Equipment

Historically, the adult IABP consisted of an 8.5F to 12F catheter, the distal 30 cm of which was covered with a polyurethane balloon. For adult patients, 7F catheters also with 25-mL to 50-mL balloons are currently most commonly used, with the size of the balloon dependent upon the patient’s height. The pediatric catheter is 4.5F to 7F with a 2.5-mL to 12-mL balloon.

The catheter is inserted into the common femoral artery percutaneously by the Seldinger technique or by an open surgical procedure. It is then threaded proximally so that the balloon lies high in the descending thoracic aorta, just distal to the origin of the left subclavian artery.

The catheter is connected to a drive console that has a pneumatic pump that uses helium to rapidly inflate the balloon and, just as quickly, deflate the balloon after a brief period of time. Balloon cycling is triggered either from the electrocardiogram R wave, inflating with diastole and deflating with onset of systole (Figure 153-1), or from the aortic pressure waveform. It should be adjusted to inflate when the dicrotic notch occurs in the pressure cycle (Figure 153-2). The balloon can be set to trigger with every beat, every other beat, or some other pattern.

Hemodynamic effects

With balloon deflation at onset of systole, the peak aortic systolic pressure falls 10% to 15% (systolic unloading) and inflates immediately with appearance of the dicrotic notch. Balloon inflation can increase intraaortic diastolic pressure by approximately 70%. The cardiac index increases 10% to 15%, whereas the pulmonary artery occlusion pressure falls by a similar amount. Coronary blood flow increases as a result of increased diastolic pressure.

As the balloon deflates, a decrease occurs in the pressure in the aorta in proximity to the balloon, reducing the systemic vascular resistance, which, in turn, reduces myocardial O₂ demand and a shift of the Starling curve to the right. These effects can last as long as 48 to 72 h after initiation of the balloon counterpulsation.

Indications

The IABP is used primarily for treatment of acute cardiac failure refractory to pharmacologic intervention. Most commonly, it is used for low-output states associated with acute coronary syndromes and after cardiopulmonary bypass. The pump can also be placed preoperatively when the surgical stress is anticipated to exceed the functional capacity of a diseased heart. In very high-risk heart operations, the elective preoperative placement of an intraaortic balloon and initiation of counterpulsation can improve the patient’s prognosis. In recent years, the IABP has also found use as a temporary bridge to cardiac transplantation, to placement of a left ventricular assist device, or to placement of a total artificial heart.

Approximately 3% to 4% of patients undergoing cardiopulmonary bypass need IABP support. If the patient is not hypovolemic and the heart rhythm is suitable for IABP use, the criteria listed in Box 153-1 can be used to determine appropriate initiation of IABP support.

Contraindications

The classic contraindications to the use of intraaortic counterpulsation are severe aortic insufficiency, severe peripheral vascular disease, thrombocytopenia (platelet count <50,000), contraindication to anticoagulation, acute stroke, and active bleeding.

Weaning from intraaortic balloon pump support

Following resolution of the problem for which the intraaortic balloon was placed, patients have traditionally been weaned from IABP support by a gradual reduction in augmentation rate (1:1, then 1:2, then 1:3, etc.). Most hemodynamic changes occur while going from 1:1 to 1:2 augmentation. To institute a more gradual reduction in circulatory assist and to reduce the risk of thrombus formation around a static balloon, an alternate weaning approach is to maintain a 1:1 augmentation rate but gradually reduce the degree of balloon inflation because the rate and degree of deflation are determined by changes in the intraaortic diastolic pressure.

Complications

Previously reported complication rates with the use of IABP were 5% to 27%, but more recent reviews suggest a complication rate around 3% to 4%. Placement of a large catheter in the common femoral artery can occlude the artery, which is manifested by a loss of distal pulses; the aortotomy site can bleed; or the site can become infected. The relative frequency of each of these complications varies widely among reports, and the literature is inconsistent as to the impact of chronic placement on complication rates. Nevertheless, it may be reasonable to expect up to a 9% incidence of bleeding or vascular compromise in these patients. These complications may readily become life threatening.

Outcome

Clinicians have evaluated immediate and long-term prognosis following IABP support with the aim of identifying reliable determinants of survival but have made their assessments using nonrandomized groups. The primary determinant of survival after use of an IABP is early recovery (within 24 h) of cardiac function with maintenance of vital organ perfusion. Conversely, the use of inotropes, direct current cardioversion, chronic left ventricular failure, and the functional severity of the patient’s heart disease have been associated with poor outcome.

Theoretically, the predicted improvement in the O₂ demand-supply ratio offered by IABP support can benefit patients with acute cardiac decompensation. Nevertheless, it remains to be determined to what extent IABP will improve survival and for whom this technology is best used.