Wednesday, September 15, 2010

Intra-aortic baloon pump - some useful tips

IABP  was first tried in humans in 1968 by Dr. Kantrowitz (also did the first Cardiac transplant in USA).
Basic principle - Counterpulsation -It is balloon inflation in diastole and deflation in early systole. Balloon inflation causes 'volume displacement' of blood within the aorta, both proximally and distally. This leads to a potential increase in coronary blood flow and potential improvements in systemic perfusion.


Physiological effects -  The primary aim is to improve the LV function by augmenting the coronary blood flow.  IABP inflates at the onset of diastole, thereby increasing diastolic pressure and deflates just before systole, thus reducing LV afterload. The magnitude of these effects depends upon:
        1.Balloon volume: the amount of blood displaced is proportional to the volume of the balloon.
        2.Heart rate: LV and aortic diastolic filling times are inversely proportional to heart rate; shorter diastolic time produces lesser balloon augmentation per unit time.
        3.Aortic compliance: as aortic compliance increases (or SVR decreases), the magnitude of diastolic augmentation decreases.( so beneficial in elderly with stiff arteries than a young elastic aorta)


Indications are... where you need an increase in coronary flow to augment LV function. Its more important to know the absolute contraindications -  Aortic regurgitation, aortic dissection, aortic or popliteal stents, very poor prognosis. Also be careful in pts with peripheral vascular disease.


 Waveform -  The balloon is inflated with Helium so that it quickly travels from pump to balloon...and also gets absorbed in blood incase of balloon rupture. The console uses the EKG waveform &/or systemic arterial waveform as a trigger for inflating the balloon. The balloon inflates with the onset of diastole, which corresponds with the middle of the T-wave(dicrotic notch on arterial wave). The balloon deflates at the onset of LV systole and this corresponds to the peak of the R-wave. Since the distal aortic pressure drops with inflation, you can see a slight dip at the dicrotic notch followed by a second peak due to augmentation of the diastolic pressure ( which should be more than the pts systolic pressure denoted by the peak before the dip @ dicrotic notch). Have a look at the figure.


Monitoring - Depending on hemodynamic status..the inflation can happen with each beat (1:1) or every other beat(1:2) & so on. Keep all these patients on heparin anticoagulation. And importantly monitor their Urine output. If it drops suddenly...confirm the position of the tip of balloon (2cm above carina) with an Xray..as the balloon may be adjacent to the renal artery. Once patient's pressor needs have gone down..start weaning them from IABP by reducing the rate of augmentation 1:2 to 1:3 and so on. 
Hope this helps!!

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