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
- 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)
- prep skin
- fully collapse balloon applying 30 ml vacuum with 60 ml syringe
- 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
- pass guidewire through needle and advance until tip is is in thoracic aorta.
Wire should pass very easily
- pass sheath over wire in similar manner to insertion of PA catheter sheath
- 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
- 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
- remove wire. Return of blood via central lumen confirms that the tip is not
subintimal and has not caused a dissection.
- flush central lumen with heparin saline and connect to transducer to monitor
intra-aortic pressure
- 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
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