Ventricular assist devices (VADs) are increasingly being used in pediatric patients to support cardiac failure as a bridge to transplant or recovery.1,2 The EXCOR pediatric VAD (Berlin Heart GmbH, Berlin, Germany) is a pulsatile, pneumatic, paracorporeal blood pump actuated by the Ikus stationary driving unit. The range of pump sizes (10–60 ml for pediatric patients; 80 ml for adults) and the capability of providing univentricular or biventricular configurations allow for the support of a large variety of patient sizes and physiologies. The EXCOR pediatric VAD is currently the only Food and Drug Administration (FDA)-approved pediatric VAD available in the United States and the only long-term VAD available for babies and infants. Food and Drug Administration indications for use state only that the patient must be a candidate for transplantation and does not place restrictions on the transplant capabilities of the implanting medical center.3 Nontransplanting institutions may be able to use this technology with a predetermined agreement to transfer the patient to a partnering transplant center. In addition, as more centers adopt this technology, there may be an increased need to transport these patients over long distances to facilitate patient care and organ transplantation. We report the first two cases of interhospital air transport of nonambulatory or intubated pediatric patients implanted with EXCOR pediatric VADs and supported by the Ikus stationary driving unit. We describe our process for transporting this delicate patient population, identifying important challenges encountered during transfer, and provide potential solutions.
A 1-month-old Caucasian female (patient 1; Table 1) was diagnosed with dilated cardiomyopathy secondary to a tropomyosin gene mutation. In October 2009, at 2.5 years of age, an echocardiogram (ECHO) revealed severe global left ventricular (LV) dysfunction and severe LV dilation requiring milrinone and dopamine support. In December, the patient was implanted with a 25 ml Berlin Heart EXCOR pediatric left ventricular assist device (LVAD; Berlin Heart Inc.) cannulated from the LV apex to the ascending aorta due to progressive decline. At the time of implantation, the patient was 91 cm and 12.5 kg (Body Surface Area [BSA] = 0.56 m)2 and had an ejection fraction (EF) of 17%.
By request of the family, the patient was transferred to Children’s Hospital of Pittsburgh (CHP) by our specialized pediatric critical care transport team on May 14, 2010. At the time of transport, the patient was hemodynamically stable, extubated on room air, and alert but remained in the intensive care unit at the implanting hospital. Anticoagulation therapy was being managed with the Edmonton protocol. Sedation and anxiolysis were ensured during transportation to reduce anxiety, especially during transition between vehicles. The patient was continually monitored for airway compromise, and half-way through the flight, the patient was placed on 100% blow by oxygen for low oxygen saturation. A volume bolus of saline was administered on landing to aid LVAD filling. No changes to the LVAD pump settings were necessary during transport. We did not detect any changes in pump operation due to elevation or pressurization, and we also did not experience any electromagnetic interference between the aircraft and the Ikus driver.4–7 Total patient travel time was 5 hr, with 1.5 hr of flight time. Total transport distance for the patient was approximately 550 miles. Post-transport clinical course was uneventful, and on June 19, 2010, the patient underwent successful orthotopic heart transplantation after 184 days of LVAD support.
A 5-month-old Hispanic female (patient 2; Table 1) was admitted to a referring hospital with nonsustained supraventricular tachycardia, which was supported with amiodarone, milrinone, and nipride, and required intubation. After an episode of pulseless ventricular fibrillation resulting in chest compressions and defibrillation, an ECHO revealed severely dilated left atrium and LV and EF of 21%. The patient was subsequently placed on extracorporeal membrane oxygenation (ECMO) support on September 12, 2010, and 5 days later was implanted with Berlin Heart EXCOR pediatric bi-VADs (both 10 ml; right ventricular assist device [RVAD] cannulated right atrium to pulmonary artery; LVAD cannulated LV apex to ascending aorta). At the time of implant, the patient was 6 months old, 62 cm, and 6.45 kg (BSA = 0.33 m2) and diagnosed with congenital heart disease with a noncompacted LV. Before transfer to CHP, the patient required three LVAD pump changes due to clot formation.
On January 28, 2011, our specialized pediatric transport team transferred the patient to CHP. At the time of transport, the patient was intubated and mechanically ventilated, sedated, and being supported with intravenous medications for RV failure and pulmonary hypertension, as well as bivalirudin for anticoagulation. Thrombus deposition was visible near the outflow valve in the LVAD, and a large clot was visible near the outflow valve of the RVAD; neither clot was dislodged nor changed during the transport. At the start of the transport, the ventilator rate was changed from 30 to 25 rpm, and immediately before flight takeoff, the ventilator fractional inspired oxygen was increased from 50% to 100%. No medication changes were made during the transport other than induced paralysis and increased sedation during transfers between vehicles. No changes to either pump settings were necessary during transport. We did not detect any changes in pump operation due to elevation or pressurization, and we also did not experience any electromagnetic interference between the aircraft and the Ikus driver.4–7 Total patient travel time was 5 hr, with 1.5 hr of flight time. Total transport distance for the patient was approximately 350 miles.
Post-transport clinical course included two RVAD pump changes due to thrombosis and eventual extubation to high flow nasal cannula. On February 15, 2011, the patient underwent successful orthotopic heart transplantation after 151 days of biventricular VAD support.
Early adult VAD reports described the difficulties of safely moving large, low-mobility machines with short battery support times.8,9 Technological advances have enabled the design of smaller and more portable adult VADs such that out-of-hospital discharge and interhospital transfers have become commonplace.10 Unfortunately, this technology is not yet available for pediatric patients. Although some adult VADs may be implanted into adolescent patients,11 most pediatric patients will likely continue to be implanted with the EXCOR pediatric VAD and Ikus driver until other options become available.12 The EXCOR pediatric VAD does have an optional mobile driver (with a reduction in size weight and an increase in battery life); however, this unit is only available for the 50, 60, and 80 ml pump sizes.13 Most EXCOR pediatric VAD patients are implanted with smaller pump sizes and can only be supported by the Ikus stationary driving unit, a 93 kg rectangular driver consisting of three compressors, two processors and a laptop. Although the Ikus is adequate for the hospital environment as a stationary support device, transportation by ground or air ambulance requires additional planning to account for large size and short battery life (30 min with a recharge time of 6 hr) of the driver.
In our experience, transportation of each patient was a complex process, involving a range of resources from personnel and logistics to technical device requirements; however, both transports were similar in terms of planning and provide a framework for future transports. Upon acceptance of the request for transfer to our institution, we contracted an air ambulance service that provided a Gulfstream G-III intensive care unit aircraft, pilots, and a flight nurse, as well as guidance on waivers and permissions needed for each airport (Phoenix Air Group, Inc., Cartersville, GA). We also notified the FDA of our plans to move each patient due to the investigational designation of the EXCOR pediatric VAD in the United States at the time of transport. The transport team consisted of a pediatric cardiac intensivist, pediatric critical care transport nurse, pediatric transport respiratory therapist, and two bioengineers. During transport, two Ikus drivers were always present with the patient for safety (in case of driver failure) and to facilitate moving the patient between each vehicle (described later).
Ambulance transportation presented a unique set of challenges. During a preparatory meeting before the transport, we discovered that the large ambulances we had reserved (typically for ECMO patients) were too small to safely accommodate the patient, both of the Ikus drivers, medical equipment, and personnel. We therefore reserved two ambulances (each containing at least a 4,500 W inverter) for each leg of the trip. For both patients, we found the pump tubing (tethered to the Ikus) to be too short to allow for a stepwise loading of the patient/stretcher and the Ikus; it was also impossible to load both components simultaneously. Our process for loading patients into the ambulance was the following: 1) to secure the backup driver in the ambulance with it pumping at the patient’s current settings against the Berlin Heart tank units; 2) to move the stretcher to the loading position at the back of the ambulance, with the primary driver along side of the stretcher; 3) a bioengineer/nurse on the ground disconnects the pump from the primary driver and initiates hand pumping while the patient is partially loaded into the ambulance; and 4) the hand pump is then transferred to another engineer/nurse in the ambulance, who continues support until the stretcher reaches the back of the ambulance and the pump(s) is able to be plugged into the backup driver. The driver remaining on the ground then becomes the backup driver. Each driver was located near the front of each respective ambulance and anchored with ratcheting nylon straps. Three people were required to lift each driver into and out of the ambulances.
Air ambulance loading and unloading was dependent on the equipment available at each location as most airports were not equipped to handle our unique situation. For the intubated patient, at both airports, we were able to safely secure the patient and the pump driver to a metal board attached to an industrial lift that could reach the cargo bay on the side of the aircraft. The nonintubated patient (who also had substantially less intravenous medications) was carried by her mother down the aircraft stairs while being hand pumped by a bioengineer and was reconnected to an Ikus driver waiting on the ground. Despite the challenges in transferring each of these patients between vehicles, no adverse events were noted during either transport.
Of the eight different ambulances used during the two transports, three had power fuses trip when the Ikus driver was actively supporting a patient. Two of the instances occurred before departure in the ambulance, and we were able to transfer the patient to an alternate ambulance. However, the third power failure was en route from the referring hospital to the airport, requiring battery support for 30 min. We used two external battery supplies to conserve driver battery power; however, each external battery only lasted approximately 6 min.
There are several possible explanations for the power fuse trip phenomenon. The requirements for the Ikus are a sinusoidal voltage of 115 V AC at 60 Hz, a peak power of 1,000 W, and a continuous output of 600 W. Many ambulance inverters provide rectangular, trapezoidal, or “quasi-sine” voltages that may cause disturbance in highly sensitive equipment such as the Ikus; however, every ambulance was able to initially meet the driver power requirements, suggesting that this may be an unlikely source of the problem. The fuse on an ambulance inverter typically has a much higher rating than the fuse on an Ikus but only the inverter fuses tripped. Given the power rating of the inverters, it is unlikely that they could not provide sufficient power to the Ikus; rather, they may not have been able to meet the peak current requirements if sufficiently large current spikes were present. The Ikus may require as much as 10 times the peak current for milliseconds (Berlin Heart technicians, personal communication); if an inverter is equipped with a short duration fuse, this fuse may be tripped even though the current requirement could have been met over a longer period of time. One potential remedy to this problem is to change the fuse of the inverter to trip at a slower rate (i.e., 2 sec if the spike duration is milliseconds); however, this is unlikely as the fuse is usually standardized to the inverter for other nominal requirements. A more practical solution might be to bring a commercially available power conditioning unit for use between the inverter and the driver to supply extra current during spikes and filter the current spikes from the inverter. An additional consideration of this problem is that the Ikus driver was designed as a stationary unit to be used in a hospital setting; our transportation of these patients was considered off-label use and should not be interpreted as a critique of the manufacturer’s design.
Although previous reports have described protocols and challenges for transporting adult patients supported with a VAD, there are few reports of transportation of VAD patients ≤18 years of age. Matsuwaka et al.14 report the fixed-wing transport of an 18-year-old male Toyobo (Toyobo, Osaka, Japan) LVAD patient from Osaka, Japan, to Houston, TX. Cultural obstacles to obtain a donor heart necessitated the transfer of this patient to the United States, where he received a donor organ after 13 months of support. Before transport, the VAD was tested at different atmospheric pressures to validate proper function, of which there was no noticeable change. There were also no problems in pump performance noted during the actual flight. Owens et al.15 described the emergent helicopter transfer of a biventricularly supported 15-year-old Thoratec Pneumatic (Thoratec Corp, Pleasanton, CA) VAD patient. The adolescent patient was safely transferred during hurricane Katrina, despite additional complex medical support and challenges providing power (gas generator) and movement of the large pneumatic driver (180 kg). In addition, Tissot et al.7 report the only case study involving the transport of a patient supported by the Berlin Heart EXCOR VAD. A 13-year-old female patient touring France experienced cardiogenic shock, necessitating ECMO support and eventually implantation of an 80 ml EXCOR LVAD. The patient was transported from Marseilles, France, to Denver, CO, and was transplanted 3 months later. In each of these three case studies, an adolescent was supported using a long-term adult VAD. Although each presented unique challenges for the patient and transport team, only the Tissot report is similar to our experience because it involves the EXCOR VAD. However, this patient was able to use the Berlin Heart mobile driving unit (instead of the Ikus stationary driving unit) for the transport, greatly simplifying the transfer process as the mobile unit is designed for improving patient movement. As stated previously, the mobile driving unit is not an option for pediatric patients as it only supports the 50, 60, and 80 ml pumps. In addition, the Tissot patient was able to walk on her own, allowing her to board and exit the ground and air ambulances via stairs while the transport crew carried the mobile driver. This also was not an option during our transport.
Extracorporeal membrane oxygenation remains an alternative method for nontransplanting centers to provide temporary mechanical circulatory support for pediatric heart failure patients until transfer is arranged to a transplanting institution. The experienced receiving institution would then have the option of leaving the patient on ECMO support or implanting the EXCOR pediatric VAD. Although performed at only select centers, transportation of pediatric patients supported by ECMO has been described in the literature with generally positive results.16–19 Heulitt et al.16 described a mobile ECMO circuit designed by their institution for transporting small children, allowing for ECMO to be initiated at the referring center instead of waiting until arrival at the receiving institution. This article was updated in a report by Clement et al.,17 which describes long-term patient outcomes and modifications to the mobile ECMO circuit into two separate systems to accommodate neonates or larger children. A similar mobile ECMO circuit is also presented by Coppola et al.18 In each article, the authors report that no patient mortality occurred during the transport process. However, there were several instances of mechanical adverse events such as oxygenator failure, power supply interruption, and tubing leaks.
Extracorporeal membrane oxygenation may be an attractive option for low-volume centers as it is typically a simpler procedure compared with VAD implantation. However, Fraser et al.1 reported that pediatric cardiac failure patients implanted with the EXCOR pediatric VAD had better outcomes and nearly half the adverse events than patients implanted with ECMO. For patients only experiencing cardiac failure, VAD support may be the preferred treatment option, but decision making will certainly be dictated by the capabilities of each center. It is the opinion of the authors that the most appropriate means of support should take into consideration the presentation of the patient, capabilities of the treating institution, and optimally with preexisting coordination between the referring institution and the receiving transplant center. We believe that the increased availability of this technology, coupled with longer support times, may lead to an increase in the movement and transportation of pediatric patients supported with the EXCOR pediatric VAD device and present our experience on how to accomplish this safely given the obstacles faced.
We demonstrated the safe and effective transportation of two pediatric patients implanted with Berlin Heart EXCOR pediatric VADs and maintained on the Ikus stationary driver. A team consisting of a pediatric cardiac intensivist, pediatric critical care transport nurse, pediatric transport respiratory therapist, and two bioengineers was critical to our success with both transports. We experienced problems maintaining power to the Ikus drivers in several ambulances, which may be resolved with the use of a power conditioning unit.
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heart-assist device; extracorporeal circulation; heart transplantation; pediatrics; air ambulances; transportation of patients