Source: Critical Care Challenges, Lippincott Williams & Wilkins, 2003.
AN INTRA-AORTIC BALLOON PUMP (IABP) provides temporary support for the heart's left ventricle by mechanically displacing blood within the aorta.
This device may be used in patients with a wide range of disorders that cause low cardiac output (CO) or cardiac instability, such as refractory angina, ventricular dysrhythmias associated with ischemia, pump failure caused by cardiogenic shock, intraoperative myocardial infarction (MI), or low CO after bypass surgery.
The IABP also is indicated for patients with low CO secondary to acute mechanical defects after MI, such as ventricular septal defect, papillary muscle rupture, or left ventricular aneurysm.
In normal inflation-deflation timing, balloon inflation occurs at the onset of diastole, after aortic valve closure; deflation occurs during isovolumetric contraction, just before the aortic valve opens. In a properly timed waveform, as shown, the inflation point lies at or slightly above the dicrotic notch. Both inflation and deflation cause a sharp V shape. Peak diastolic pressure exceeds peak systolic pressure; peak systolic pressure exceeds assisted peak systolic pressure.
The accompanying illustrations will help you use arterial pressure waveforms to determine whether your patient's IABP is functioning properly.
The inflation point lies before the dicrotic notch, during systole, before the aortic valve is closed, which dangerously increases myocardial stress and decreases CO.
With early deflation, a U shape appears and peak systolic pressure is less than or equal to assisted peak systolic pressure. This won't decrease afterload or myocardial oxygen consumption.
With late inflation, the balloon inflates after the aortic valve closes. The dicrotic notch precedes the inflation point, and the notch and the inflation point create a W shape. This can lead to a reduction in peak systolic pressure and coronary perfusion pressure.
With late deflation, peak systolic pressure exceeds assisted peak systolic pressure. This threatens the patient by increasing afterload, myocardial oxygen consumption, cardiac workload, and preload. It occurs when the balloon has been inflated too long or inflates at the beginning of ventricular ejection. As a result, the left ventricle has to eject blood against the resistance of the inflated balloon.