Normal IABP 1:2 assist: diastolic augmentation and decreased end-diastolic pressure
Rapid deflation just before aortic valve opening reduces left ventricular diastolic pressure (afterload) and therefore wall tension and ↓ MVO2 demand) .
The cardiac output is augmented by about 40%, and the left ventricular stroke work is decreased and therefore the myocardial oxygen demand. These effects may be quite variable, and they depend upon the volume of the balloon, its position in the aorta, heart rate and rhythm, the compliance of the aorta, and synchronization with the cardiac cycle [2, 3].
The most commonly used triggers are the ECG and arterial waveform.
Balloon inflation (onset of diastole after aortic valve closure): middle of T wave on the ECG and the dicrotic notch on the arterial waveform.
Balloon deflation (onset of systole just before aortic valve opening): peak of R wave or just before the systolic upstroke on the arterial waveform .
Augmentation of diastolic pressure during balloon inflation improves coronary circulation, and the presystolic deflation of the balloon reduces the resistance to systolic output and decreases myocardial work. The overall effects of the IABP therapy in this patient are an increase in the myocardial oxygen supply/demand ratio and improved forward flow and decreased mitral regurgitation.
Both helium and carbon dioxide have been used as driving gases; however the use of helium has theoretical advantages because it is less dense facilitating rapid transfer to and from the console. Both helium and carbon dioxide are easily absorbed into the bloodstream (compared to nitrogen and oxygen) in case of rupture of the balloon .
The closer the balloon is to the aortic valve, the greater the diastolic pressure elevation. It is obvious that local anatomical factors limit the position of the balloon within the aortic arch; therefore the optimal balloon position is situated distal to the left subclavian artery take off. Incorrect balloon position results in reduced diastolic augmentation and increases vascular morbidity.
With optimal IABP position, on CXR, the tip is seen just below the aortic knob or at 2 cm above the carina. The position can also be confirmed by transesophageal echocardiography .
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Complication of IABP:
Vascular complications: including limb (and visceral) ischemia, vascular laceration, major hemorrhage, and arterial dissection
Position complications including obstruction of arterial flow causing visceral ischemia
Air or plaque embolism
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