Intra-Aortic Balloon Pump
In 1958 the idea of counterpulsation to treat left ventricular failure was introduced by Harken. He theorized that the workload of the heart could be reduced and coronary perfusion could be increased simultaneously.
By 1962 Moulopoulus, Topaz, and Kolff, working together at the Cleveland Clinic, had developed the first intra-aortic balloon. Shortly thereafter Kantrowitz presented the first intra-aortic balloon pump (IABP). In 1985 the development of the first prefolded balloon occurred, greatly improving the process of placing the balloon.
The concept behind the IABP is counterpulsation, or, simply put, forcing the oxygen-rich blood being pumped out of the heart to reverse course and flow into the coronary arteries. This is achieved by inserting a balloon into the patients femoral artery (in the groin area) and threading it into the aorta. Proper placement is to have the tip of the balloon in the distal arch approximately 2 cm below the subclavian artery. (If the balloon is too close to the heart, it can cause an obstruction in the flow of blood to the brain.)
Once the balloon is in place, it can be inflated and deflated rapidly to achieve the desired effect. With correct timing, the blood is forced into the coronary arteries, supplying the heart with more oxygen. The deflation of the balloon prior to the next cycle produces a lower pressure for the heart to pump against. Thus, the heart is receiving more oxygen while performing less work. Balloon therapy is a short-term procedure designed to allow the heart to gain strength and recover faster.
The balloon itself is made of polyethylene and is attached to a catheter. Several sizes and lengths of balloons are available to accommodate various patients. Balloon designs also vary. Some balloons have as many as three separate chambers. With this design, the middle section is inflated first, and then the ends simultaneously inflate. Another design has two sections, wherein the distal-end section inflates first to occlude the aorta, and then the main body inflates, forcing a backward flow of blood. There are also single-section balloons. Many balloons now have pressure transducers mounted at the tip to give accurate arterial pressure readings to the operator.
The balloon is inflated with a carefully measured volume of gas, usually helium or carbon dioxide. Helium, having the smallest molecules, gives the fastest inflation/deflation times, while carbon dioxide is more readily absorbed into the body in the event of a ruptured balloon, indicated by blood in the catheter.
The inflation and deflation of the balloon are timed to the cardiac cycle (generally synchronized with the electrocardiogram) to give the greatest benefit and to prevent backflow through the aortic valve. The ECG wave or the arterial waveform can be used to determine the inflation and deflation point. The balloon should be inflated just after the aortic valve closes. The dicrotic notch is the visual indication that the valve has closed and can be used to set up the timing. The R-wave, indicating ventricular contraction, is commonly used to trigger inflation. Deflation can be timed or triggered but must occur before the next cardiac cycle.
Preventive maintenance includes verifying triggers and battery runtime, rebuilding pumps, emptying water traps, and checking for pneumatics leaks. Inspection of the tank yoke for damage , leaks and correct pin index should also be included. Remember your color codes for medical gases and verify the correct tanks are being used. ( Helium tanks are brown and carbon dioxide tanks are gray.) A knowledgeable technician using the manufacturers specific procedures should perform preventive maintenance.
Common faults associated with IABPs include helium leaks, condensation problems within the catheter, patient lead placement, and timing problems. Modern pumps have the ability to trigger from internal ECG or arterial pressure waves, and many can also use external sources of these waveforms. Occasionally the external signal will be delayed," causing incorrect inflation or deflation triggers. If the pump fails to trigger on the ECG wave, the user should trigger the arterial waveform.
Occasionally a balloon will rupture, allowing the machine to draw blood into the catheter, and if not detected, into the IABP itself. All parts of the pump that have direct contact with the patient portion of the machine should be replaced if fluid intrusion occurs.
|1. What color is a helium tank?
2. Blood in the catheter indicates_______________
3. If the balloon is placed too high (too close to the heart), what could happen?
4. If the pump will not trigger on the ECG wave, you should______________________
5. IABPs are used to_____________________
Answers: 1a; 2b; 3b; 4c; 5d
Glen L. Wolfe, CBET, CET, is lead technician at LaGrange (Ill) Memorial Hospital. He has worked in the field for 12 years and holds an AA in biomedical technology. He is a graduate of the US Army medical equipment repair school.