The concept of MARCH was developed by the Special Operations Forces in 1996 and has remained unchanged in Tactical Combat Casualty Care and Advanced Trauma Life Support, which outlines the preventable causes of death as follows:

This remains the systemized approach that prioritizes life-threatening interventions.

• Intubation: While presenting both sides of the evi­dence, pros and cons, for advanced airway manage­ment, it is most important to understand the limitations of a studies design, and the correlation

• Metrics: They need to correlate to benchmark trig­ger times for skills, add objective measures like capnography with intubation or BVM ventilation, and record the success or failure for each critical skill performed prehospital. This data is then run with outcome data to determine competency in the eld.

Well-resourced EMS systems often take an organized and systematic approach to POCUS.This approach includes the development and implementation of POCUS algorithms for the prehospital setting. These protocols have adapted the FAST exam, combined components of separate exams to dif­ferentiate shock and cardiac arrest, and dened methodology for evaluating a mother and fetus.

The Prehospital Focused Assessment with Sonography in Trauma (PFAST) was adapted from the hospital FAST exam. Paramedics in a German multi-center study were able to com­plete scans on 90% of patients prior to hospital arrival with a 93% sensitivity for intraperitoneal hemorrhage [14]. All para­medics reported that PFAST played a crucial role in team decision-making, with 33% describing changes in on-scene trauma management and 20% noting change in receiving hos­pital. When a negative exam can be obtained in minutes and a positive exam in only seconds, this protocol requires a small investment for potentially large returns in team dynamics.

The Rapid Ultrasound for Shock and Hypotension (RUSH) exam is a three-step algorithm described by Perera

The prehospital environment can be unpredictable and poses challenges to healthcare provision. POCUS has demon­strated utility as an adjunct to the physical exam, supplement to the current diagnostics, and aid to the paramedic’s medical decision-making. Physical examination is fallible when compared to the more controlled environment of the hospi­tal. For providers obtaining pulses on patients in cardiac arrest, studies have demonstrated that manual carotid assess­ment is unreliable even in the more controlled setting of the hospital [23, 24]. Prolonged pulse-checks delay chest com­pressions and can decrease survival rates [25]. Conversely, false identication of an absent pulse may result in unneces­sary CPR and resuscitative medications, which have been associated with poor neurological outcomes [26]. POCUS has helped discern cardiac contractility when the physical exam is equivocal, a scenario not uncommon with the addi­tional challenges of the prehospital environment [1, 5, 6]. Additionally, one random-controlled trial demonstrated that carotid compressibility on ultrasound, a “POCUS pulse­check,” had greater rst-attempt reliability than manual assessment in obtaining pulses [27].

22]. Studies have projected that up to 86% of cardiac arrest

The advantages of ultrasound in rural regions are signi­cant enough that the limitations may not be immediately apparent. However, discussing limitations will help identify how POCUS can improve to accommodate remote and some­times austere environments. The rst limitation of ultrasound in remote areas is that skilled operators are scarce in rural and less economically developed communities. Performing and interpreting ultrasound is a skill that, without training, is use­less in practice. Different groups and organizations focus on training local healthcare providers because few of the local providers have prior training or experience [41–44]. Another limitation to accessing ultrasound technology for rural regions is lack of equipment. Even though ultrasound technology is becoming less expensive and more available through mobile computing technology, poorly funded areas still may have only one instrument in an entire hospital or for an entire patient population. The Tanzanian midwives that were inter­viewed, despite possessing a Doppler ultrasound device, often resorted to a fetoscope because the only hospital Doppler ultrasound was being used for a different patient [34]. Furthermore, austere environments come with their own set of challenges for maintaining and servicing ultrasound equipment. High altitudes, lack of electricity and/or WIFI, extreme temperatures, dirt oors, humidity, sea water, and other environmental hazards may harm the delicate electron­ics in ultrasound devices. Repairing the device would require delivery or travel to a servicing facility, the receipt of a servic­ing professional on- site, or additional servicing training for the healthcare provider, each of which are inconvenient and costly options for a remote community [38].

With the advent of the Space Force and the increasing private sector of space exploration, ultrasound is nding its place among standard medical equipment on space shuttles. The speed and clarity of relayed images in low orbit make the tech­nology practical for telemedicine guidance from ight surgeons at mission control [53]. Ultrasound has allowed for versatile imaging on the International Space Station (ISS), and hand-held models are currently being tested [54]. With limited weight and volume capacities requiring judicious selection of cargo, this transition to POCUS would be ideal. Sonography has been employed clinically on the ISS, largely in evaluation of ophthal­mologic, musculoskeletal, and vascular complaints. Ocular changes associated with spaceight have been well- documented, including globe attening, cotton wool spots, choroidal folds, retinal thickening, and hyperopic shifts [55]. Ultrasound has been used to evaluate optic nerve sheath diameter and central retinal artery blood ow of crew members to conrm expected microgravity shifts and rule out the need for intervention, which could compromise a mission [54]. Microgravity also affects the musculoskeletal system through gravitational unloading of intervertebral disks, redistribution and alteration of muscle, and demineralization of bone [54]. These effects decrease strength and increase the likelihood of trauma during—and after—a mission. Ultrasound has been used to evaluate the integrity of the multidus and erector spinae muscles, as well as discern a grade 1 biceps femoris tear. In the latter scenario, an astronaut on the ISS experiencing an injury during physical conditioning was suspected of having a ruptured biceps femoris. However, ultrasound revealed only a minor tear, which decreased the degree of management required [54].

Arguably the most signicant clinical use of sonography in space ight medicine occurred when an astronaut with a prominent left external jugular vein was examined. Ultrasound imaging demonstrated an obstructive venous thrombosis in the left internal jugular vein, the scans of which allowed for a multidisciplinary collaboration on opti­mal therapy. After evaluating the risks of thromboembolism versus anticoagulation without reversal agents aboard the station, an enoxaparin regimen was initiated until apixaban, protamine, and prothrombin complex could be delivered to the station. The plan of care was successful, demonstrating the efcacy of ultrasound in team-driven surveillance, diag­nosis, and healthcare during spaceight [56].

Trauma can result in a variety of musculoskeletal com­plaints, and high-frequency linear array ultrasound could be a valuable adjunct in evaluation, stabilization, and pain man­agement [28]. While life-threatening injuries typically indi­cate resuscitative efforts and rapid transport, lower acuity patients may benet from additional evaluation and care on­scene. POCUS can discriminate between pulsatile hema­toma, pseudoaneurysm, and aneurysm, which may lead to different treatment algorithms. It can also detect hernias, guiding reductions for patient comfort and incarceration pre­vention. If physical exam is limited by body habitus, swell­ing, or patient tolerance, ndings on ultrasound can safely, reliably, and inexpensively discern the etiology [28]. The hypoechoic foci of tendon and ligament tears differ from arthropathic uid collections; soft tissue inammation dis­tortion differs from the cortical disruption in bone fractures. Understanding the source of musculoskeletal pain is crucial to patient care and can help assess whether mild therapy is appropriate or more signicant intervention is required, such as long-bone fracture protocol at a trauma facility. Furthermore, POCUS can guide fracture reduction by avoid­ing neurovascular compromise during bone alignment.

This increased imaging capability may expand therapeutic options in remote or military environments, as the diagnostic adjunct can also guide eld musculoskeletal procedures necessitated by scarce medical assistance. Procedures such as arthrocentesis, foreign body localization and removal, steroid injection, nerve block administration, and other interventions have been performed in hospital. Appropriate training could adapt these techniques to remote environments, where patients have signicant needs but limited options. Nerve blocks may be especially useful for long transports and manipulative procedures, providing improved localized pain control without the adverse effects of narcotics.

Vascular evaluation and access are an integral part of pre­hospital emergency care, and POCUS could expand the scope of practice and quality of care provided by paramedics. The use of ultrasound-guided intravenous cannulation is a useful tool for peripheral vascular access in patients with challenging body habitus. When in-hospital ultrasound guidance was compared to palpatory methods of peripheral intravenous cannulation, ultrasound guidance had a greater success rate (97% vs. 33%), shorter completion time (13min vs. 30min), fewer percutane­ous punctures (1.7 vs. 3.7), and greater patient satisfaction [57]. Prehospital obstructions to peripheral vascular access may exceed those of the hospital environment, yet ultrasound guid­ance is not a common practice in EMS systems. Using either static or dynamic technique, POCUS can be used to gain access to femoral, jugular, subclavian, or peripheral veins, as well as

Ultrasound has been utilized for ophthalmologic com­plaints of foreign body, globe rupture, lens dislocation, vitre­ous hemorrhage, and detached retina. While most of the prehospital utility in these evaluations would come from a more rapid notication of ophthalmologists and surgeons, promising trials have used sonography to assess intracranial pressure (ICP) [22]. Optic nerve sheath diameter measure­ments with ultrasound have a high sensitivity for elevated ICP, and are a quick, non-invasive alternative to waiting for a lumbar puncture or CT scan. Positive ndings would guide prehospital care on scene, as well as communications to the appropriate providers during transport, ultimately circum­venting time-consuming and expensive diagnostics on arrival.

Although ultrasound often comes to mind for obstetrics, the imaging modality is also useful in evaluating the male reproductive organs. Testicular trauma may involve contu­sion, obstructive hematocele, fracture, torsion, hernia, or dislocation. Both B-mode and Doppler are useful in discern­ing the injury location and severity, which can provide sur­gical teams advance time to prepare for emergency interventions such as decompression, orchiopexy, and repair. Quick activation of the surgical team is important to prevent permanent damage or sterility, and POCUS could facilitate this critical action [70].