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IABP

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Intra-aortic balloon pumping

Beneficial effects

  • reduces cardiac work by decreasing afterload
  • increases coronary blood flow

Basic mechanism

  • placed in the thoracic aorta
  • balloon inflated during diastole, thus increasing aortic pressure during diastole and increasing coronary blood flow
  • balloon deflated prior to and during early left ventricular ejection thus reducing aortic pressure and thus afterload

Indications

Indicated in the following conditions if further medical treatment judged likely to be ineffective:

Also useful in:

  • high risk patients undergoing PTCA
  • ventricular arrhythmias refractory to conventional treatment
  • patients at high risk of cardiac decompensation during non-cardiac surgery

Contraindications

  • aortic insufficiency
  • aortic dissection
  • (prosthetic graft in thoracic aorta)
  • severe aortoiliac disease

Practical aspects of use of balloon pumps

Drive units

  • operation is based on recognition of the fact that the interval between electrical and mechanical events of cardiac cycle is variable, varying from patient to patient and in a given patient, with heart rate
  • in a given patient the systolic time interval at a given heart rate can be used to predict the STI at other rates. Drive units are preprogrammed with families of STI/heart rate curves. At the initiation of pumping the operator estimates the intervals from the QRS complex to aortic valve opening and closure and enters them into the machine. The drive unit then selects the STI/heart rate curve that most adequately corresponds to those values to calculate balloon timing parameters
  • current drive units unable to realise maximal benefits of IABP during many arrhythmias

Balloon catheters

  • 30-40 ml displacement volume
  • usually have central lumen concentric with and inside the helium channel. Leads to catheter tip and allows use of guide wire to introduce catheter and also allows recording of central arterial pressure, thus eliminating need for a separate arterial line to obtain waveform required for IABP

Insertion

  1. heparinise patient prior to insertion of catheter providing there are no contraindications such as recent surgery. After cardiac surgery patient should be given low-molecular weight dextran at 20 ml/hr instead of heparin. (Do not exceed total daily dose of 10 ml/kg)
  2. prep skin
  3. fully collapse balloon applying 30 ml vacuum with 60 ml syringe
  4. insert needle into femoral artery at 45° and pass it through both walls of artery. Withdraw needle until strong pulsatile jet of blood is obtained
  5. pass guidewire through needle and advance until tip is is in thoracic aorta. Wire should pass very easily
  6. pass sheath over wire in similar manner to insertion of PA catheter sheath
  7. pass balloon over guidewire through sheath. Must be inserted to at least the level of the manufacturer’s mark (usually double line) to ensure that entire balloon has emerged from sheath
  8. balloon should be positioned so that the tip is about 1 cm distal to the origin of the left subclavian artery. If fluroscopy is not available during insertion the distance from the angle of Louis down to the umbilicus and then to the femoral artery insertion site should be measured to approximate the distance the balloon should be advanced and the position should be checked on CXR
  9. remove wire. Return of blood via central lumen confirms that the tip is not subintimal and has not caused a dissection.
  10. flush central lumen with heparin saline and connect to transducer to monitor intra-aortic pressure
  11. monitor Doppler ankle pressures and compare with preinsertion value

Balloon pump timing

  • using central aortic pressure waveform and ECG identify dicrotic notch (aortic valve closure)
  • determine time delay between R wave and aortic valve opening and closure and enter these values into the pump
  • turn on pump and compare assisted and unassisted waveforms to determine whether timing is optimal (figure 1)
  • if inflation is too early or deflation too late the balloon waveform is superimposed to varying degrees over the LV systolic component of the central aortic pressure waveform (ie inflation starts when the aortic valve is still open). This results in an increase in afterload which may result in premature valve closure and increase LV work. Also, ventricular emptying is incomplete, stroke volume decreased, cardiac output decreased and myocardial oxygen demand increased. In addition, can increase shunting in patients with a septal defect
  • if inflation is too late or deflation is too early diastolic augmentation is suboptimal
  • balloon inflation can be triggered by R wave, arterial waveform or pacing spike. Latter is a potentially lethal mode as loss of capture may result in balloon inflation during systole as the pump will continue to follow the pacing rate rather than the ventricular contraction rate

Complications

During insertion

  • failure to advance catheter beyond iliofemoral system because of atherosclerotic disease (most common complication)
  • aortic dissection and arterial perforation

During use

  • limb ischaemia most common. Sufficiently severe to require removal of balloon in 11-27%
  • sepsis. Relatively unusual but associated with high mortality. Positive blood cultures require prompt removal and culture of IAB and treatment with antibiotics
  • thrombocytopaenia
  • embolization of platelet aggregates from surface of balloon and cholesterol emboli
  • balloon rupture leading to embolization of helium (2-4%). May be heralded by high balloon inflation pressures. Blood in connecting tubing is hallmark of rupture and requires immediate cessation of counterpulsation, placement of patient head down and IAB removal. Antibiotic cover should be broadened as the gas chamber of the balloon is not sterile.
  • small perforation in balloon membrane may allow small leak of blood into balloon lumen. Dry helium dessicates the collected blood which then forms a hard pellet which may prevent removal of balloon except by surgical aortotomy.

During or following removal

  • haematoma
  • false aneurysm
  • AV fistula

Further reading

Cutler BS, The Intraaortic Balloon and Counterpulsation. In Rippe 3rd ed

 


© Charles Gomersall July 1999

 

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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