole, it causes a slight negative pressure in the aorta, reducing afterload on the left ventricle by reducing the pressure gradient across the aortic valve.

What is the Windkessel effect?

  • The 'Windkessel Effect' refers to the elastic recoil of the aortic root, generating pressure to squeeze blood down the coronary arteries in diastole. The balloon aims to supplement this.

Effects on the heart

  • Reduces systolic pressure and increases diastolic pressure in the aorta
  • Reduces end-diastolic pressure and afterload on the left ventricle
  • Increases cardiac output and hopefully coronary blood flow

What factors affect how well the balloon works?

  • The volume of the balloon - determines how much blood is displaced
  • Aortic compliance - a more compliant aorta will distend, reducing the backpressure and producing less augmentation
  • Heart rate - a shorter diastole means less balloon time and less augmentation

The Timing Sequence and Arterial Waveform

The dicrotic notch on the arterial waveform occurs when the aortic valve closes. The balloon inflates immediately after this, and then deflates again just before the valve opens in systole. This point is the lowest point of the arterial pressure waveform.

When the balloon inflates, it obstructs arterial blood flow, causing a rapid drop in blood pressure at the point of the dicrotic notch. However by increasing or augmenting diastolic pressure, it produces a large second peak, which is unsurprisingly labelled 'diastolic augmentation'.

Hopefully the diastolic augmentation will be higher than the systolic pressure.

You can then set the pump to assist every beat, every alternate beat, or any ratio that is required. As the patient's cardiovascular status improves, the support can be weaned off with less and less augmentation. It should never, however, be left deflated, as it is a huge thrombosis risk.


Indications and Contraindications for IABP

Indications:

  • Acute Myocardial Infarction
  • Refractory left ventricular failure
  • Cardiogenic shock not responding to pharmacological therapy
  • Sepsis
  • Cardiac surgery and weaning from cardiac bypass
  • Acute MR and VSD
  • Infant with cardiac abnormalities
  • Refractory unstable angina

Absolute contraindications:

  • Aortic dissection
  • Aortic regurgitation
  • Previous Aortic stenting
  • Chronic end stage heart failure deemed inoperable

Relative contraindications:

  • Severe uncontrolled sepsis
  • Severe peripheral vascular disease
  • Abdominal aortic aneurysm
  • Anatomical abnormalities or previous arterial reconstructive surgery
  • Tachyarrhythmias

The Balloon

The intra aortic balloon pump is divided in to two parts - the balloon itself and the control pump.

The polyethylene balloon is usually between 25 and 50ml and is loaded onto a double-lumen 8 - 9.5 Fr catheter.

The control pump coordinates the timing of inflation and deflation, and often uses helium for two reasons:

  • Its very low density makes it ideal for rapid inflation and deflation
  • It's very rapidly absorbed by the blood, which is helpful if the balloon ruptures

Complications

As you might imagine, inserting a large catheter into the aorta of a patient with heart problems, and then attempting to inflate and deflate a balloon to occlude the aorta in time with the heartbeat, can sometimes go wrong.

  • Balloon rupture and gas embolus
  • Haemolysis and thrombocytopenia
  • Occlusion of cerebral or renal arterial supply
  • Limb ischaemia
  • Aortic trauma or dissection
  • Bleeding and infection
  • Tamponade

What is the equation for coronary perfusion pressure?

  • Coronary perfusion pressure (CPP) = ADP - LVEDP
  • ADP = Aortic diastolic pressure
  • LVEDP = Left ventricular end diastolic pressure

References and Further Reading:

  • Murli Krishna, MBBS FRCA FFPMRCA, Kai Zacharowski, MD PhD FRCA, Principles of intra-aortic balloon pump counterpulsation, Continuing Education in Anaesthesia Critical Care & Pain, Volume 9, Issue 1, February 2009, Pages 24–28, https://doi.org/10.1093/bjaceaccp/mkn051

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Test your knowledge!

What are the haematological effects of an IABP?

  • Mechanical haemolysis can cause a reduction in haemoglobin of up to 5%
  • Mechanical platelet destruction can cause thrombocytopenia
  • There can be bleeding and vascular damage associated with insertion of the balloon itself
  • Anticoagulation with heparin can also cause thrombocytopenia and bleeding

What are the indications for insertion of a balloon pump?

  • Acute myocardial infarction
  • Refractory left heart failure
  • Cardiogenic shock not responding to pharmacological therapy
  • Refractory ventricular arrhythmias
  • Acute MR and VSD
  • Cardiomyopathies
  • Catheterization and angioplasty
  • Sepsis
  • Refractory unstable angina
  • Infants and children with complex cardiac anomalies
  • Cardiac surgery
  • Weaning from cardiopulmonary bypass

What are the relative contraindications to IABP insertion?

  • Severe uncontrolled sepsis
  • Abdominal aortic aneurysm
  • Severe peripheral vascular disease
  • Significant anatomical anomaly or arterial reconstructive surgery
  • Tachyarrhythmias

What are the absolute contraindications to IABP insertion?

  • Aortic dissection
  • Aortic regurgitation
  • Chronic end stage heart disease that isn't deemed operable
  • Aortic stent

Please explain how the balloon reduces myocardial oxygen demand

  • The work done by the myocardium can be estimated by looked at the systolic pressure curve of the left ventricle
  • This curve relates wall tension to time, and the area under the curve is called the tension time index
  • If you reduce the tension in the wall, or the duration of time for which that tension exists, then clearly the myocytes don't have to work so hard, and will consume less oxygen
  • This is why a reduced TTI = reduced myocardial oxygen demand
  • The deflation of the balloon reduces the afterload and therefore the tension of the left ventricular wall, reducing the TTI, and thus the O2 demand

Why is helium used to inflate the balloon?

  • Its very low density makes it ideal for rapid inflation and deflation
  • It's very rapidly absorbed by the blood, which is helpful if the balloon ruptures 

What are the complications of IABP?

  • Balloon rupture and gas embolus
  • Haemolysis and thrombocytopenia
  • Occlusion of cerebral or renal arterial supply
  • Limb ischaemia
  • Aortic trauma or dissection
  • Bleeding and infection
  • Tamponade

Which of the following is NOT a contraindication for the use of an intra-aortic balloon pump?

A) Aortic dissection B) Aortic aneurysm C) Severe aortic stenosis D) Severe peripheral vascular disease E) Severe pulmonary hypertension

Answer: E (Severe pulmonary hypertension) Explanation: Aortic dissection, aortic aneurysm, severe aortic stenosis, and severe peripheral vascular disease are all contraindications for the use of an IABP because they increase the risk of balloon rupture or dissection. Severe pulmonary hypertension is not a contraindication for IABP use.

Which of the following is NOT a contraindication for the use of an intra-aortic balloon pump?

  1. Aortic dissection
  2. Aortic aneurysm
  3. Severe aortic stenosis
  4. Severe peripheral vascular disease
  5. Severe pulmonary hypertension

Answer

5. Severe pulmonary hypertension 

Explanation: Aortic dissection, aortic aneurysm, severe aortic stenosis, and severe peripheral vascular disease are all contraindications for the use of an IABP because they increase the risk of balloon rupture or dissection. Severe pulmonary hypertension is not a contraindication for IABP use.


Which of the following statements about aortic balloon pumps is not true?

  1. The balloon should be inflated during diastole and deflated during systole
  2. The balloon should be inflated to a pressure of 15-20 mmHg above systolic blood pressure
  3. The balloon should be deflated if the patient's systolic blood pressure falls critically low
  4. The balloon should be deflated if the patient develops arrhythmias
  5. The balloon should be deflated if the patient's blood pressure improves

Answer

2. The balloon should be inflated to a pressure of 15-20 mmHg above systolic blood pressure

The balloon should be inflated during diastole and deflated during systole. The balloon should be inflated to a pressure of 5-10 mmHg above systolic blood pressure. The balloon should be deflated if the patient's blood pressure falls below a certain level, if the patient develops arrhythmias, or if the patient's hemodynamics improve. Inflating the balloon to a pressure of 15-20 mmHg above systolic blood pressure could result in balloon rupture or dissection.

References:

  • Murli Krishna, MBBS FRCA FFPMRCA, Kai Zacharowski, MD PhD FRCA, Principles of intra-aortic balloon pump counterpulsation, Continuing Education in Anaesthesia Critical Care & Pain, Volume 9, Issue 1, February 2009, Pages 24–28, https://doi.org/10.1093/bjaceaccp/mkn051