Page 650 - Cardiac Nursing

626 P AR T IV / Pathophysiology and Management of Heart Disease

Contraindications
Because inflation of the balloon during diastole increases pressure
in the aortic root, significant aortic regurgitation is a contraindi-
cation to IABP therapy. Inflation would otherwise increase regur-
gitation and thus LV workload. The presence of an aortic
aneurysm is also a contraindication to IABP therapy. Trauma or
rupture of the aneurysm can occur during IABP insertion. Dis-
lodgement of adjacent thrombus can occur during insertion or
from balloon inflation resulting in embolization. These risks are
all unacceptable. Severe peripheral vascular occlusive disease in the
femorial or iliac artery contraindicates IABP therapy. Catheter in-
sertion may be difficult or impossible, and occlusion of the
affected vessel, dissection, and dislodgement of plaque from the
vessel wall are all possibilities as well. These potential problems
can be avoided by selecting an alternate method of insertion. In
the cardiac surgery patient, the catheter may be inserted directly
into the thoracic aorta, although this method requires reopening n Figure 26-5 Criteria for effective intra-aortic balloon pump
the sternotomy incision to remove the catheter. The catheter can (IABP) timing: (1) inflation occurs at the dicrotic notch; (2) the slope
also be placed antegrade in the aorta via the right subclavian/ of rise of balloon inflation is straight and runs parallel with the pre-
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axillary artery. This approach requires a subperiosteal clavicular ceding systolic upstroke; (3) augmented diastolic pressure is at least
resection to access the artery, but is less invasive than a sternotomy equal to the preceding systolic pressure; (4) end-diastolic pressure at
incision. Newer catheters of smaller diameter minimize the risk of balloon deflation is lower than the preceding unassisted end-diastolic
pressure; (5) the next systolic pressure is assisted systole and is lower
occluding distal blood flow. In addition, the ascending aorta than the preceding systole, which was not affected by balloon defla-
device described above (SupraCor) could be considered. Uncon- tion. (From Shinn, J. A. Intra-aortic balloon pump counterpulsation.
trolled sepsis and coagulopathy are other contraindications. In C. M. Hudak, B. M. Gallo, & T. S. Lohr [Eds.], Critical care nurs-
Lastly, if invasive therapies are contrary to the goals of care (e.g., ing: A holistic approach [5th ed., p. 213]. Philadelphia: J.B. Lippin-
comfort care in a patient who is very unlikely to survive despite cott, 1990.)
even heroic measures), IABP therapy should not be utilized.
ing systolic pressure. With afterload reduction, the next systolic
Proper Timing and Expected pressure after balloon deflation is lower than the systolic pressure
Clinical Outcomes with no balloon effect, which is evidence that LV workload has
been decreased. Five criteria can be used to determine the effec-
Proper timing of IABP therapy is crucial to achieving the benefi-
cial hemodynamic changes described above. Proper timing re- tiveness of IABP timing, as illustrated on the arterial pressure trac-
quires coordination of inflation and deflation of the balloon with ing (Fig. 26-5) and detailed below.
the patient’s cardiac cycle. To evaluate balloon timing properly, n Criterion 1. Inflation must occur at the dicrotic notch, which is
the assist ratio is set at 1:2, meaning the balloon is assisting every the beginning of diastole. Inflation actually should be timed to
other cardiac cycle. In this way, the observer can compare the obliterate the notch. The interval between the onset of systolic
effect of balloon inflation and deflation with unassisted beats. upstroke and the point of balloon inflation should not be
Most patients tolerate this ratio well, at least for a brief period. shorter than the interval between the systolic upstroke and di-
The R wave from the ECG, pacemaker spikes on the ECG, or the crotic notch on the unassisted beat. Inflation that occurs too
arterial systolic pressure can be used to identify individual cardiac early can abbreviate systole by causing premature aortic valve
cycles. Each can act as signals for the IABP console to discriminate closure, reducing stroke volume, and therefore cardiac output.
systole from diastole. The R wave signals the onset of electrical de- Late inflation (past the dicrotic notch) shortens the duration
polarization, which immediately precedes mechanical systole. A of assistance, thus reducing the period of maximal augmented
ventricular pacemaker spike essentially represents the same event. diastolic pressure.
Arterial systolic pressure signals the onset of mechanical systole. n Criterion 2. The upstroke of balloon inflation should be sharp
Any of these reference points can be used to determine when de- and parallel with the preceding systolic upstroke. This inflation
flation of the balloon should optimally occur. An arterial wave- creates a V-shaped appearance, with the nadir of the V being the
form is necessary to determine the onset of mechanical diastole point of inflation. The sharp upslope ensures that maximal early
and systole and to verify timing. Diastole has begun when the augmentation is occurring. A slope that is not straight may in-
dicrotic notch (which results from aortic valve closure) appears on dicate that the balloon is inflating late, perhaps mistiming off of
the arterial waveform. Balloon inflation is timed to occur at this an artifact during early diastole. In this case, the loss of the V
point in the cardiac cycle. The deflation point can be optimally configuration also is evident.
adjusted by observing the end-diastolic drop in pressure created n Criterion 3. The augmented diastolic pressure peak should be at
by balloon deflation. The goal is to create the greatest pressure least equal to the preceding systolic pressure peak. A decrease in
drop possible. Ideally, there would be at least a 10 mm Hg differ- this pressure peak may indicate gas loss from the balloon. This
ence between end-diastolic pressure without the balloon effect loss can occur by natural diffusion. A balloon normally requires
and the end-diastolic pressure created by balloon deflation. Evi- refilling every 1 to 2 hours because of natural diffusion of gas
dence that afterload reduction has occurred is seen in the follow- through the membrane. Most consoles automatically purge and