Intraaortic balloon pump

The intraaortic balloon pump (IABP) is a mechanical device used in the stabilization of an acutely ill cardiac diseased patient. The EMS physician or critical care transport team will most commonly encounter the device during a patient transfer from a facility with limited or unavailable cardiac surgery capabilities to a tertiary care center. The role of the IABP is to provide cardiac stabilization until definitive care can be obtained. Goals of IABP therapy include decreasing cardiac afterload, augmenting diastolic perfusion pressure, and increasing coronary artery perfusion [1]. These efforts help to improve cardiac output that can in turn improve tissue perfusion. The decrease in afterload reduces the workload on the heart, and the improved coronary artery circulation can increase oxygen supply to the myocardium.

Indications for IABPs most commonly encountered by EMS physicians are acute myocardial infarction, cardiogenic shock, ventricular aneurysm, left ventricular failure, valve or papillary muscle rupture, or a combination of these factors [2]. The patient is most commonly found in a catheterization lab, operating room, or coronary intensive care unit.

The IABP catheter is placed via an incision in the lower extremity, inserted in the femoral artery, and then advanced into the thoracic aorta. The balloon should be placed 1–2 cm distal to the beginning of the subclavian artery, and must be above the branches of the renal arteries. If the balloon is not placed correctly, occlusion of coronary, subclavian, or renal arteries could occur [1]. On a chest x-ray, the tip of the catheter should be visible between the second and third intercostal spaces. When inflated, the balloon should not completely occlude the aortic lumen, as this can damage the aortic wall and blood components [1]. Most devices have different sized balloons for patients based on weight or height. It is important to ensure the appropriate balloon volume is being used.

Absolute contraindications for an IABP include aortic dissection, abdominal aortic aneurysm, and aortic valve incompetence. Relative contraindications include bleeding disorders and atherosclerosis [1].

A patient with an IABP who requires interfacility transportation must be attended to by a specially trained team. In some cases, critical care paramedics, nurses, or physicians are trained to address IABP complications. Otherwise, it is vital that the transport team include a perfusionist or biomedical engineer.

Intraaortic balloon pump function is critically dependent on timing. The balloon is cycled in conjunction with the cardiac cycle. It is important to remember that the balloon is inflated during diastole and deflated just prior to systole. While the balloon is inflated, blood is pushed both back toward the heart, as well as further down the aorta. The result is increased blood flow to coronary and carotid arteries, and increased systemic perfusion. The balloon is deflated very rapidly, and this rapid loss of volume reduces the pressure in the aorta. The result is that the left ventricle does not contract as hard as it would otherwise. Cardiac workload and myocardial oxygen demands are reduced. If the timing is not correct, these advantages are lost, and further harm to the patient may occur [1].

The IABP can use several different triggers for the inflation and deflation cycle. The most common modalities use the ECG or the arterial pressure waveform as a trigger. The IABP may also have an internal trigger in the event of cardiac arrest. Using arterial pressure as a trigger requires the patient to have an arterial catheter placed and connected to the balloon pump. Some IABP devices may have specialized fiberoptic connectors to measure arterial pressures. It is important to note that once a fiberoptic connector is placed and zeroed, it cannot be removed and connected to a different transport IABP. Another trigger modality needs to be used, such as ECG. Most devices have an “automatic” trigger mode, where the pump automatically switches between trigger modes if needed. An example would be a switch between ECG and arterial pressure modes if the ECG signal is lost. Most modern pumps can also compensate for arrhythmias such as atrial fibrillation and pacing modes [1].

With the trigger mode established, attention should focus on timing. Most patients are transported with a 1:1 frequency, where each cardiac cycle is assisted. In order to assess timing, it may be helpful to place the device in a 1:2 frequency to get a better picture of the arterial pressure waveform landmarks. For transport, the operator should ensure that the balloon is set to inflate at the dicrotic notch, and to deflate during the next isovolumetric contraction (IVC) phase. The dicrotic notch phase on the arterial pressure waveform represents aortic valve closure and diastole. Once the timing is correct, the device can be placed back into a 1:1 frequency and put in the “automatic” mode if available [1]. Potential complications include limb ischemia, compartment syndrome, aortic dissection, bleeding, thrombocytopenia and red blood cell destruction, gas embolus, infection, and cardiac decompensation from incorrect timing [1].

Special care must be taken when transferring a patient from one brand of IABP to another to enable transport. There may be a difference in the balloon size, and an adapter may be needed to connect a “Brand D” catheter to a “Brand A” IABP. The balloon size should be noted and adjusted on the pump if necessary.

On arrival to a patient’s side, the transport team should examine the patient paying particular attention to the insertion site, as well as to the distal extremity. The insertion site should be examined for bleeding or protruding balloon. The catheter tubing should be examined for any blood or blood flecks. The distal extremity should be examined for ischemia. Catheter tubing should be examined for kinking. Any positive findings noted above should delay the transport until the situation can be corrected. Fresh ECG leads should be applied to the patient. The referring hospital balloon pump should not be disconnected or shut off until the transport pump is connected and tested. The transport balloon pump should be plugged into an outlet during this time and not run on battery power. The pump should also be plugged into an aircraft or ambulance power inverter during transport. Pure battery operation should be used only to transport the patient from the vehicle to his or her hospital destination.