Ultrasound in emergency medicine
Portable Ultrasound for Remote Environments, Part I: Feasibility of Field Deployment

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Abstract

Background: In field medical operations, rapid diagnosis and triage of seriously injured patients is critical. With significant bulk and cost constraints placed on all equipment, it is important that any medical devices deployed in the field demonstrate high utility, durability, and ease of use. When medical ultrasound was first used in patient care, machine cost, bulk, and steep learning curves prevented use outside of the radiology department. Now, lightweight portable ultrasound is widely employed at the bedside by emergency physicians. The techniques and equipment have recently been extrapolated out of the hospital setting in a wide variety of environments in an effort to increase diagnostic accuracy in the field. Objectives: In this review, deployment of lightweight portable ultrasound in the field (by emergency medical services, military operations, disaster relief, medical missions, and expeditions to austere environments) is examined. The feasibility of field deployment and experiences of clinicians using ultrasound in a host of environments are detailed. In addition, special technological considerations such as telemedicine and machine characteristics are reviewed. Conclusions: The use of lightweight portable ultrasound shows great promise in augmenting clinical assessment for field medical operations. Although the feasibility of the technology has been demonstrated in certain medical and trauma applications, further research is needed to determine the utility of ultrasound use for medical illness in the field.

Introduction

Although sonar was first used during World War I, medical ultrasound was not available until the 1960s, and then only in the form of static images. From the late 1970s to early 1980s, medical ultrasound technology evolved to allow for real-time dynamic scanning, but large machine size limited its utility (1). In 1996, the Defense Advanced Research Project Administration awarded a grant for the development of a highly portable ultrasound device for use in battlefield applications. SonoSight (now SonoSite, Inc., Bothell, WA) collaborated with VLSI Technology, Harris Semiconductor, and the University of Washington's Applied Physics Laboratory and School of Medicine to prototype one of the first handheld ultrasound devices for field military use (2). By the late 1990s, several companies began manufacturing portable machines for civilian use. Many weighed < 6 pounds, allowing for new applications of a technology previously locked within radiology departments.

Current portable ultrasound machines are lightweight, utilize high-end microprocessors for imaging software, provide high image quality, offer multiple modes (including color Doppler, vascular, echocardiography, and endovaginal examinations), and are built to withstand abusive environmental conditions. For urgent medical applications, these machines compare well to the traditional and much larger machines found in radiology departments, and are accurate when compared to other gold standards such as computed tomography (CT) scan or operative findings. Table 1 highlights a range of studies comparing the performance of portable ultrasound devices to gold-standard diagnostic modalities (3, 4, 5, 6, 7, 8, 9, 10, 11). Market demand has greatly contributed to their evolution so that many of the portable machines now available have far more application, utility, and durability for emergency use than their traditional counterparts, at vastly reduced costs.

Non-radiologist experience in hospital settings and increased portability of ultrasound machines has led to increased use of the technology outside of the hospital. Physicians, military medics, and emergency medical services (EMS) personnel have used portable ultrasound machines successfully in the field to diagnose conditions such as pleural, peritoneal, and pericardial effusion and deep venous thrombosis (12, 13, 14). Table 2 highlights studies of ultrasound deployment in austere or prehospital environments (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25). The clinical scenarios and patterns of injury found in these environments vary widely. However, there is a common thread of rapid assessment with a rugged, portable technology used as an adjunct to the standard physical examination tools such as the stethoscope.

It is important that any equipment carried to a remote area be lightweight and rugged. In a study of ultrasound use during helicopter transport, no mechanical problems were encountered during a 1-year study period with 100 patients assessed (22). When used in military operations in Iraq, lightweight portable ultrasound was found to be useful in assessing trauma patients. In one study, a portable device was used over a 2-month period in conditions of high ambient light and temperature. Fourteen negative cases (confirmed by repeat examinations and observation or laparotomy) and one positive case (confirmed by laparotomy) of intraperitoneal fluid were detected (26). The authors noted the importance of small size, maneuverability, and the option for battery power in the space constraints of a mobile field hospital. Some degradation in expected battery life was noted, and attributed to storage in high temperatures during summer months. Another study from a mobile Combat Support Hospital (CSH) in Iraq described 400 ultrasound scans performed using a handheld unit during the first 6 months of operations (27). Focused assessment with sonography in trauma (FAST), renal, and a wide range of other scans were performed. The authors noted that the scans improved their diagnostic capacity and helped prevent unnecessary evacuation to higher-level facilities out of theater solely for radiologic imaging. In a recent case report of a ruptured ectopic pregnancy diagnosed in a field hospital setting with portable ultrasound, the authors subjectively described good image quality and durability throughout the deployment of the device (28). The device in this study was exposed to heat, wind, and sand, and the authors report that it was well suited to use in a field hospital or during transport. Portable ultrasound was incorporated into a CSH deployed in Afghanistan over a 21-month period (29). In this setup, radiologic equipment consisted of a digital plain film system, two portable handheld ultrasound units, and a CT scanner. The primary uses of ultrasound described were for unstable blunt trauma patients, screening non-acute abdominal complaints, female pelvis, and foreign body cases.

When deployed on a medical expedition to remote Amazon jungle settlements, portable ultrasound improved diagnostic capacity beyond physical examination alone (18). Data were collected over two separate 2-week visits. Of 25 ultrasounds performed for suspected hemoperitoneum, abdominal aortic aneurysm, infection, and other indications, disposition was altered due to the scans in seven cases. Batteries were the only means of power for the device due to lack of electricity. The device was used at altitudes up to 5182 m, as well as sea level. Further evidence of the utility of ultrasound at high altitude was demonstrated in Nepal, where thoracic and ocular ultrasound assessments were performed at 4240 m (24). Portable ultrasound has also been used as part of the medical support for expedition teams on Mount Everest, through the Canadian Everest Medical Operations Team (30).

The most remote experience with portable ultrasound to date has been on board the International Space Station. In this setting, crew with limited medical training must make rapid decisions, fettered by technological constraints on machine power requirements and interference. The impact of an injured crew member is great, and this setting highlights the importance of rapid diagnosis of injury and illness. Thus, ultrasound remains the only imaging modality available in this environment (19).

In 2001, an editorial summarized the range of experience with portable ultrasound in remote settings at the time. Several case reports were cited, but little evidence existed at that time to suggest that the portability, durability, and cost of the machines would be outweighed by their potential utility (31). In the past few years, the range of experience with remote applications for sonography has continued to increase at a remarkable rate, a trend that mirrors improvements in the technology itself. By 2008, the American College of Emergency Physicians described portable ultrasound use in remote environments among the indications in the scope of practice of emergency physicians (32).

The remainder of this review will summarize current evidence for the use of ultrasound applications in austere or remote settings to predict future directions for outcome-based research. Although ultrasound equipment has dramatically improved in its quality and portability, the decision to add another piece of equipment to an expedition is often offset by weight, price, and prior evidence of usefulness.

As communication technology improves, remote transmission of images to centralized medical decision zones has been investigated as a substitute for traditional models of medical manpower, where the imager and physician are the same person. In the case of the International Space Station, for example, continuous duty by a generalist physician-astronaut has been less feasible than training astronauts how to acquire and downlink ultrasound images at the direction of designated medical control ground staff.

For over a decade, dynamic echocardiography images have been transmitted for real-time cardiologist interpretation by standard telephone modems as well as by radio satellite transmissions (33, 34). In the latter study, images were obtained at a military combat-support field hospital and transmitted from the ultrasound machine to the satellite using a wireless radio transmitter contained in a tactical vest. A similar setup was tested by the U.S. Army Support Hospital for use on a moving ambulance, and the “roaming vest” transmission method provided adequate and interpretable images to be transmitted remotely (35).

A tele-ultrasound system was devised for the National Taiwan University Hospital EMS system as well (36). Investigators in this study used a 3G communication protocol to transfer data (e.g., ultrasound images, video, vital signs) from the ambulance to the dispatch and mission control center as well as the receiving hospital emergency department. Thus, ultrasound images obtained in the ambulance can be reviewed remotely by clinicians in a variety of locations. The authors noted that cellular transmission is limited by network availability and may not be suitable for all geographic areas.

More recently, medical control for the Mount Everest expedition has included a variety of integrated telemedicine applications (30). Portable ultrasound devices are used on-mountain by the medical team, and images and video clips of ultrasound and other data (such as heart monitors) are transmitted to a computer onsite via local area network. The computer then transmits medical data and ultrasound imaging from Mt. Everest to the Payload Tele-operation Centre at the Canadian Science Administration via satellite. This allows for remote viewing by clinicians at participating institutions such as the University of Ottawa Heart Institute in Canada and Henry Ford Hospital in Detroit, MI. This information can be used to provide medical control to non-physicians on mountain in real time. Such real-time guidance may decrease the initial training time and learning curve for onsite providers, as ultrasound image acquisition can be assisted (and images may be interpreted) by experts remotely. This “train-as-you-go” model is also employed aboard the International Space Station, and may have dramatic ramifications for military deployment. Thus, medics with general training can augment their skill set to rapidly adapt to new situations utilizing remote assistance and image interpretation.

Ultrasound has been used extensively in less economically developed countries, and the World Health Organization (WHO) has recommended its inclusion as a diagnostic modality for decades. Three levels of imaging systems were described in a 1990 WHO report, from Level I (most basic versions of X-ray, ultrasound, CT) to Level III (most comprehensive equipment, capable of sophisticated imaging such as Doppler ultrasound, angiography, magnetic resonance imaging) (37). In 1998, the WHO detailed standards in ultrasound training and implementation worldwide, where the technology could be applied at all three levels of imaging system implementation (38). A growing number of case reports and series have demonstrated potential utility in this setting when other technologies are either too expensive or require too much ongoing maintenance. In response to a lack of ultrasound training programs in developing nations, the WHO published the Manual of Diagnostic Ultrasound in 1995 (39). It was intended for use by physicians, sonographers, nurses, and other health care providers working with a basic ultrasound scanner. Thus, there is growing international support for the use of bedside ultrasound technology in the care of patients in areas with limited medical resources.

An early study of the utility of ultrasound as an adjunct to physical examination was carried out in 1991–1993 in a rural hospital in western Cameroon with a donated ultrasound device. In 323 cases where a gold standard was available, ultrasound provided the diagnosis in 31.6% of the cases, confirmed a prior diagnosis or excluded alternate diagnoses in 36.2% of the cases, had no influence on the diagnosis in 27.6% of cases, and was incorrect in 4.6% of the cases (40).

Recently, investigators reported their experience introducing portable ultrasound into the health services of a refugee camp in rural Tanzania (41). Four physicians and six clinical officers were trained in the use of ultrasound through an intensive 4-day course. A portable ultrasound device was used in the camp to assist in patient care for a 2-year period. There were 547 ultrasound scans recorded for 460 patients during the study period, including abdominal, pelvic, renal, cardiac, soft tissue, and other applications. About two-thirds of all studies performed in the course of clinical care were gravid pelvic (24.1%), non-right upper quadrant abdominal (22.7%), and non-gravid pelvic scans (21.9%). The practitioners reported subjectively finding ultrasound especially useful in determining pregnancy and pregnancy complications, suited to an area with a high maternal mortality rate.

Two studies examined the use of portable ultrasound in rural Rwanda in 2008. A 9-week curriculum on obstetrics, abdominal hepatobiliary, and other indications was administered at two rural hospitals after a needs assessment determined the highest-yield areas on which to focus training (42). An ultrasound coordinator was established at each site to be the lead physician caring for the ultrasound machine, ordering supplies, and maintaining the ultrasound logbooks and ongoing quality assurance. Clinical studies during the 10-week post-training period were conducted using portable machines. A total of 242 patients underwent scanning during that time (43). Obstetrical ultrasound (including estimation of gestational age, determination of fetal life, and evaluating placental abnormalities) was the most common indication for scanning. Abdominal, cardiac, and thoracic applications were utilized as well. Ultrasound altered initial patient management in 43% of cases. Most commonly, it directed clinicians to perform a surgical procedure (such as cesarean section, biopsy, or dilatation and curettage for retained products of conception) based on the results. Clinicians regularly e-mail scans to the study team for ongoing quality assurance after the initial study period, and the clinicians staffing these resource-poor rural practices have sustained the ultrasound programs without on-site intervention by foreign study team members.

A portable ultrasound system was deployed in a variety of settings in rural Ghana to assess its utility as a diagnostic aid (44). Medical providers used the machine in two rural clinics as well as medical offices and a hospital operating room in the region. Over a 1-month period, 67 sonograms were performed. Eighty-one percent of ultrasounds were abnormal, including findings such as biloma, breast neoplasm, intrauterine fetal demise, Legg-Calvé-Perthes disease, ascites, and others. Eighty-one percent of ultrasounds were determined to add to the clinical diagnosis, and 40% had the potential to influence outcome or a decision regarding treatment.

The use of ultrasound in the field has been made possible by lightweight, portable devices capable of being transported easily. Continued improvement in device technology may open even more opportunities for clinical decision-making. There are a few major areas of improvement that would make ultrasound devices even more suited to field operations.

First, machine weight, bulk, and cost must continue to decrease. As miniaturization of parts such as batteries, screens, and processing units proceeds across many types of devices, the possibility of smaller, lighter, less expensive machines should be realized. Next, machines must be able to withstand extremes of temperature and maintain a reasonable battery life with low risk of processor overheating. Image quality continues to improve across many vendor platforms, and displays that provide adequate images in high ambient light conditions are necessary.

As always, ease of use is paramount. Rapid “boot-up” times and simplified controls will aid clinicians in incorporating ultrasound into real-time decision-making. The capacity for image storage and remote transmission will allow providers in the field to interface with others at more central locations. This is especially important as telemedicine is being incorporated into many disaster, EMS, and military operations.

Whereas device advancements have improved the field of ultrasound greatly, so too has the progression of research in the last few decades. Early case reports were followed by observational studies, and now some outcomes-based research has been reported. A number of studies have demonstrated the feasibility of ultrasound deployment in the field. Future research focused on patient-centered outcomes such as time to diagnosis and treatment, and timely deployment of appropriate resources will advance this burgeoning field. The next installment of this review will cover the major indications for field use of ultrasound, literature to support their use, and cutting edge uses that have only begun to be explored.

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