Special Delivery: Mobile Stroke Unit Brings CT Imaging to the Streets of Memphis
By Kathy Hardy
Vol. 17 No. 11 P. 10
Mobile, meaning able to move freely or easily, isn't an attribute typically used to describe something that weighs more than 14 tons. However, a multidisciplinary team of neurology and imaging professionals navigating the old and narrow streets of Memphis in a medically equipped truck is redefining the word with a first-of-its-kind mobile stroke unit that includes a 2-ton, hospital-strength, hospital-caliber Siemens Healthineers Somatom Scope CT scanner onboard.
Launched this summer by the University of Tennessee (UT) Health Science Center at Memphis College of Medicine, this mobile apparatus and its team of stroke care–trained medical professionals and first responders is making inroads in the rapid treatment of stroke patients, taking minutes off the time between diagnosis and treatment. While this is the fifth such mobile unit in the United States—the world's first unit hit the road in Germany in 2011—the UT Memphis truck's capabilities make it a world leader.
"This is the first mobile stroke unit to bring a hospital-quality, 16-slice CT scanner to the front yards of stroke victims," says Anne W. Alexandrov, PhD, RN, CCRN, NVRN-BC, ANVP-BC, AGACNP-BC, FAAN, a professor with the UT Health Science Center and chief nurse practitioner for the mobile stroke unit. "We can diagnose and begin treatment, including alteplase tPA [the blood clot–busting tissue plasminogen activator], within the critical first minutes from the time 911 was called, before arriving at the hospital."
Covering New Ground
The goal when designing the UT Memphis mobile stroke unit was to minimize morbidity and mortality and to have more patients leave the hospital fully functional. Without the mobile unit, Alexandrov says it would take about 20 minutes just to transport the patient to the hospital. Upon arrival at the emergency department (ED), it can take up to another 25 minutes before the patient receives a CT scan. She says another five to 20 minutes can pass before the scan is read, with time for tPA treatment still to follow.
"The UT Memphis mobile stroke unit patients can go directly to the catheterization lab, neuro intensive care unit, or hospital stroke unit, bypassing the emergency department entirely," she says.
The first steps worldwide in moving stroke treatment from the ED to a prehospital setting occurred in Homberg and Berlin, Germany. In those cases, a CT scanner was placed on an ambulance, along with either onboard or remote stroke expertise, as well as point-of-care lab testing. The first mobile units in the United States, launched in Houston and Cleveland in 2014, utilize head-only, portable, 8-slice CT scanners, as do the mobile units in Germany.
Where the UT Memphis mobile stroke unit breaks ground is in its use of a hospital-quality, full-body, 16-slice CT scanner with angiography (CTA) imaging that provides rapid brain and vascular imaging. The UT Memphis mobile unit's CT scanner is equipped with a dedicated gantry that automatically repositions the patient as needed to obtain images; it also provides the same number of slices, in high resolution, as would be obtained in a hospital setting.
"With the UT Memphis mobile stroke unit, we can have the definitive diagnosis complete within seven minutes," Alexandrov says. "We can complete CT/CTA scans in three to four minutes total time, and the images we get are high resolution, just as we would see in the hospital, so there is no need to repeat scanning/radiation exposure because of image quality."
The UT Memphis mobile stroke unit serves a 10-mile radius around Memphis, responding when notified by the city's fire dispatch system following a 911 call that refers to stroke or symptoms that have the characteristics of stroke. Alexandrov says they respond along with an EMT or paramedic unit. Once on the scene, the patient is assessed and moved into the truck, if it's determined that he or she is experiencing a stroke. Before imaging can take place, however, she says there is a logistical issue that needs to be addressed.
"The truck needs to be leveled for the CT scan," she says. "The truck has stabilizers that can lift the front end of the truck, if necessary. This process is managed by our CT tech and advanced emergency medical tech and is under way while the nurse practitioner and paramedic are assessing the patient on the scene, before moving them into the truck."
Once the truck is level, all members of the rescue team and the CT technologist rapidly position the patient on the scanning table. Time is then of the essence, with CT scanning beginning within three or four minutes of arrival at the scene, on average. Images are quickly read and the patient is diagnosed. If stroke is confirmed, and the patient meets criteria for treatment, then the patient's blood pressure is controlled with a Cardene infusion and alteplase tPA is started, which Alexandrov says can be done while the truck is en route to the hospital. The UT Memphis mobile stroke unit program currently has a 27% alteplase tPA treatment rate, higher than most US stroke centers.
Smaller Footprint, Big Step
The vision for the UT Memphis mobile stroke unit began two years ago, when the hospital approached Malvern, Pennsylvania's Siemens Healthineers about working with them on creating this state-of-the-art technology on wheels. The company had just launched its 16-slice Somatom Scope CT scanner, a device designed for medical facilities looking to cost-effectively create high-quality images while filling a smaller footprint. The scanner is "small enough to fit in a closet," or, in this case, the back of a large truck.
"This is Siemens Healthineers' first mobile stroke unit," says Dena Cunningham, CT product manager for neuroradiology and the ED at Siemens Healthcare. "We worked closely with the UT Memphis College of Medicine to create a full unit on wheels, with a table in the unit. We even worked to create a customized, small, lead-shielded door inside the truck to shield the CT technologist from radiation while imaging is underway. Typically, people would have to step off the truck to avoid radiation exposure. We figured out how to make the door work in a small space."
Other customizations to make the CT scanner fit in the truck include a modification of the scan range from the aortic arch to the patient's head, Cunningham says.
Mark Palacio, Siemens Healthineers' product marketing manager for the Somatom Scope CT system, says the UT mobile stroke unit includes an internal power source—lithium batteries—capable of matching a regular electrical outlet's power supply.
"They can complete multiple scans off one charge," he says.
There's also a separate charging system for the CT components on the ambulance that differs from the routine ambulance charging system, Palacio adds. And, because of the Somatom Scope's smaller size and extremely low power consumption requirements, the CT takes advantage of air cooling, meaning that there is no need for large cooling systems or chillers, he says.
"This works well on the truck, where there just isn't space for a large cooling apparatus," he says.
A conservative eye to space allows for a four-person team that takes to the streets when a 911 call comes in with details regarding a potential stroke victim. Each shift on the mobile unit includes a nurse practitioner, a CT technologist, an EMT, and a paramedic, all trained in stroke treatment. The unit is staffed with stroke fellowship–trained, doctorally educated nurses certified as advanced neurovascular practitioners (ANVP-BC). In addition, UT Health Science Center neurology department chair Andrei V. Alexandrov, MD—Anne Alexandrov's husband—often joins the crew on the road. He says that his work in the field is no different from his work in the hospital. It's the patient who experiences the difference.
"Working in the mobile setting offers us unprecedented patient contact, enabling us to decrease the time from diagnosis to treatment," Andrei Alexandrov says. "We are giving tPA in the field for the first time in Memphis, and this gives the patient a greater chance of survival and successful recovery."
It takes a certain type of medical professional to join a unit like this. UT Medical Center CT Technologist Jordan Sanders never imagined that, after more than two years in her hospital role, she would be hopping in a large rescue truck and racing into emergency situations.
"Going from the hospital to the mobile unit doesn't change the details of my job," Sanders says. "I still follow the same CT scan protocols. What's different, however, is that I get the see the entire stroke treatment process, not just the diagnosis aspect."
A new member of the unit's crew is Wendy Dusenbury, DNP, APRN, FNP-BC, CNRN, ANVP-BC, an assistant professor in the School of Nursing at Wichita State University in Kansas. Dusenbury was invited to join the inaugural group of practitioners at UT Memphis to work with the mobile stroke unit, completing her first shift in August. She spends one week every month in Memphis, making runs with the team. She learned about the unit while obtaining her neurovascular training and certification and was familiar with the work of Anne Alexandrov, who chaired Dusenbury's doctoral project.
"Acute treatment and management is my favorite part of stroke care," Dusenbury says. "With my background in neurologic ICU, I jumped at the opportunity to be a part of this type of work."
She sees benefits in the mobile unit not only in saving time but also in the way treatment within the unit is focused on just one area—stroke treatment.
"On the mobile unit, we're able to do what we need to do without any distractions," Dusenbury says. "We can take the patient to the emergency department with the acute work already completed. That enables hospital personnel to begin dealing with the next steps for that patient."
Need Outpaces Reimbursement
As with many new, leading-edge medical services, widespread utilization of mobile stroke units doesn't come without challenges; in this case, it's reimbursement. Anne Alexandrov explains that, at present, drugs such as the clot-buster alteplase tPA and the blood pressure reducing calcium channel blockers Cardene or Clevidipine, along with CT and CTA scans, are not being reimbursed by the Centers for Medicare & Medicaid Services when used in prehospital settings, such as the mobile stroke unit.
"We are currently working with legislators to develop new laws that will encompass these tests and treatments," she says. "Ambulances are only able to charge for [advanced life support] fees that deal with different levels of advanced life support provided prior to hospitalization, with the assumption that definitive diagnosis and treatment only happens in the hospital setting. Private insurers could certainly be billed for these things, but, while some may pay, others may not.
"This field is clearly growing more rapidly than the current reimbursement system," she adds. "And, since mobile stroke units have the ability to dramatically decrease disability and death from stroke due to initiation of ultraearly treatment, it's imperative that this care be reimbursed so that other programs are well situated to support their communities."
Data gathering regarding patient outcomes will help in reimbursement efforts, Dusenbury says, particularly as the mobile stroke unit serves a community greatly in need of advanced stroke care. Memphis is located in the heart of what the Heart Attack and Stroke Prevention Center calls "the Stroke Belt," an 11-state region of the United States, predominantly southern states, where studies show that a risk of stroke is 34% higher for the general population than it is in other areas of the country. Researchers believe that higher-than-average rates of obesity, smoking, and high blood pressure in the Stroke Belt account for the increased risk of death from cardiovascular disease there. In addition, the Centers for Disease Control and Prevention notes that Shelby County, which includes Memphis, has a stroke rate per 100,000 people that is 37% higher than the national average.
"There are 1.3 million people living in [the greater metropolitan area of] Memphis, where there is a high incidence of stroke," Andrei Alexandrov says. "With the mobile stroke unit, we're able to reach these high-risk patients, diagnose them, and treat them with tPA within a time window where we are most likely to see positive results."
Given the scope of the need for acute stroke treatment in the region, Cunningham praises the efforts of the UT Memphis staff in making this mobile unit a reality.
"They're extremely passionate about making this work in the community," Cunningham says. She adds, "We never thought we'd see our mobile CT scanner in an ambulance like this."
Note: As this issue was going to press, NewYork-Presbyterian Hospital announced the launch of the first mobile stroke unit on the East Coast.
— Kathy Hardy is a freelance writer based in Phoenixville, Pennsylvania. She is a frequent contributor to Radiology Today.