it would otherwise. Cardiac workload and myocardial oxygen demands are subsequently reduced. If the timing is not correct, these advantages are lost, and the patient may be harmed [2].
An IABP can use different triggers to time inflation and deflation cycles. Most 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. To use the arterial pressure as a trigger the patient must have an arterial pressure catheter that is connected to the balloon pump. Some IABP devices have specialized fiber optic connectors to measure arterial pressures. The ECG can also be used as a trigger mode. 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 [2].
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 (every other cardiac cycle is assisted) 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 phase (Figure 11.1). 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 [2]. Potential complications include limb ischemia, compartment syndrome, aortic dissection, bleeding, thrombocytopenia and red blood cell destruction, gas embolus, infection, and cardiac decompensation from improper timing. (Additional introduction to IABP can be found at https://www.youtube.com/watch?v=NYeA‐3AAQB4&t=100s).
Figure 11.1 IABP arterial pressure tracings with 1:1 augmentation and 2:1 augmentation respectively. A. Diastolic augmentation with increased coronary perfusion. B. Assisted aortic end‐diastolic pressure with decreased myocardial oxygen demand. C. Assisted systole. D. Unassisted aortic end‐diastolic pressure. E. Unassisted systole.
The interfacility transport team should examine the patient with particular attention to the insertion site, as well as to the extremity distal to the site. The insertion site should be examined for bleeding or protruding balloon. The catheter tubing should be examined for any blood or blood flecks, and for kinking. The limb should be examined for signs of ischemia. Any problems must be corrected before transport. 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 the aircraft or ambulance power inverter during transport. Pure battery operation should be used only to transport the patient from the vehicle to the in‐hospital destination. Special caution must be taken when transferring a patient from one model of IABP to another. There may be a difference in the balloon size, and an adapter may be needed to connect a “Brand A” catheter to a “Brand B” IABP. The balloon size should be noted and adjusted on the pump if necessary.
In the event of cardiac arrest, the IABP will lose all trigger modes, give a “Trigger Arrest” alarm, and then stop counterpulsation. If not addressed, this could result in a thrombus formation. When CPR is initiated, the IABP should be switched to “Arterial Trigger.” Effective CPR should allow the IABP to function from the arterial pressures. In the event that arterial pressures are not sufficient, the IABP should be switched to an internal trigger. This last resort tactic provides asynchronous counterpulsation and helps prevent clot formation. “Internal Trigger” mode should be stopped if there is a return of circulation and the ECG or arterial pressure mode is restarted [3].
In the event of IABP failure during transport, a large Luer‐lock syringe should be attached to the quick connector to aspirate the balloon for blood. If there is blood, then the balloon has lost integrity. Injection of anything into it will result in an aortic arterial injection. If no blood is found, use air to inflate the balloon to the volume capacity of the balloon. Then quickly aspirate the air and deflate the balloon. Repeat four to five times every 5 to 10 minutes to reduce the likelihood of thrombus formation until the pump can be repaired or replaced [2].
Non‐IABP percutaneous mechanical circulatory support devices
In addition to IABPs, there are other devices that are inserted percutaneously for temporary support of patients in acute cardiogenic shock. Unlike the IABP that improves the conditions for left ventricular function, these percutaneously placed left ventricular assist devices (pLVAD) directly assist the left ventricle. Among the most common of these devices is a transaortic intraventricular pump (Impella®) and extracorporeal pumps, including a left atrium to aorta pump (TandemHeart®) and right atrium to aorta pump (ECMO) [4].
The transaortic intraventricular pump is an axial flow pump that is inserted into the femoral artery and advanced in a retrograde fashion through the aortic valve and into the left ventricle. The device sits across the aortic valve and contains an inflow and outflow orifice. Between them is an impeller, a propeller that provides continuous blood flow from the left ventricle to the ascending aorta. Correct catheter positioning across the aortic valve is necessary for pump function. Blood is pumped from the left ventricle into the aortic root, unloading the left ventricle. This increases cardiac output and mean arterial pressure and decreases left ventricular end‐diastolic pressure, myocardial workload, and oxygen consumption [4].
The power connections for the pump motor and sensors are all contained within the catheter and connected to an external console that controls the pump and purge system. The controller console monitors both the catheter position and function of the impeller. It does not require pressure timing or electrocardiogram timing like the IABP, making it ideal for patients with arrhythmias. In addition to providing information on the location of the catheter and the flow rate of the impeller, the controller console also provides alarms related to suction events and purge pressure issues [4].
EMS clinicians are most likely to encounter these devices during interfacility transport of critical care patients. They are generally placed in patients with cardiogenic shock following acute myocardial infarction. Like the IABP, the positioning of the catheter is critical. The catheter location should be confirmed visually as sutured at a specific depth, in addition to reviewing the placement signal on the controller console. If repositioning of the catheter needs to be performed, the referring physician should do it prior to attempting transport. If the catheter becomes dislodged during transport, it should not be repositioned. Alternative support may be required. The pump also contains a purge system that prevents blood from entering the motor. It should be closely monitored during transport. Only transport teams knowledgeable about these devices should transport them without a specialist to manage the device. Knowledge about how to interpret the placement signal and how to troubleshoot the alarms by administering intravenous fluids, titrating vasopressors, or adjusting the flow of the impeller is important to a safe transport [5].
Patients with a transaortic intraventricular pump have been safely transferred between hospitals [1]. It seems likely that EMS clinicians providing critical care transport will encounter more patients with similar devices over time. There is some uncertainty about mortality outcome benefits compared to, for example, IABP therapy. However, technological advances continue, and some centers preferentially use transaortic microaxial‐flow LVADs with acceptable mortality and complication rates in place of more invasive devices [6, 7].
The left atrium to aorta extracorporeal centrifugal pump is placed percutaneously through the femoral