The (Sound) Wave of the Future
When talk turns to the use of ultrasound technology, the back of an ambulance isn't usually the first venue that springs to mind--especially if you've ever tried to take a blood pressure while traveling down a pothole-riddled city street or a bumpy country road. But actually, it's not as far-fetched as it may seem. Ultrasound, though not used widely by American EMS, can be a benefit to providing care in the field.
Ultrasound (sound above the level of human hearing) units send waves out to interact with something and then read the resulting echo that bounces back when these waves encounter an obstacle. If a wave fails to hit anything, it scatters and dissipates. If it hits something and bounces back, an image is produced. Since most of the human body is composed of either solid or liquid matter (except for the thorax, which is mostly air), this technology can produce useful, non-invasive images of the body's internal structures.
Because the pictures are produced by sound waves, distortion due to movement is reduced. The quality of ultrasound images acquired in an ambulance or helicopter is on par with those taken in an emergency department. This tool has the potential to be helpful in medical (e.g., measuring cardiac output) and traumatic (e.g., identifying intra-abdominal bleeding) emergencies, both in regard to actual interventions in the field as well as allowing ED physicians to prepare adequately for patients with problems identified or confirmed via ultrasound.
Although ultrasound imaging has been introduced into the prehospital arena in Europe during the past two decades (including the Frankfurt Fire Department in Germany and the helicopter arm of the London Ambulance Service) and its use has been supported by rigorous studies, acceptance of field ultrasound has been slow to come to the United States.
The Odessa Experience
Among the few EMS agencies in the U.S. currently utilizing this technology is the Odessa (TX) Fire Department (OFD). The system has been utilizing ultrasound technology since May 2000, with exceptional results.
OFD EMS units cover an area of 904 square miles with a sparse population of 124,000 (roughly 14 people per square mile). The devices they employ are manufactured by SonoSite and are part of its 180 series. At just a tad over five pounds each, they are priced similarly to high-end cardiac monitors.
According to OFD EMS Medical Director David Spear, MD, FACEP, the initial training for personnel lasts between 6--8 hours. Paramedics are instructed on topics such as verification of cardiac motion, ascertaining pregnancy and determining if there is blood in the abdominal cavity. They are also cautioned that "false positive" and "false negative" results are possible. For instance, a false positive can mean fluid is present, but is not blood; a false negative can result if there is blood, but not enough to detect. A volume of 500cc--1,000cc of blood is needed to be distinguishable on an ultrasound scan.
As part of the operating protocols established by Spear, OFD paramedics are directed to complete ultrasound scans on patients with specific presenting problems or complaints (penetrating trauma, chest pain, abdominal pain for female patients of child-bearing age, etc.). The goal for these prehospital providers is not to complete an abdominal or thoracic ultrasound as a hospital radiologist would want done. Rather, it is to use this tool to confirm what may already be suspected based on their assessment of mechanism of injury, nature of illness and physician exam. If a blunt-trauma patient is hypotensive, for instance, then an ultrasound screening exam is done to look for suspected blood in the abdomen.
The images acquired are saved onto a Sony GVD 1000 and presented to the ED physician receiving the patients. Since the program began in 2000, OFD paramedics have scanned scores of patients and have detected and examined heart attacks, abdominal injuries and fetal conditions. They even have recorded images of an arrested heart regaining its motion with the help of a pacemaker. Spear stresses that one of the golden rules of ultrasound utilization by OFD is that the medics never delay patient care or transport because of ultrasound use, and that the devices are used as an element of the secondary survey while transporting. Quality improvement (QI) review of calls where ultrasound is utilized is simplified by the fact that the vast majority of the patients transported by OFD go to one hospital--Medical Center Hospital of Odessa. With this almost-seamless link from the field to the ED available, Spear also reports that OFD is gearing up to begin a randomized study of numerous variables associated with the prehospital utilization of ultrasound.
The ability to detect various life-threatening conditions (both medical and traumatic) in the field may challenge traditional algorithms for prehospital care and significantly impact EMS. Yet, despite the positive impact to patient care experienced in Odessa, any indication that ultrasound scanning will be implemented more widely, even in the state of Texas, remains elusive. Trauma patients in urban and most suburban areas can be quickly taken to full-service facilities within respectable response-time parameters. Since the ultrasound scan is completed in the secondary survey, by the time an image is acquired and the information transmitted, most patients in those systems are already at hospitals.
In the United States, the future of ultrasound utilization by EMS may lie in the nation's rural areas, where transport times to stabilizing facilities can be an hour--or hours--long. Having this advanced technology, and with it the ability to discern severe underlying problems in both trauma and medical patients, may be a logical next step for many rural EMS agencies.
Raphael M. Barishansky, MPH, is chief of public health emergency preparedness for Prince George's County (MD) Health Department. A frequent contributor to and editorial advisory board member for EMS World, he can be reached at firstname.lastname@example.org.