TY - JOUR
AU - MC, Paul F. Crawford, USAF
AB - ABSTRACT In the last 10 years, the use of ultrasound has expanded because of its portability, safety, real-time image display, and rapid data collection. Simultaneously, more people are going into the backcountry for enjoyment and employment. Increased deployment for the military and demand for remote medicine services have led to innovative use and study of ultrasound in extreme and austere environments. Ultrasound is effective to rapidly assess patients during triage and evacuation decision making. It is clinically useful for assessment of pneumothorax, pericardial effusion, blunt abdominal trauma, musculoskeletal trauma, high-altitude pulmonary edema, ocular injury, and obstetrics, whereas acute mountain sickness and stroke are perhaps still best evaluated on clinical grounds. Ultrasound performs well in the diverse environments of space, swamp, jungle, mountain, and desert. Although some training is necessary to capture and interpret images, real-time evaluation with video streaming is expected to get easier and cheaper as global communications improve. Although ultrasound is not useful in every situation, it can be a worthwhile tool in the austere or deployed environment. INTRODUCTION Increased U.S. military operations tempo has increased demand for medical providers to “do more with less” in austere and deployed environments. Clinicians often find themselves in uncomfortable locations treating patients with minimal and makeshift supplies. Since laboratory and radiology services are often very limited in these situations, clinical judgment becomes more important when deciding which patients need medical evacuation. However, published studies point out the ease and utility by which ultrasound can be employed in austere settings. This review will detail the evidence that ultrasound is useful in a rapidly increasing number of situations. HISTORY AND OVERVIEW SONAR, the first use of ultrasound, was developed during World War I, and ultrasound was found to have medical uses in the 1940s.1 Ultrasound uses cyclical, high-frequency sound waves that are well above the threshold of human hearing (normally 20,000 Hz) created by an electrical current into a ceramic transducer thus producing a piezoelectric effect that creates a sound wave. Lower range frequencies, in the 2 to 7 MHz range, have high penetration but low resolution. These frequencies are often best for deep locations such as the abdomen, pelvis, and heart.1,2 Higher frequencies, 8 to 12 MHz, offer low penetration but give impressive resolution. These frequencies are often used for musculoskeletal examinations, “small parts” (i.e., eyes), and procedures such as central lines, injections, and biopsies.1,2 Frequency and contour of the probe determine the picture that the clinician sees on the ultrasound (Fig. 1). FIGURE 1. View largeDownload slide Two probes: A 5 to 7 MHz curvilinear array probe on the left and a 10 to 12 MHz straight linear array or “small parts probe” on the right (note the labeled parts). FIGURE 1. View largeDownload slide Two probes: A 5 to 7 MHz curvilinear array probe on the left and a 10 to 12 MHz straight linear array or “small parts probe” on the right (note the labeled parts). Because of the different nature of examinations, uses for the probes, and types of probes, users of ultrasound in the austere environment at a minimum need two probes: the 10 to 12 MHz straight linear array probe for high resolution and either a low penetration curvilinear array or phased array microconvex and 5 to 7 MHz intracavity probe for deeper penetration. Linear array probes use a series of “crystals” to take pictures in a straight (or curved) line by using all of the crystals at relatively the same time.1 Compared to the phased array probe which oscillates which crystals are used in a pattern chosen by the machine for certain resolution and depth, this allows the probe head to be smaller and get into tighter places (between ribs, etc.).1 During times of necessity, certain probes may be used for other than their standard uses—in a series of combat care events, the U.S. Army used a small curved 5 to 7 MHz intracavity probe as a small parts probe for skin/soft tissues with good effect by changing the gain levels on the ultrasound machine.3 Although one probe can perform “double duty,” the resolution will be inferior to a dedicated probe. When a third probe can be afforded, a transvaginal probe may be useful for care of women in the expeditionary setting. Ultrasound technology was formerly only available to radiologists but has now become more accessible to adequately trained providers.1 Financial incentives, greater patient satisfaction, and improved diagnostic and treatment capability have driven the change to primary care and emergency medicine specialties routinely using ultrasound in “point of care” settings. Bedside ultrasound can be useful since it has no ionizing radiation; compared to other imaging modalities, it is often very cost-effective in the clinical setting. UTILITY OF ULTRASOUND IN THE AUSTERE ENVIRONMENT Even with the propagation of ultrasound in the clinic and emergency room setting, some question whether ultrasound matters and how it applies to clinical care in the austere setting. Some authors state that a good clinical examination can render an expensive ultrasound unnecessary.4 However, as cited in multiple studies below, evidence supporting ultrasound as a viable diagnostic and decision support tool in the austere setting is convincing. Complex triage decisions are required when determining whether a patient can be treated onsite or should be evacuated. Clinicians strive to avoid two extremes when making evacuation decision—both a high-risk, expensive evacuation for a problem that turns out to be low risk and a slower, but possibly safer, evacuation for a high-risk, immediate problem are to be avoided. Simultaneously, clinicians must consider what supplies and manpower are available for consumption if continued care is chosen over evacuation. Previous examples are cases where clinicians have successfully ruled out testicular torsion with a Doppler ultrasound saving a dangerous aeromedical evacuation and have ruled in cholelithiasis which required immediate evacuation for surgery.5 Ultrasound can help make informed decisions and has assisted in the triage of real patients. Although some argue that triage decisions should be made on clinical grounds, classic textbook presenting symptoms are often not actual presenting symptoms.4 A comparative case study regarding Focused Assessment with Sonography for Trauma (FAST) examinations of two patients illustrates this principle.6 Both patients suffered multiple penetrating trauma to the thorax and were taken to the same Level I trauma center for evaluation. “Patient 1” had unstable vitals and what appeared to be life-threatening injuries whereas “Patient 2” had stable vitals and what appeared to be nonlife threatening injuries. However, a FAST examination of “Patient 2” found a collection of blood in Morrison's pouch, the splenorenal recess, and the pelvis, whereas “Patient 1” had no intra-abdominal fluid. This information changed the initial clinical assessment that “Patient 1” needed emergent surgery, and instead, “Patient 2” was deemed the more injured. Small field hospitals, on-ship clinics, and remote area clinics now use FAST examinations routinely to improve triage ability—often avoiding evacuation to higher level care and saving precious resources in “resource strapped” environments.3,5 Ultrasound has been used in mass casualty triage outside the hospital in both the 1988 Armenia earthquake and the 2008 Wenchuan earthquake.7,8 Ultrasound can perform an accurate trauma evaluation in under 4 minutes—important when there are thousands of casualties.9 In a remote location in the Amazon, lengthy, and possibly dangerous, transfer was avoided in 28% of the cases where ultrasound was used.10 The team was able to effectively rule out gallstones and ectopic pregnancy as the cause of abdominal pain which “yielded a considerable savings in resources.”10 This study found that bedside ultrasound improved the diagnostic certainty in 72% of cases by narrowing the differential diagnosis. This group found the technology so useful that it has now been used in >20 temporary expeditionary clinics manned by volunteer physicians. Not only did the differential narrow, but in 17 of 25 patients, the certainty of the diagnoses improved. The physicians using this technology felt that it helped them save scarce resources and time.10 A French study evaluated 302 scans on 169 patients from prehospital ambulance response and found that in 67% of cases, it increased diagnostic certainty.11 The average examination time was 6 minutes, and the study found varied pathology such as pericardial effusions, pleural effusions, and vascular lesions, which were then confirmed by standard of care imaging once the patient arrived at the hospital.11 Based on these studies and others, the Emergency Medicine community is continuing research investigating the feasibility of moving ultrasound into the field to guide treatment by first responders or even nonclinical personnel.12,13 INDICATIONS Trauma The FAST examination is common in the hospital setting.14,15 This is a quick, 2 to 4 minute assessment performed on trauma victims in the Emergency Room. The examination assesses 4 areas—pericardium, right upper quadrant, left upper quadrant, and the pelvis around the bladder.14,15 The goal of this examination is to observe for free fluid after blunt trauma, which may indicate hemorrhage. This study has been found to be sensitive (83.3%) and very specific (99.7%).15 It is conceivable that the FAST examination could be used for risk stratification and evacuation decisions in austere environments since it has good sensitivity. In a hospital setting, a normotensive patient should be rechecked again in 6 hours after a negative FAST scan.14,15 However since the sensitivity is not 100%, a physician in the austere environment may not wait 6 hours on a medical evacuation because the FAST was negative. Conversely, with its outstanding specificity, a positive FAST should spur clinicians to argue for a higher risk, more rapid transport even in patients with stable vital signs. Additionally, this examination can easily be performed almost anywhere—even during aeromedical rapid transport with approximately the same sensitivity and specificity as in the hospital.16 Of course, cost, weight of the machine, predeployment training, and the evacuation environment should be considered before bringing the ultrasound on a mission. Pericardial Effusion In a review of studies in three prehospital settings, ultrasound cardiac examinations were “adequate” in approximately 94% of cases and diagnosed pericardial effusion with 100% sensitivity and specificity.13 In Emergency Department imaging, cardiac ultrasound has increased survival nearly two-fold in penetrating cardiac injury with the actual survival of the nonecho group versus the echo group being 57% and 100%, respectively (number needed to treat for prevention of a single mortality was 2.2).17 Of course, in cases of protracted evacuation, it is unlikely that this will greatly affect survival rates, but may encourage a clinician to evacuate a stable pericardial effusion rapidly once they have confirmed the diagnosis (Fig. 2). In cases of cardiac tamponade, an ultrasound guided procedure with a long needle could theoretically be better than the same lifesaving procedure done blind.4 In the austere environment, pericardiocentesis can be performed since the 30 mL syringe is ubiquitous and the 18-gauge spinal needle is normally carried in packs for relief of tension pneumothorax (PTX), and the success rate improves with ultrasound.4 FIGURE 2. View largeDownload slide Pericardial effusion without tamponade noted on bedside ultrasound. FIGURE 2. View largeDownload slide Pericardial effusion without tamponade noted on bedside ultrasound. Pneumothorax Ultrasound can be used to exclude or diagnose PTX. A 2001 case report of an 18-year-old skier who fell forward onto his chest detailed how, on the mountain, ultrasound was used to rule out a PTX.18 PTX is diagnosed by the absence of normal lung sliding along the pleura under ultrasound.18 As little as 150 mL of air in normal gravity and only 50 mL in microgravity can be seen on the anterior portion of the chest.19 Recent meta-analysis of 20 studies shows that ultrasound is more sensitive and as specific than anteroposterior chest radiography (88% and 99%, respectively, for ultrasound versus 52% and 100%, respectively, for chest radiography).20 Although clinicians without ultrasound may choose to place a thoracostomy tube before air evacuation, there is both risk with this procedure and loss of critical supplies.19 PTX can decompensate during air evacuation in unpressurized aircraft—patients could be evaluated preflight for a PTX given the clinical scenario and “ruled out.” Pre- and mid-flight evaluation can also be used to assess the patient and either place the thoracostomy tube or delay placing a chest tube if the patient's examination is stable.21 Since PTX and hemothorax are known causes of preventable death, ultrasound can be a useful modality to evaluate those who do not clinically “declare themselves.” Musculoskeletal Normally, musculoskeletal imaging involves large X-ray machines or magnetic resonance imaging, but there is an increasing evidence base to support the use of ultrasound in the outpatient clinical setting.5,22,25 Portable ultrasonography is currently used by the U.S. military to evaluate musculoskeletal trauma in forward-deployed locations.3,5 Ultrasound is known to be very effective when evaluating for long bone fractures—sensitivity for midshaft fractures approach 100% in one study.22 In a study of 20 nonultrasound-trained EMT's, they were given 2 minutes of ultrasound training and were then able to evaluate long bone fractures in a controlled environment with a final sensitivity of 97.5% (95% CI: 94.1–100, p < 0.05) and specificity of 95% (95% CI: 85.4–100, p < 0.05).23 As with most targeted single area ultrasounds, the evaluations were able to be completed in <5 minutes.9,23 Additionally, ultrasound has been successfully used to guide reduction of fractures without using standard radiographs.24 Quick evaluation with ultrasound could eliminate the need for an evacuation by ruling out a fracture immediately. Of course, there are limitations to ultrasound for fracture evaluation as this modality is best for superficial long bone fractures and can have problems seeing deeper, nondisplaced, or incomplete fractures. However, assessment of complicated fractures can allow for an appropriate evacuation destination to be chosen to eliminate sending the wrong injury to the wrong hospital. Beyond fracture recognition and diagnosis, ultrasound has promise for use in remote locations to evaluate for abscesses and foreign objects. Although it could be argued that abscesses can be diagnosed on clinical grounds, most clinicians have had experience with an incision and drainage of an abscess that was surprisingly large and needed extensive packing. Training models can help providers recognize an abscess with ultrasound that can be safely drained with minimal/no packing and allow appropriate disposition in an austere environment.26 Foreign bodies can also be identified successfully by ultrasound in forward operating bases.3,5 Although in an early phase of development, animal model data using sea urchin spines indicates ultrasound may be useful in ruling out intra-articular foreign body—sensitivity of 100% (95% CI: 46.3–100) and specificity of 75% (95% CI: 21.9–98.7).27 High-Altitude Pulmonary Edema High-altitude pulmonary edema (HAPE) is pulmonary edema that develops in climbers at high altitudes.28 Since its symptoms are often vague and nonspecific, some have used ultrasound to assist with the diagnosis of HAPE.9,29 Ultrasound can be used to attempt to find the “comet tail” pattern found where there is increased microreflections of sound waves by increased pulmonary edema (Fig. 3).29,30,31 These comet tails have been shown to correlate well with both clinical symptoms and oxygen saturations in climbers—for each change in the comet tail pattern by 1 point, based on the scoring system used in the study, the oxygen saturations decreased by 0.67% (95% CI: 0.41 to 0.93, p < 0.001).31 Of course, since they seem to correlate so well with ultrasound findings, clinicians can use oxygen saturations directly and ultrasound may not be necessary.30 HAPE can be distinguished from left ventricular failure in either trained hands or via telemedicine by assessing the pulmonary wedge pressure. Those with HAPE can be allowed to descend, and then once symptoms resolve, slowly ascend versus those with decompensated left ventricular failure who should be immediately evacuated.29,31 FIGURE 3. View largeDownload slide Echogenic lines showing “comet tail” pattern, otherwise known as “lung rockets” in a patient with pulmonary edema. This is an artifact caused by increased microreflections of sound waves by increased pulmonary edema. FIGURE 3. View largeDownload slide Echogenic lines showing “comet tail” pattern, otherwise known as “lung rockets” in a patient with pulmonary edema. This is an artifact caused by increased microreflections of sound waves by increased pulmonary edema. Based on data from one intensive care unit study involving ultrasound in pulmonary diseases following the Bedside Lung Ultrasound in Emergency (BLUE) protocol, an algorithm evaluating lung sliding and the specific category of the ultrasound picture, ultrasound yielded the proper diagnosis in 90.5% of the cases.32 This allows the providers to differentiate between pulmonary edema (97% specificity, 89% sensitivity) versus PTX (100% specificity, 88% sensitivity) versus pneumonia (94% specificity, 89% sensitivity).32 Limitations of this study include the high level of experience of these providers and the elimination of 15% of the initial patients enrolled from the final statistics based on either rare, unknown, or multiple diagnosis. Therefore, this data will be less useful in the austere setting, although further research may yield translatable results. Acute Mountain Sickness Acute mountain sickness (AMS) is a syndrome that includes a headache in conjunction with fatigue, dizziness, lassitude, poor sleep, or gastrointestinal symptoms.33 AMS is thought to be caused by increased intracranial pressure (ICP) with associated edema or vasodilation.33 Increases in optic nerve sheath diameter (ONSD) are associated with increased ICP, but experts debate the exact cutoff (5.0 to 5.8 mm).34,35,36 In two field studies at altitude, increasing ONSD was associated with increasing AMS scores at altitude (p < 0.001 for both studies).37,38 Although these were proof of concept studies, the data could be useful in the field to help differentiate AMS from other conditions such as intoxications, viral illnesses, or poisonings which may mimic AMS but are not associated with increased ICP. Also, high altitude cerebral edema (HACE) which is the deadly end point of AMS, could, in theory, be ruled out with normal ONSD and thus change evacuation priorities (Fig. 4). FIGURE 4. View largeDownload slide The posterior lens of the eye is seen along with the retina, and inferiorly the optic nerve. FIGURE 4. View largeDownload slide The posterior lens of the eye is seen along with the retina, and inferiorly the optic nerve. Eye Injury and Pathology Ultrasound does an impressive job imaging the globe, and this examination is simple enough to even be done by nonclinicians in a telemedicine scenario as seen in a series of space shuttle experiments which found that an individual with limited ultrasonography skill can still visualize all anatomical aspects of the eye.39 Additionally, the military has used eye ultrasound in austere settings to diagnose both foreign bodies and retinal detachments.3 Although ultrasound can be very accurate in diagnosing eye injury, clinical diagnosis will likely be more useful than imaging in almost all cases. Rapid diagnosis, pain control, an eyeshield, and evacuation as needed are the key to preventing loss of eyesight. Ultrasound would be somewhat useful to confirm a globe penetration or retinal detachment and then evacuate to a specific hospital with an ophthalmologist. Stroke Cerebral vascular accidents (CVA) or stroke can be diagnosed with the right ultrasound equipment. In a German case series of 25 patients in a prehospital setting (patient homes or medical transport), a trained physician (in Germany physicians ride with the emergency response service) visualized and measured flow in the middle cerebral artery in 20/25 patients showing that using trained physicians to diagnose CVA is “feasible” in nonhospital settings.40 Another case report identified a 49-year-old climber who was diagnosed, and theoretically, treated, with ultrasound.41 Transcranial Doppler was available in that case, and a middle cerebral infarct was diagnosed. Clinicians started aspirin and left the ultrasound in place for 12 hours, in which initial limited data shows may actually be therapeutic for stroke victims.42 The ultrasound machine and probe must be capable of transcranial Doppler, which can be confirmed after discussion with the ultrasound supply company. CVA is a rare condition on expeditions, so the use of an ultrasound for its diagnosis may be more appropriate as a “bonus” rather than the primary reason to have this machine in austere settings. Obstetrics Although obstetrical ultrasound examination is common in Obstetrical and Family Medicine clinics in the United States, the utility of it in the deployed setting is questionable as a result of low rates of pregnancy. Local nationals are usually either full term when the diagnostic ability of ultrasound is of little use or, in early first trimester, when they are being worked up for abdominal pain with a positive pregnancy test.43 In the latter situation, lack of the appropriate probe will likely limit the utility of ultrasound since a transabdominal probe is not sensitive enough to rule out ectopic pregnancy. Although a clinician may want to rule out this life-threatening condition, unless a transvaginal probe is available, the patient should be immediately evacuated if ectopic pregnancy is suspected. As a transvaginal probe has very few uses, unlike other probes, it is less likely to be found in austere settings given the extra weight and cost. However, for those in austere clinic settings seeing indigenous populations, acquisition of a transvaginal probe may be justified. SPECIFIC TYPES AND QUALITIES OF ULTRASOUND MACHINES There are many types of ultrasound machines, and the exact type needed depends on the mission, supplies, and expected injuries. Table I details various ultrasound machines that are considered portable, but still versatile. Another stumbling block, beyond cost, is how to charge the unit on a remote mission. Although some small field locations have grid or generator power, some locations will need to use solar charging.45 Additionally, rapid response search and rescue or emergency personnel with a home base can also detach their units and use them on battery reserve for various times. TABLE I. Comparison of Various Ultrasound Machines on the Market Today2,44 Manufacture  Model  Price (in USD $)  Weight  Probe Options  Battery Life  Hardness  Cited Articles  GE  V-Scan  $7,900  390 g  Curved 1.7–3.8 MHz (75° With Maximum Depth of 25 cm)  2 hours  Operating Temperature Not Available. Drop Tested to 3 ft    SonoSite  180 (Retired)  $5,000a  2.59 kg  Multiple (2–13 MHz Both Convex and Linear)  2–4 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20 to 60°C (−4°F to140°F); Drop Tested to 3 ft  3, 4, and 7  SonoSite  M-Turbo  $23,000b  3.9 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    SonoSite  MicroMaxx  $30,000b  3.5 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    GE  LOGIQ e  $28,000b  4.5 kg  Multiple (2–13 MHz Both Convex and Linear)  4 hours LiON  10°C–40°C Operating; Storage −5°C to 50°C  6  GE  LogiqBook XP  $25,000b  4.2 kg  Multiple (2–13 MHz Both Convex and Linear)  1 hour LiON  10–40°C Operating; Storage −5°C to 50°C    Siemens  Acuson P10  $8,500b  0.7 kg  Curved 2–4 MHz (Maximum Depth of 24 cm)  1 hour LiON (With Quick Change Spare)  Not Available    Manufacture  Model  Price (in USD $)  Weight  Probe Options  Battery Life  Hardness  Cited Articles  GE  V-Scan  $7,900  390 g  Curved 1.7–3.8 MHz (75° With Maximum Depth of 25 cm)  2 hours  Operating Temperature Not Available. Drop Tested to 3 ft    SonoSite  180 (Retired)  $5,000a  2.59 kg  Multiple (2–13 MHz Both Convex and Linear)  2–4 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20 to 60°C (−4°F to140°F); Drop Tested to 3 ft  3, 4, and 7  SonoSite  M-Turbo  $23,000b  3.9 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    SonoSite  MicroMaxx  $30,000b  3.5 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    GE  LOGIQ e  $28,000b  4.5 kg  Multiple (2–13 MHz Both Convex and Linear)  4 hours LiON  10°C–40°C Operating; Storage −5°C to 50°C  6  GE  LogiqBook XP  $25,000b  4.2 kg  Multiple (2–13 MHz Both Convex and Linear)  1 hour LiON  10–40°C Operating; Storage −5°C to 50°C    Siemens  Acuson P10  $8,500b  0.7 kg  Curved 2–4 MHz (Maximum Depth of 24 cm)  1 hour LiON (With Quick Change Spare)  Not Available    All information above is either from a company directly or from publicly available information when the company did not respond to information request. a Available online through various dealers. b Online price with probes—company did not respond to request for direct purchase price in time for publishment. View Large TABLE I. Comparison of Various Ultrasound Machines on the Market Today2,44 Manufacture  Model  Price (in USD $)  Weight  Probe Options  Battery Life  Hardness  Cited Articles  GE  V-Scan  $7,900  390 g  Curved 1.7–3.8 MHz (75° With Maximum Depth of 25 cm)  2 hours  Operating Temperature Not Available. Drop Tested to 3 ft    SonoSite  180 (Retired)  $5,000a  2.59 kg  Multiple (2–13 MHz Both Convex and Linear)  2–4 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20 to 60°C (−4°F to140°F); Drop Tested to 3 ft  3, 4, and 7  SonoSite  M-Turbo  $23,000b  3.9 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    SonoSite  MicroMaxx  $30,000b  3.5 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    GE  LOGIQ e  $28,000b  4.5 kg  Multiple (2–13 MHz Both Convex and Linear)  4 hours LiON  10°C–40°C Operating; Storage −5°C to 50°C  6  GE  LogiqBook XP  $25,000b  4.2 kg  Multiple (2–13 MHz Both Convex and Linear)  1 hour LiON  10–40°C Operating; Storage −5°C to 50°C    Siemens  Acuson P10  $8,500b  0.7 kg  Curved 2–4 MHz (Maximum Depth of 24 cm)  1 hour LiON (With Quick Change Spare)  Not Available    Manufacture  Model  Price (in USD $)  Weight  Probe Options  Battery Life  Hardness  Cited Articles  GE  V-Scan  $7,900  390 g  Curved 1.7–3.8 MHz (75° With Maximum Depth of 25 cm)  2 hours  Operating Temperature Not Available. Drop Tested to 3 ft    SonoSite  180 (Retired)  $5,000a  2.59 kg  Multiple (2–13 MHz Both Convex and Linear)  2–4 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20 to 60°C (−4°F to140°F); Drop Tested to 3 ft  3, 4, and 7  SonoSite  M-Turbo  $23,000b  3.9 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    SonoSite  MicroMaxx  $30,000b  3.5 kg  Multiple (2–13 MHz Both Convex and Linear)  2 hours LiON  10°C–40°C (50°F–104°F), 15%–95% R.H. Operating; Storage −20°C to 60°C (−4°F to 140°F); Drop Tested to 3 ft    GE  LOGIQ e  $28,000b  4.5 kg  Multiple (2–13 MHz Both Convex and Linear)  4 hours LiON  10°C–40°C Operating; Storage −5°C to 50°C  6  GE  LogiqBook XP  $25,000b  4.2 kg  Multiple (2–13 MHz Both Convex and Linear)  1 hour LiON  10–40°C Operating; Storage −5°C to 50°C    Siemens  Acuson P10  $8,500b  0.7 kg  Curved 2–4 MHz (Maximum Depth of 24 cm)  1 hour LiON (With Quick Change Spare)  Not Available    All information above is either from a company directly or from publicly available information when the company did not respond to information request. a Available online through various dealers. b Online price with probes—company did not respond to request for direct purchase price in time for publishment. View Large These machines are often very rugged and can survive in multiple environments. They have been used by NASA in low-earth orbit—which involved both high- and low-gravity environments.12,37,46 The U.S. military uses these machines in dusty, hot, cold, humid, and arid environments all around the world with little difficulty.3,5 Some of these areas are very austere and include tent conditions with unreliable power, but these machines are still trusted as reliable and useful in these caustic environments. Their use has spread to both indoor and outdoor dirty conditions during disaster relief and medical missions.7,8,10,47 Ultrasound has also been used in unpressurized aeromedical evacuation in many situations and studies.13,16,21,40 Generally, the probe is considered the most fragile part given the crystal array, and care should be taken to ensure proper storage in a shockproof case for transportation. The choice to purchase an ultrasound will be directly related to its utility for each mission. Factors such as training, budget, patient population, resources, clinic location, and evacuation abilities must be taken into account when deciding on which, if any, ultrasound machine should be purchased for an either a mission or static clinic. As technology improves, machines get smaller and more portable while the price tends to decrease. Refurbished machines are available for significant savings. TRAINING Naturally, any technology is useless without someone to interpret the data. Some have wondered if wilderness medicine providers have adequate training to use ultrasound effectively in austere settings.4 Increasing numbers of clinicians are trained to use ultrasound for point-of-care assessment in the clinic and Emergency Department.1 It is often part of residency training in Primary Care, General Surgery, and Emergency Medicine. Some would even say that ultrasound has replaced physical examination skills in a younger generation of physicians.13 As with most procedures, there are training recommendations for the appropriate number of ultrasound that a clinician requires to be considered adequately trained—the American College of Radiology and American Institute of Ultrasound in Medicine recommend 300 to 500 cases and 3 months of training.48 However, some data suggests that 200 cases is the “lowest limit” but not even sufficient for some radiologists.48 As with many procedures in medicine, there is disagreement about competency requirements between specialty societies. Nonradiology societies such as the Society for Academic Emergency Medicine and the American Academy of Family Physicians argue for much lower numbers based on competency performing the specific point-of-care ultrasound procedures instead of minimum numbers since targeted examinations can be focused. Streaming/Remote Viewing If specialized training is not an option for a clinician, or if the patient is a difficult case, then video streaming can be utilized to allow remote evaluation by a radiologist. This technology has been used multiple times during evaluations by NASA, where nonmedical personnel use ultrasound with specific instructions and this information is beamed real time down to a provider on the ground.12,39,46 Nonmedical personnel did require appropriate training to get the correct views, but this training takes 2 to 3 hours and can be reinforced with a simple guide showing the proper technique.12,25,39,46 Streaming has also been used in austere settings such as Mt. Everest (2009) where, in a proof of concept study, the ultrasound was connected to a data conversion device then a laptop computer for streaming.31 Voice Over Internet Protocol was then used by the radiologist to communicate with the nonradiologist at the point of care. Most commercial ultrasounds have USB connection options, and data streaming can be used through most computers with the appropriate software. Of course, there is extra cost, weight and power consumption for the computer to process the images, and an Internet connection is needed to send the images. Additionally, weather may interfere with satellite systems, but more areas are using cell phone technology or hardwired connections that are not as susceptible to weather. “THE FUTURE” As ultrasound begins to play a role in the austere environment, the technology continues to improve with faster processing power and more features.1,4,49 The future of ultrasound will most likely utilize software in a smart phone.50 A device such as this would allow a micro-USB probe to attach to the smart phone and allow the user to carry their own ultrasound machine everywhere they go (yes, we are entering the world of the Star Trek tricorder). Current USB probes cost approximately $2,000, but these probes will likely be $500 within the near future.50 CONCLUSION In approximately 10 years, ultrasound has gone from a modality normally scheduled in the Radiology Department to one now routinely performed in the office. Ultrasound is now feasible and increasingly common in the austere setting since it improves diagnostic certainty and ability to triage injuries in a poor logistics situation. It has been used in multiple environments and may assist a lone physician with little supplies who has to decide between slow and safe transportation versus a rapid, but more dangerous, approach. Ultrasound has become faster, cheaper, more portable, more rugged, and more versatile. There appears to be a future in austere and deployed medicine for ultrasound. REFERENCES 1. Moore CL, Copel JA Current concepts: point-of-care-ultrasonography. N Engl J Med  2011; 364( 8): 749– 57. Google Scholar CrossRef Search ADS PubMed  2. 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TI - Ultrasound in the Austere Environment: A Review of the History, Indications, and Specifications
JO - Military Medicine
DO - 10.7205/MILMED-D-12-00267
DA - 2013-01-01
UR - https://www.deepdyve.com/lp/oxford-university-press/ultrasound-in-the-austere-environment-a-review-of-the-history-0cXmtgIXxe
SP - 21
EP - 28
VL - 178
IS - 1
DP - DeepDyve
ER -