Prehospital Ultrasound: Emerging technology for EMS

Prehospital ultrasound is a form of medical imaging that is portable, non-invasive, painless, and does not expose the patient to ionizing radiation. With proper training and education, prehospital providers can use ultrasound to obtain immediate anatomical, diagnostic, and functional information on their patients [1].

In recent years, ultrasound devices have decreased in size and cost while producing images of enhanced quality. The recent advances in bedside devices have made ultrasound more accessible to prehospital providers with the introduction of field ultrasound devices that are more affordable, smaller in size, durable, lightweight, and with high-resolution imaging quality.

Prehospital ultrasound may be beneficial in the diagnosis and management of critically ill patients [2,3,4,5,6,7]. EMS providers can apply training to interpret ultrasound scans with a high degree of accuracy in a relatively short period of time [5,8].

For example, prehospital focused abdominal sonography for trauma (FAST) exams have the potential to provide valuable information in abdominal trauma with high reliability leading to more appropriate transport destination decisions [9,10,11]. In addition, field ultrasound images can be transmitted enroute to the emergency department to facilitate further evaluation by ED physicians and trauma surgeons to expedite care [12,13,14].

Prehospital ultrasound has been widely adopted in most states and around the world with a continuously growing list of diagnostic applications [5,6]. The enhanced technology enables prehospital professionals to answer focused clinical questions, which translate into faster and more accurate diagnosis and care of patients presenting with time-sensitive emergency conditions [2,3,4]. Better outcomes have been reported with the use of prehospital ultrasound [2,5,6,15,16].

Bedside ultrasound is well accepted by patients and has shown to improve patient satisfaction [17]. However, like any other nontraditional intervention, the addition of field ultrasound raises several questions in terms of potential clinical applications, feasibility, training requirements, cost, and more importantly its impact on the care process and patient outcome.

Clinical applications for field ultrasound
In EMS systems with regionalized trauma care and field triage guidelines, field ultrasound offers earlier detection of time-critical conditions that may require deliberate transport to an accredited trauma center, chest pain center, stroke center, or pediatric specialty care facility. There is an abundance of clinical applications for the use field ultrasound discussed in the literature with varying degrees of benefit:

1. Causes of dyspnea
Field ultrasound increases the accuracy of diagnosing pulmonary edema versus chronic obstructive pulmonary disease as the cause of acute dyspnea [1,18,]. It is effective in patients with unexplained hemodynamic instability to help differentiate between cardiac and non-cardiac causes of shock [18,19]. In some limited cases the potential of field ultrasound to detect massive pulmonary emboli in patients has been demonstrated [15,20].

2. Recognizing OB emergencies
Although advanced training is necessary, some prehospital providers have shown that ectopic pregnancy, placenta previa, and placenta abruption can be identified with about 95 percent reliability [4,21,22].

3. Cardiac evaluation and resuscitation
Specialized prehospital resuscitation protocols using ultrasound have shown that in patients undergoing CPR, ultrasound helped prehospital providers determine cardiac wall motion when the initial ECG diagnosis was identified as asystole [23]. This was associated with an increased survival to hospital admission [24].

In addition to cardiac motion, ultrasound helped differentiate between true PEA — electromechanical dissociation — and pseudo-PEA — coordinated electrical activity with no palpable pulse [23,24]. Pseudo-PEA was also associated with increased survival to hospital admission when compared with true-PEA [23,24].

In patients in a peri-resuscitation state, ultrasound improved the diagnostic accuracy for potential diagnoses of tamponade, profound hypovolemia, myocardial insufficiency (severe left and/or right ventricular dysfunction), or thromboembolism (pulmonary or cardiac) [25,26]. EMS systems with prehospital protocols that use asystole or PEA as criteria for field resuscitation termination can benefit from adding ultrasound to such protocols [23,25,26].

4. Airway placement confirmation and monitoring
Another diagnostic application of field ultrasound includes confirming endotracheal tube  placement through high-resolution detection [27]. Although waveform capnography is considered the gold standard for successful ETT verification, this method has some limitations in specific situations such as cardiac arrest, low cardiac output, acute pulmonary embolism, and hypothermia [28].

Ultrasound offers prehospital professionals an alternative method for ETT confirmation for recognizing tube displacement or differentiating between main tracheal intubation and right mainstem intubation [27,28,29,30,31]. For example, Adi et al's (2013) study showed an impressive result of 98.1 percent accuracy in initial verification [30].

5. Gastric tube placement confirmation
Gastric tube placement — nasogastric or orogastic — remains a recommended critical care intervention for all intubated patients as it decreases the risk of aspiration and improves tidal volume. Some EMS systems that place gastric tubes report that placement is easily confirmed using field ultrasound [32].

6. Fracture determination
Many types of suspected long-bone fractures are managed in the prehospital setting. Growing evidence suggests that use of field ultrasound can successfully identify several types of long bone fractures [33,49,50].

7. Prehospital needle thoracostomy placement
Prehospital ultrasound use in trauma patients with suspected pneumothorax can be effective in preventing unnecessary field needle thoracostomys [34,35]. One study showed that when thoracic ultrasound was used to detect pneumothorax, only 26 percent of the patients were actually found to not have a pneumothorax [34,35,36,37]. Using field ultrasound could help decrease potentially unnecessary needle thoracostomys and other invasive procedures en route to hospital [38].

8. Peripheral intravenous access
Establishing vascular access is one of the most common procedures performed in the prehospital setting and on occasion is a high priority for the critically ill and unstable patient. The condition of the patient often presents challenges in attaining intravenous access. Conditions associated with difficult vascular access include very young age, obesity, chronic illness, IV drug abuse, and hypovolemia to list a few [39,40,41].

Patients with difficult IV access are often subjected to repeated attempts as in some cases time to IV placement can affect optimal resuscitation of the critically ill patient. Ultrasound guided IV access has shown to increase the success rate and decrease complications [42,43,44,45,46,47,48].

9. Stroke diagnosis
It is well discussed in the literature that improving the outcome of stroke patients requires early and rapid time-sensitive diagnosis and treatment as well as transport to an accredited stroke center. Early diagnosis using telestroke protocols with field transcranial ultrasound for stroke diagnosis has shown to decrease diagnosis-to-fibrinolytic therapy times and expand the use of special interventional radiology procedures [51,52,53].

Practice challenges for field ultrasound
Widespread adoption of field ultrasound in the United States has been limited due to several factors. The most commonly reported barriers to field ultrasound implementation include, but are not limited to, cost, training deficits, short transport times, concerns about delaying time to definitive care, lack of evidence, approval by EMS administration, buy-in by medical directors and ED staff, and acceptance by veteran EMS providers [1,52,54].

In most cases initial ultrasound education and training is possible with relatively short training courses. Like any other clinical skill, ultrasound competency requires practice, ongoing education, and quality management programs with physician oversight [55,56].

Future direction
Prehospital emergency ultrasound has many clinical applications that can potentially reduce patient morbidity and mortality from life-threatening emergency conditions. The potential for the evolution of field ultrasound is largely dependent upon developing a growing body of prehospital data that demonstrates its safety and effectiveness in clinical procedures and timely diagnosing medical and trauma conditions.

Above all, the value of ultrasound use in the prehospital setting must illustrate how it improves patient outcomes. This could be facilitated by enhancing the technology of telesonography for real-time assistance with interpretation of ultrasound images by physicians [43,57]. Also, developing effective ultrasound training programs for different level providers is important to maximize its use. In addition, a cost-benefit analysis for prehospital ultrasound must be entertained.

One area of future research must include the early ultrasound diagnosis of ischemic stroke in the prehospital setting to improve time to thrombolysis. Hopefully, this research will correlate into better neurologic outcomes of stroke affected patients [53]. Considering the growing areas of mobile integrated healthcare and community paramedic programs, one cannot anticipate the endless possibilities that prehospital ultrasound could offer these diverse community healthcare services [58].

 

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