Intra-aortic Balloon Pumps

The intra-aortic balloon pump (IABP) is a counterpulsation mechanical support device used to provide temporary hemodynamic support to hemodynamically unstable patients in cardiogenic shock. The cardiovascular benefits of the IABP are related to the synchronized inflation and deflation of the balloon, which results in the displacement of blood in the aorta. Here we will review the IABP design & mechanics, discuss placement of the device, highlight the hemodynamic benefits of the IABP, and review IABP indications, complications and contraindications.

When should you consider inserting an IABP??

In the cardiac surgery ORs, you will most often encounter IABPs for perioperative low cardiac output syndrome. In patients with severely reduced left ventricular systolic function, the IABP will often be placed by the surgeons prior to induction, to provide hemodynamic support during the tenuous induction period and to assist in weaning from cardiopulmonary bypass. Additionally, in patients who have difficulty weaning from CPB due to poor cardiac output, placement of an IABP can play an important role in addition to inotropes. Discuss the need for IABP support with your attending in your preoperative discussions.

Design

  • IABP consists of a flexible catheter with a distal cylindrical balloon that inflates and deflates in the descending thoracic aorta
  • IABP catheter is composed of 2 lumens:
    • one lumen transduces systemic blood pressure and samples blood
    • one lumen delivers helium gas to the closed balloon system

Mechanics

  • Inflation of the balloon occurs during diastole immediately after aortic valve closure
  • Deflation occurs just before aortic valve opening and left ventricular ejection
  • Cycles of inflation and deflation are:
    • controlled by an external pump
    • synchronized to the patient’s native cardiac cycle using input from either the aortic pressure transduced from the tip of the catheter or an EKG
  • IABP augmentation is described by the ratio of IABP pulsation to native cardiac beats
    • in 1:1 augmentation, each cardiac cycle is assisted by IABP augmentation
    • in 1:2 augmentation, the IABP assists every other cardiac beat
  • Some IABP systems allow for asynchronous counterpulsation, which may be necessary in cases such as asystole, cardiac arrest, or cardiopulmonary bypass
  • Accurate IABP timing is integral to the functioning of this device and to achieving maximum hemodynamic benefit, as discussed below

Placement

  • IABP catheter is inserted into the descending thoracic aorta via the femoral artery (most commonly) and advanced until the distal tip of the catheter is 1-2 centimeters distal to the origin of the left subclavian artery.
    • other potential insertion sites: subclavian or axillary arteries
  • Vascular access can be obtained through either a percutaneous or surgical cut-down approach
  • IABP positioning is often done under fluoroscopic or transesophageal echocardiographic (TEE) guidance
  • CXR can be used to confirm or monitor the position of the IABP, with optimal positioning of the tip of the IABP below the aortic arch, which is usually between the 2nd and 3rd anterior rib spaces

Hemodynamic Benefits

  • Balloon inflation in diastole results in an augmentation of the diastolic and aortic root pressure, resulting in:
    • increased coronary perfusion pressure (has been questioned in some studies)
  • Balloon deflation just before left ventricular (LV) ejection results in a reduction of end-diastolic aortic pressure, resulting in:
    • decreased afterload, LV wall stress, LV systolic work & myocardial oxygen demand
    • increased stroke volume and cardiac output
  • Other hemodynamic effects include:
    • decreaseed peak systolic blood pressure
    • reduced LV preload and LV end-diastolic pressure
    • reduced pulmonary capillary wedge pressure
    • improved LV diastolic function
    • improved right ventricular function (decreased central venous pressure and RV end-diastolic diameter; increased RV stroke work index and RV systolic function)
  • Accurate IABP timing is integral to the functioning of this device and to achieving maximum hemodynamic benefit
    • Early IAB inflation increases systolic wall stress and LV afterload, resulting in decreased stroke volume.
    • Late IAB deflation increases afterload during early systole.

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