Manual of Austere and Prehospital Ultrasound

Ultrasound has rapidly become integral to the practice of emergency medicine. Over the past few years, with improvements in device size and cost, there has been increasing interest in exploring the utility of ultrasound in the prehospital environment. Much of the available literature on ultrasound in the emergency setting focuses on care delivered in emergency departments and intensive care units within the developed world. As a result, most resources are inappropriate and inadequate for doctors and non-physicians practicing in out-of-hospital environments that, by definition, are resource limited. This manual fills that gap by focusing on simplified discussions of ultrasound studies, ultrasound physics, and research that impacts out-of-hospital care in order to meet the needs of prehospital and austere providers.
The manual discusses the use of ultrasound for diagnosis in out-of-hospital care, advanced noninvasive monitoring of patients, and safety in performing procedures common to the prehospital and austere environment. As is the approach for prehospital education, the chapters are complaint based and not diagnosis based where applicable. Chapters cover ultrasound image interpretation and basic physics; common image adjustments to improve image quality; unique challenges found in urban prehospital environments, austere/wilderness environments, tactical environments, and military special operations environments; and initial training, quality improvement/assurance programs, and credentialing. It also includes a section on procedures such as pericardiocentesis, vascular access, cricothyroidotomy, and others specific to austere providers. The Manual of Austere and Prehospital Ultrasound is an essential resource for physicians and related professionals, residents, and medical students in emergency medicine, civilian and military EMS providers, and critical care flight paramedics and nurses.

• Language: English
• Publisher: Springer
• Release date: Jan 27, 2021
• ISBN: 9783030642877

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Part IIntroduction and Background

© Springer Nature Switzerland AG 2021

B. D. Nicholson et al. (eds.)Manual of Austere and Prehospital Ultrasoundhttps://doi.org/10.1007/978-3-030-64287-7_1

Physics and Knobs

Michael Joyce¹   and Robert Stenberg²

(1)

Department of Emergency Medicine, Virginia Commonwealth University, Richmond, VA, USA

(2)

Emergency Department, Cleveland Clinic Akron General, Akron, OH, USA

Michael Joyce

Email: [e-mail]

Keywords

PhysicsArtifactReverberationDopplerFrequencyDepthGainFocal zoneEnhancementImage acquisition

Introduction

Understanding the physics behind how an ultrasound machine obtains images may seem like an unnecessary endeavor, but having a solid understanding of what is behind the image can help make interpretations easy and quick. In fact, most of what we use to diagnose pathology is based on an object changing the way the sound behaves, and thus distorting our image.

Ultrasound is mechanical waves at frequencies beyond what the human ear can detect. Our ears top out at around 20,000 hertz (Hz). Diagnostic imaging starts around 1 million Hz, or 1 megahertz (MHz) and usually goes up to around 15–20 MHz deepening on application. All of the probes in use for point of care ultrasound are variable frequency probes; meaning you can adjust the frequency of them to improve your image. Having a solid foundation in the relationship between frequency, resolution and depth will help you obtain top quality images.

Principles

Sound applications are all over our world, including such things as police radar guns, sonar on large navy ships and echolocation in animals. All of these applications, including diagnostic medical ultrasound rely on the principal that sound velocity through a medium is a constant, and thus you can calculate how long it should take for sound to travel to an object and back. Simple applications, such as sonar on a boat, do not require any further modification by a computer. Just time the sound, listen for it to come back, and you get a distance. The sound is always travelling through the same medium (water) and thus always behaves the same. Unfortunately, for diagnostic ultrasound, the sound must travel through multiple different mediums making for lots of changes in how the sound propagates, but fortunately, we can use these differences to help us interpret what we are seeing inside the body.

In point of care ultrasound, the sound image is usually created by a piezoelectric crystal that can both create the sound by converting electricity into a mechanical sound wave and re-absorb the sound and change it back to an electrical signal, therefore acting as an all in one device. Newer machines are starting to use silicone chips to accomplish the same feat, which has brought down the price and size of machines.

Ultrasound does this sound production/collection in two main fashions: continuous wave, and pulse wave echo.

Continuous wave is what is used in doppler machines to check for fetal heart tones and pulses, but also with more complex flow measurements such as vascular studies on diagnostic ultrasound. For continues wave, there is constantly sound being sent out and also being read. This allows for us to determine changes in frequency only (the Doppler effect), but not distance (if you are always sending sound, there is no way to decipher when a wave has returned that you sent out). The familiar example of Doppler effect is the ambulance approaching us and then going away. As the ambulance approaches, the frequency increases and the sound frequency (pitch) becomes higher and higher. After it passes, the frequency slowly decreases and the sound pitch gets lower and lower. Diagnostic ultrasound uses this principle to determine both the direction and the speed of the moving object – in our case the blood. If the frequency is increasing, the blood is coming towards you and if the frequency is decreasing, it is moving away from you. The machine can also determine how rapidly the frequency is changing and determine the speed as well!

This type of ultrasound was all we had at first, and is very similar to the simplistic sonar machines in boats. With the advent of rapidly improving computers however, pulse wave echo was invented. Instead of always sending and always listening, now the machine will send out a pulse of sound waves, and then wait for them to come back. Now – it can calculate just how far away that image is by timing how long it takes to return. Then, it does this again, and again, and again, until it has a map of all the things in its line of sight. If you speed this process up sending thousands of pulses per second, you can get a live image of all the objects in front of you. Now we have diagnostic ultrasound!

The next step then is to get that sound into the body at different depths. As we have discussed, the sound must travel through different tissues to get to our target organ or object. The further the sound has to go, the harder it is for the sound to get there. If it has to travel through skin, adipose, muscle, a kidney, more adipose and then to the aorta, a lot of the sound is going to bounce off and not make it, or will run out of energy. This happens by a multitude of different reasons, such as absorption, refraction, reflection and scatter. A higher frequency sound succumbs to these problems much easier than a lower frequency sound. A good example is to think of treble and bass notes in music. A singer who is singing a very high pitch (high frequency) note will be heard very clearly by people right in front of them, but those off at a distance may not even hear it as it disperses. A bass note from a large subwoofer however, can be heard blocks away – but does not carry the same clarity. The same thing happens in diagnostic ultrasound. If we use really high frequency sounds, it does not go far, but gives us very good resolution. If however, we need to get way down deep, we can use a low frequency sound to travel further, but in trade give up some of our resolution.

Thus, on the machine, the depth button is really just the frequency button! If you turn the dial to increase your depth, you are decreasing the frequency, and vice versa. To obtain an ideal image, you should use only the lowest frequency needed. So if your target image is at the very top of your screen, decrease the depth until you only see the object of interest on the screen, and your resolution will dramatically improve!

The final principal that is essential to understand so you can obtain great images is gain. Gain is not contrast! When you increase the contrast on your TV for example, you are increasing the ability to differentiate two different pixels by changing each pixels level of brightness. In ultrasound, we cannot just change our pixels like a TV can because we are relying on the sound that returns to make our image. If not much sound returns (due to absorption, refraction, scatter, etc) then our image will look very dark. What we can do then, is turn up the gain, which increases the perceived intensity of the signal that is interpreted. So if the signal at first registered to the machine as 5/10 intensity, turning the gain up can make it look like a 7/10 intensity. This is great, but it also increases the signal from all the objects coming back because it cannot decipher which pixel we want to see better like a TV. Thus, there is a sweet spot with gain, and if you add too much, all you will see is 10/10 intensity everywhere, or a white screen! If your gain is too low though, you will see all 1/10 intensities and a black or very dark screen. Thus, you should find a gain that allows you to see the most objects without making them all white.

Image Optimization

Now that we understand how the image is created, before you interpret the image you must optimize it. This is an often-overlooked step by new sonographers. When you place the probe on the patient and see the image you were hoping for, you can get excited and start trying to make the diagnosis immediately. However, you are placing yourself at a great handicap. Optimizing all of the following things will make for images that can be interpreted with much higher accuracy!

Probe Selection

Selecting a probe to match your application is essential. There are innumerable probes on the market, but all have certain things in common that you need to decide on. The first is the frequency. As we discussed, a higher frequency will only travel a short distance, but provide a very high quality image. These probes are good for imaging near the surface, such as skin, muscle, nerves, extremity vessels and eyes. Lower frequency probes are used for deeper imaging, such as in the abdominal cavity and the thoracic cavity. The second major characteristic is the footprint. This is just how big the sound transmitting area is. A smaller footprint, can get into smaller places, but only give a very narrow image width. A larger probe can give a large viewing area, but can be difficult to get all the crystals touching the skin and thus the sound into the body.

Ideally, you would have one probe that can do low frequency and one probe that can do high frequency, but this is not always an option. In austere environments, if you had to pick one probe to bring with you, a lower frequency probe is likely best as it can still see superficial structures, just with less resolution. As mentioned however, new silicone chips are coming on the market, and these chips are able to span a much wider frequency range (such as 1–15 MHz!).

In short, select the probe that can provide the highest frequency image for your application if you have multiple to choose from. If imaging between structures, such as the ribs to see the heart, you will also need a smaller footprint.

Depth

Once you have selected your probe and found your image, you need to adjust the depth. As we already discussed, changing the depth is just changing the frequency. To optimize your depth, place the target object so it takes up most of the screen. Any depth beyond the structure you are looking at means your frequency is lower than it needs to be, and thus sacrificing resolution. An example is looking at the heart. If you have the heart taking up the top half of the screen, but the bottom half of the screen is all structures deep to the heart, your depth is too deep and your image could be better. Alternatively, if you are cutting off the bottom part of your heart and can only see half, you do not have enough depth to see all the potential pathology and may miss something important!

Gain

Now that you have the image at the right depth, you should change the gain so that you can see as many structures as possible without making the whole screen white. Frequently, you will find yourself increasing the gain until you see what you were looking for. Again, using the heart as an example, if you cannot tell the difference between the walls and the chambers, your gain is too low. If however, the inside of the chambers look white just like the walls, then your gain is too high!

Focal Zone

The focal zone is the area of the screen where the computer dedicates the most processing power and listening skills to make the image clearer. Most point of care machines do not give you the ability to adjust the focal zone (in an attempt to keep costs low), and the focal zone is therefore right in the center of your screen. If you do not have a focal zone adjustment, place the object of interest exactly in the center of the screen and you will be using the best computing power available for image creation.

Artifacts

Now that we have an optimized image, we must consider artifacts that are being created. Even though we have toted how amazingly smart ultrasound imaging is, in reality it is still very basic and makes a lot of mistakes. The majority of artifacts are produced secondary to assumptions the machine is making while receiving the sound. The machine assumes that any sound that comes back has travelled on a straight line into the tissue and then back. But we know, sound can bounce around and come back from different locations. Or – sound can hit a wall and none of the sound can get past. Or the sound can hit some fluid and not bounce back at all and instead travel right through it before bouncing back. The machine does not know this, but you do and can use these artifacts to interpret what is going on. If sound hits a poor transmitter (bone), all the sound bounces back and is displayed as very bright hyperechoic (hyper-lots echoic-sound). If all the sound transmits really well say through a fluid filled structure, then no sound bounces back and you get a dark hypoechoic (hypo-few echoic-sound) signal. Lets look at some of the artifacts this creates.

Shadowing

Shadowing , or acoustic shadowing is when there are no images seen beyond a structure. The common example is bone, such as ribs. The ultrasound waves are highly absorbed or reflected, and no ultrasound is propagated past them. Shadowing can be differentiated further into clean and dirty. Clean shadowing is traditionally seen where there is no signal seen past the region, such as bones or renal/biliary calculi. Dirty shadowing, is typically secondary to gas, and some sound still gets through but much less than would be expected.

Reverberation

When sound bounces between two highly reflective structures, the machine repeats the image downward. This is commonly seen with highly reflective foreign bodies such as metal or glass. In normal lung, A-lines can also be seen, which is reverberation of the parietal pleural line.

Mirror Artifact

Mirror artifact literally produces a mirror type image of something seen nearer to the probe. Clinically, this is often seen above the diaphragm, and is normal. If there is absence of mirror artifact superior to the diaphragm, and replaced by a hypoechoic area, there is suspicion or a pleural effusion. Similar to reverberation, where the ultrasound beam strikes a highly reflective surface. The beam then bounces back and forth between structures causing a delayed return to the transducer, and the transducer then thinking it is deeper than it actually is.

Edge Artifact

Also known as edge shadowing or lateral edge shadowing, occurs from refraction as a beam obliquely hits a tissue boundary. This is classically seen in circular structures as the gallbladder, where the lateral edges of the hyperechoic wall produce shadowing beneath it. If not recognized properly, this can be mistaken as a stone due to the shadowing posterior to it.

Posterior Enhancement

Enhancement is seen in large fluid-filled structures. It can often be seen in a full bladder. It happens as the fluid transduces the sound faster and attenuates less than the machine expects, and increases the signal that it thinks it sees.

Aliasing

This is an error seen in doppler imaging, and in many other scenarios outside of ultrasound. It is a problem of under sampling, when something is moving faster than what is trying to observe it. Real world examples include when wheels are spinning so fast, to the human eye, they look like they are going backwards. In ultrasound and film, the frame rate is too slow to interpret which way it is going.

Image Acquisition/Probe Movements

Finally, when obtaining your image, you must be able to manipulate the probe to find and improve your image or to visualize entire structures. Since your plane of sound is only in two dimensions, to view an entire three-dimensional image you must scan through the structure. You would never only look at a single slice of a CT image, and thus you must create all the different slices and put them together in your head with ultrasound. This is arguably the hardest skill in ultrasound, and can only be perfected by lots and lots of hands on practice.

There are a few principles to know here, and to have common language across sonographers. To start, the probe marker should be towards the patient’s right if scanning transversely, and towards the patient’s head when scanning in the sagittal or coronal plane. To search for a structure of interest, it is best to start by scanning, which is essentially moving the probe left, right, up or down without changing the angle or rotation of the probe. This will help you visualize an entire area in the body and find the structure you are looking for. Once you have found the image, you can then fan through the organ to create your slices. This is accomplished by anchoring the probe to the skin, and then changing the angle of the sound to the left, right, up or down. This will keep the organ of interest in the center of the screen, while creating different planes through it.

If performing a procedure with the ultrasound, it is best to keep the probe and probe marker on the screen to the left to prevent disorientation.

Before you start scanning, you should become familiar with the knobs on your machine. Since each machine is different, it would be impossible to explain them all in this text. However, with your knowledge of how the machine works now, you can find all the important ones very quickly. Locate the depth and gain buttons, determine the probe you are using, the mode you want to use (Doppler vs pulse echo), where the freeze image buttons and save video clip buttons are, and you will be ready to start scanning!

Part II

Introduction to Considerations for Specific Environments

The following section is aimed at introducing a variety of unique out-of-hospital environments and the challenges providers face working in these settings.

Ground Emergency Medical Services (EMS) includes systems across the spectrum of out-of-hospital care including prehospital systems as well as interfacility transfers.

Helicopter EMS focuses on the challenges flight crews face providing critical care transport of severely injured and critically ill patients.

Military special operations continue to work in the far forward environment. As major large scale combat operations shift to smaller operational footprints across a wider area, special operations medical providers find themselves caring for critical patients for longer periods of time and needing to care for illness and injuries not related to combat wounds. The concept of prolonged field care has been introduced to describe the challenges of this new type of operational environment.

Urban search and rescue teams respond to a range of natural and manmade disasters that impact both the local population as well as the health infrastructure.

The environment is paramount to determining the applicability of any new technology. As various out-of-hospital providers consider adding ultrasound to their practice, it is important that the benefits of ultrasound be fully consider alongside the challenges this technology may create. Ultrasound remains a powerful imaging technology that benefits patients in the hands of appropriately trained providers.

© Springer Nature Switzerland AG 2021

B. D. Nicholson et al. (eds.)Manual of Austere and Prehospital Ultrasoundhttps://doi.org/10.1007/978-3-030-64287-7_2

Ground Emergency Medical Services

Benjamin D. Nicholson¹  , Harinder S. Dhindsa¹ and Michael J. Vitto¹

(1)

Department of Emergency Medicine, Virginia Commonwealth University School of Medicine, Richmond, VA, USA

Benjamin D. Nicholson

Email: [e-mail]

Keywords

EMSPrehospitalOut-of-hospital careMedical directionCostVolunteerCareer

Introduction

Ground EMS in high income settings includes a wide range of types of programs, response characteristics, patient complaints, and transport times. Ultrasound may provide a benefit to certain patients in certain situations, but implementation likely comes at a cost that may not be reasonable for certain situations.

In this chapter we will introduce certain situations that are unique to the ground EMS environment and should be considered before implementing ultrasound in ground EMS systems. Topics to be considered include: cost of acquiring equipment; training related costs; challenges of both career and volunteer EMS agencies; providing oversight including quality assurance and quality improvement programs; protocol development.

Cost

Implementing ultrasound in the ground EMS environment involves costs that include both training and equipment. EMS departments will also need to include budgets for updating equipment as new technology becomes available, ensuring that there is appropriate storage of images and the associated costs. Training costs will include initial training and recurrence. Training will also need to be provide if additional scans are added to protocols such as a department moving from eFAST to echocardiogram to ultrasound guided IVs. As with implementing anything new, these costs come at the expense of decreased opportunity to train in other areas and update other equipment.

Volunteer and Career Considerations

In the United States, many EMS agencies still rely heavily on volunteers and the unique challenges of this work force must be considered before implementing ultrasound. Challenges include the ability of all providers to make initial training, buy in of volunteer providers to adding a new skill, ability to maintain competency in this skill if they are only working a limited number of hours per week, month, or year. Each of these challenges must be considered prior to implementing an ultrasound programs. While it is easier to mandate training of career providers, this comes at the cost of overtime, potentially increasing burn out, and taking away from their personal time. Mixed departments may find this particularly challenging as they have different standards for what they can require of each provider. If the new skill were technology is rolled out to career only, volunteer providers may feel slighted.

Medical Director Oversight

Medicaldirectors must provide sufficient oversight of the providers and his commute challenging in large department. This includes a sufficient quality assurance in quality improvement program and initially likely 100% quality assurance review of all ultrasound scans and decisions made by providers based on the scans. Medical directors must have appropriate training themselves and ultrasound skills in order to review, educate, and improve provider use of ultrasound. Protocol development is key to any ultrasound program and must take into account which scans will be performed, how they will be interpreted, and the safe limits to which ultrasound will be applied.

Conclusion

Each department must consider the significant costs associated with implementing new technology and balance this against the size of the potential patient population who would benefit from a specific ultrasound guided study or procedure. For many departments, this evaluation would be in favor of not implementing an ultrasound program. An engaged medical director is also necessary to ensure appropriate oversight and quality improvement processes are in place. There is a paucity of high quality literature evaluating ultrasound in the prehospital environment and immense opportunity for interested researchers.

© Springer Nature Switzerland AG 2021

B. D. Nicholson et al. (eds.)Manual of Austere and Prehospital Ultrasoundhttps://doi.org/10.1007/978-3-030-64287-7_3

Helicopter Emergency Medical Services

Katherine Rodman¹   and Matthew Jensen²  

(1)

Department of Emergency Aviation, VCU Health, Richmond, VA, USA

(2)

VCU Health Critical Care Transport Network, Richmond, VA, USA

Katherine Rodman (Corresponding author)

Email: [e-mail]

Matthew Jensen

Email: [e-mail]

Keywords

Air medicalRotary wingHelicopterHEMSCritical care transportUltrasoundPOCUSDiagnosticsDecision-making

Approximately 85 million Americans live more than 1 hour away from a level one or level two trauma center [1]. In order to serve these disparate and geographically isolated communities, the use of helicopter emergency medical services (HEMS) has become ubiquitous in the United States. Whilst the proliferation of HEMS has become controversial in recent years, the utilization of rapid transportation to definitive care can, and has been, lifesaving for innumerable patients. Broadly speaking, civilian HEMS is used for two reasons. Firstly, the speed at which the patient can be moved from either the scene of an accident or critical access hospital to a regional specialty or trauma center. Secondly, the ability of the critical care providers on the helicopters to bring hospital-level care to the patient, thus accelerating the patient’s care timeline [2].

It is estimated that there are 400,000 rotary wing medical transports each year in the United States, utilizing a wide range of different single-engine and multi-engine airframes [3]. The most commonly employed airframes for HEMS in the US include single-engine Bell 206/407, and Airbus’s AS-350 and EC-130, and multi-engine platforms Bell 222/230/412/429, Airbus BO-105/BK-117/EC-135/EC-145/AS-365, and the Agusta A-109/139 [3]. The decision to choose one airframe over another is born out of geographical, topographical, mission profile, and financial considerations.

The program the authors work for utilizes an Airbus EC 135 and EC145 to carry out approximately 1300 scene and interfacility flights per year. These aircraft are staffed with a single pilot, critical care registered nurse, and paramedic and carry a single patient in a combination of visual and instrument flight rules missions. The interior of these two aircraft features two-rear facing seats with an optional configuration of a third aft forward-facing seat on the patient’s left. The onboard inverter provides direct current power for medical equipment, including a mounted Hamilton T1 ventilator, Zoll Propaq MD cardiac monitor, and multiple Braun BodyGuard infusion pumps. The advanced critical care equipment on board also includes a cooler containing an Abbott iSTAT device with point of care laboratory testing supplies, and a TIC cooler containing packed red blood cells. These pieces of equipment, whilst important for delivering tailored patient care, all consume valuable space within the cabin.

There are several significant potential or perceived benefits to the use of point of care ultrasound (POCUS) in HEMS. Most intuitively is the ability for flight crews to utilize the technology to identify the presence of traumatic injuries or medical and surgical pathology that may require intervention and treatment urgently to preserve life or reduce the likelihood of morbidity and mortality. Clear examples of this would be the presence of blood in Morrison’s Pouch following blunt trauma necessitating transfusion of blood products, the absence of lung slide in a patient about to be converted to positive pressure ventilation and so requiring pneumothorax decompression to prevent tensioning, or a developing pericardial tamponade requiring ultrasound-guided pericardiocentesis to stave off cardiac arrest. The use of ultrasound has been validated as being highly sensitive and specific for internal hemorrhage when used by trained providers [4, 5].

Similarly, the use of ultrasound in the flight environment can provide clinical information that allows for the earlier diagnosis of critical pathology. Historically, the ability to see inside a patient and visualize causative pathology has been the purview of hospitals alone, but the migration of small, portable, and affordable ultrasound devices outside their four walls has made it possible to make diagnoses much earlier. The acceleration of an informed diagnostic process to the prehospital environment may bring about more nuanced and tailored patient care. This is exemplified by the hypothetical hypotensive and tachycardiac patient. It may reasonably be assumed that the patient is hypotensive secondary to volume loss, either severe dehydration or internal bleeding, and that the heart rate is compensatory and beneficial. By performing a Rapid Ultrasound in Shock and Hypotension exam or similar, it may be revealed that the patient is actually suffering from a profound aortic dissection and that the key to them surviving transport to hospital is decreasing the percussive impact of systole against the dissecting lumen through the use of beta blockade. In this example, the use of ultrasound in the HEMS environment would transform the treatment decision made by the flight crew and directly impact patient care.

Unlike interfacility transfers where HEMS are facilitating the transport of a patient between sending and receiving physicians and hospital units, scene requests require flight crews to attend an oftentimes undifferentiated patient and then choose the appropriate facility to deliver them to for definitive care. This decision can be challenging as closer, non-specialty facilities may not be appropriate for certain conditions, to include stroke, myocardial infarction, and trauma. The role of HEMS is to provide advanced critical care to patients whilst rapidly transporting them to the most appropriate facility, and as such this may require overflying closer hospitals. Ultrasound can play a role in assisting this decision making, as the patient with a grossly positive eFAST following a motor vehicle accident may potentially be better serviced by a longer flight time that terminates at an American College of Surgeons accredited level one trauma center, rather than a closer level two or three trauma center.

The introduction of POCUS into the HEMS environment can add another layer of procedural assistance during transport. Whilst the gold standard for confirming placement of endotracheal tubes (ET) has been established with the use of end tidal CO2, the utilization of ultrasound as an adjunct to EtCO2 for ensuring correct ET placement has been demonstrated to be a valid confirmation tool by flight crews, and may have additional benefit in low cardiac output states, hypothermia, or large pulmonary embolism [6–8]. Additionally, ultrasound has been shown to aid providers in establishing vascular access in vasculopathic patients [9, 10]. As the population ages, and their comorbidities increase, the ability to quickly and easily achieve intravascular access in an ill patient may decrease. For the difficult vascular access patient in a life-threatening situation the use of intraosseous access has increased in prevalence, though this procedure may not always be appropriate or indicated. In these situations, using the linear probe on the ultrasound may enable providers to access vasculature that is deeper within tissues and administer intravenous therapy without the trauma and potential sequalae of intraosseous access.

When consideration is given to implementing any new device, equipment, or technology, the balance of possible advantages must be weighed against the possible disadvantages the introduction may bring. Whilst the potential gains ultrasound can bring to HEMS are myriad, the corresponding potential losses stack up in equal number. The most immediately obvious is the space within the patient-care cabin that the device occupies. The Commission on Accreditation of Medical Transport Systems requires that all equipment be secured within the cabin to reduce