Key Points
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After World War II, the subspecialty of prehospital emergency medicine evolved with leadership from doctors in anesthesiology. In many countries, prehospital emergency medicine is considered the fourth pillar along with anesthesiology, critical care, and pain therapy.
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Emergency medical service (EMS) systems differ among and within countries. When these differences were put together, two primary models evolved. In the United States, paramedics provide prehospital care for all patients (single-tiered system). In many European countries, EMS-physicians lead the prehospital care for patients requiring advanced life support (two-tiered system).
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The core approach of managing prehospital emergencies involves basic life support and advanced life support.
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Rapid, simultaneous assessment and triage form the cornerstone of prehospital care—the use of a primary survey and limited diagnostic adjuncts can ensure transport to the most appropriate care setting.
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In major trauma, prehospital care must limit the time spent on the scene, control hemorrhage, and expedite transport to a trauma center, ideally via a rescue helicopter. Although this approach has been used both in the military (e.g., Vietnam) and in civilian locations, it is not always possible. Prehospital intravenous fluid resuscitation for major trauma varies in approach. Patients with penetrating torso injuries and hemorrhagic shock may benefit from limited intravenous fluid resuscitation and permissive hypotension, in particular in urban settings. Prevention of the lethal triad of hypothermia, acidosis, and coagulopathy is of paramount importance.
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In acute coronary syndrome and stroke, achieving rapid reperfusion of the ischemic tissue is the priority. Because only specialized centers provide 24-hour cardiac catheter service or stroke teams, rapid transport to acute myocardial infarction or stroke centers is critical. In response to a myocardial infarction, morphine, oxygen, nitrates, and aspirin are the main components of prehospital therapy. Fibrinolysis for myocardial infarction has been used with significant success in the prehospital setting but requires very close supervision by EMS physicians.
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The future of EMS will likely see an increased use of telehealth, which can narrow the time gap between the hospital and the field. This will facilitate improved field and hospital diagnostics and treatments, and ensure more efficient handoffs when arriving at the receiving hospital.
Acknowledgment
The editors and publisher would like to thank Drs. Peter Nagele and Michael Hupfl for contributing a chapter on this topic in the prior edition of this work. It has served as the foundation for the current chapter.
Background
The heritage of the modern emergency medical service (EMS) can be traced to the late 1700s with the approach to triage and forward patient retrieval of Napoleon’s chief surgeon, Dominique Jean Larrey. Later, in 1832, in London, transport carriages were introduced for cholera patients. The rationale for the introduction of such carriages was that the “curative process commences the instant the patient is put into the carriage.” Americans adopted this concept during the American Civil War, when General Jonathan Letterman, a Union military surgeon, created the first organized system in the United States to transport injured patients. Civilian EMS systems in the United States evolved subsequently—with the first one forming in Cincinnati in 1865.
It was nearly a century later in the 1960s when changes in medical technology and knowledge joined forces with political will to formalize the concept of prehospital care. In the early 1960s, two major clinical advances occurred—cardiopulmonary resuscitation (CPR) for life support of the patient in cardiac arrest, and the development of portable external defibrillators. These two advancements provided the foundation of advanced cardiac life support (ACLS). This, in turn, led to the concept of trained community members to respond to emergencies to improve outcome.
In 1965, President Lyndon Johnson created the President’s Committee for Traffic Safety, which published the report Health, Medical Care, and Transportation of the Injured . It identified motor vehicle crashes as a significant public health concern. The committee recommended a national program to reduce highway deaths and injuries. Additionally, in 1966, a report was released by the National Academy of Sciences titled Accidental Death and Disability: The Neglected Disease of Modern Society . It emphasized the need to address the quality of prehospital emergency medical care as it recognized that ambulances were ill-equipped and inappropriately staffed.
These two documents paved the way for the Highway Safety Act of 1966, which was passed by Congress and ultimately led to the formation of the National Highway Traffic Safety Administration (NHTSA) within the Department of Transportation. The NHTSA developed a national EMS curriculum which, in 1969, became the standard for emergency medical technician (EMT) training in the United States. In 1973, Congress further passed the EMS Systems Act, granting funds for the development of regional EMS systems. As a result, various states established a total of approximately 300 EMS regions with associated federal support. In the United States, the responsibility of EMS then shifted from federal to state level in 1981, which created heterogeneity in the system.
During the same period of time, EMS and prehospital medical systems were similarly evolving in most developed countries outside the United States. All had unique aspects and points of difference, mostly influenced by the local geography, political will, origin, and resources. The fundamental mission of EMS systems remained common—to deliver the best possible prehospital care to the right patients, in the right timeframe, and to transport them safely to a higher level of care.
Some systems evolved to be predominantly staffed by physicians, while others were staffed almost exclusively by paramedics with no to very minor physician involvement, and most fell somewhere between the two—with at least the capacity for a combined physician-paramedic crew.
Basic Versus Advanced Life Support and Beyond
CPR was developed in 1960 when the American Heart Association started a program to train physicians in mouth-to-mouth resuscitation (expired air resuscitation) with associated external chest compressions. This led to the development of a tiered system: basic life support (BLS) and advanced life support (ALS) to denote the different skillsets of responders in an organized EMS.
First responders (such as police officers, firefighters, EMTs, and paramedics) are generally the first to arrive to an emergency and can provide medical assistance. A tiered system with different skillsets helps to make the scope of practice and role delineation clearer in the often chaotic prehospital environment.
Basic Life Support
The adult BLS sequence is circulation-airway-breathing (C-A-B). The goal is to ensure continuous blood (and by proxy, oxygen) supply to major organs. Firefighters, lifeguards, and police officers are often BLS certified because they are often the first to a scene and the application of BLS does not require specialized medical knowledge, per se.
CPR and the use of an automated external defibrillator (AED) are considered BLS skills and the increasing availability of automated defibrillators makes it ever more likely that “unskilled” members of the community will be the first to deliver defibrillation in the event of an out-of-hospital cardiac arrest (OHCA). BLS also includes simple airway maneuvers such as chin lift, jaw thrust, and oxygen administration. For trauma care, basic skills include airway management such as simple airway maneuvers, oropharyngeal and nasopharyngeal airways, and bag-mask ventilation.
Besides CPR and automated external defibrillation, BLS also includes hemorrhage control, and fracture and cervical spine immobilization. In the trauma patient who has suffered a primary traumatic cardiac arrest, CPR is unlikely to be of benefit and may, in fact, detract from useful life saving interventions. This relative controversy will be discussed later in the chapter. The decision not to perform CPR in the resuscitation of the arrested trauma patient should be made by personnel specifically trained at least at the ALS level—and probably only in advanced prehospital systems that include suitably skilled physicians or intensive care paramedics.
Advanced Life Support, Intensive Care–Level Prehospital Care
The knowledge and skills necessary to successfully perform ALS are built upon the firm foundations of BLS. For example, even the most experienced prehospital or trauma practitioner relies upon basic airway maneuvers to maintain oxygenation when more sophisticated techniques have failed.
In the prehospital environment, ALS is most often provided by paramedics (advanced EMT practitioners). In many jurisdictions, however, there is a level of prehospital care above ALS, and, outside the United States, combined physician-paramedic crewed helicopter emergency medical services (HEMS) are common. In places where doctors are not part of a HEMS response, paramedics with advanced and intensive care skillsets are often used. This enables the resuscitation bay to essentially be taken to the patient, and, in addition, for advanced resuscitation to be maintained throughout transport. The rationale for these advanced prehospital teams is to maximize the opportunity, while minimizing the time delay for delivery of the advanced trauma care that severely ill or injured patients need.
The provision of advanced, hospital-level interventions (e.g., advanced airway management such as endotracheal intubation, thoracostomy, resuscitative thoracotomy, and commencement of blood product transfusion) remain areas of significant controversy when applied to the prehospital environment. The question of whether it is better to prioritize caring for the patient in the field (“stay and play”) or to prioritize expedited transport (“scoop and run”) is an old and polarizing one. In environments where transport times are prolonged due to expansive distances (such as Australia), delivering advanced interventions early can be lifesaving. On the other hand, prolonging scene times and delaying presentation to definitive trauma care in order to initiate treatment in the field is unlikely to be in the patient’s best interest in other settings. In all mature trauma systems (incorporating the prehospital and in-hospital phases of care), a balance will need to be struck between these two competing priorities.
The reality is that on a population-wide scale, it is rare for anyone to need the advanced services of an EMT, let alone an HEMS prehospital resuscitation team. It is difficult, therefore, to adequately power a study to show a difference between the various models of prehospital care, if such a difference exists. As such, individual prehospital and in-hospital trauma systems have adapted to fulfill the perceived requirements of their population and account for areas of operational limitation.
Training for ALS EMTs now requires a rigorous educational background, and includes skills in advanced and invasive monitoring, diagnostics, and management. Systems functioning at or above the ALS level provide a more comprehensive assessment and stabilization of the trauma patient. In the United States, providers certified at the paramedic level (EMT-P) can perform any of these interventions, whereas providers certified at the intermediate level (EMT-I) may perform a select subset of these skills. Other jurisdictions have comparable delineations of skillset.
Emergency Medical Technician and Paramedic-Based Emergency Medical Service Systems
Specially trained EMTs and paramedics form the bulk of the workforce of EMS systems in North America and in many other developed nations. Under U.S. law, physicians, functioning as EMS directors, are required to approve the medical operations of the EMS systems they oversee. This includes communication, clinical operations, and governance.
In the United States, there are three levels of EMTs based on their level of education and training: EMT-basic (EMT-B), EMT-intermediate (EMT-I), and EMT-paramedic (EMT-P). The primary focus of the EMT-B is to provide basic emergency medical care (using BLS skills) and transportation to a healthcare system. They typically staff nonemergency ambulances and may also respond to nonemergency calls. EMT-I practitioners, or advanced EMTs, provide basic and limited advanced emergency medical care and transportation. They are regulated differently and their skills range between BLS and ALS depending on state regulations. EMT-P is the highest skillset within EMTs in the United States. They undergo intensive 1- to 2-year training in advanced prehospital emergency care. They are ALS trained and can perform procedures such as endotracheal intubation, administration of drugs, and manual defibrillation.
In many other countries, paramedics are required to complete bachelor-level university degrees and are nationally or regionally registered by regulatory bodies—in a similar way that medical practitioners are licensed. In some regions, such as in most states of Australia and in many countries in Western Europe, intensive care paramedics have advanced skills in complex medical and trauma management as well as casualty access and rescue skills.
Primary Survey and Initial Assessment at the Scene
The primary survey is usually performed in the same ABCDE (airway-breathing-circulation, disability-exposure) mnemonic format that is widely known from ACLS. Since 2010, the American Heart Association has recommended changing their ABC approach (airway-breathing-compressions) to CAB (compressions-airway-breathing), emphasizing circulation prior to airway. This is particularly relevant for someone in cardiac arrest to bring focus to chest compressions. It is also relevant to the trauma patient suffering critical bleeding. If you can hear the bleeding, you should stop it first!
The approach, therefore, in the prehospital major trauma patient is C-ABCDE. Strategies for prehospital management of critical hemorrhage are discussed in more detail elsewhere in the chapter, but broadly, options include direct pressure, deep wound packing, use of novel hemostatics (there are several on the market), and tourniquets for extremity hemorrhage (the Combat Application Tourniquet [CAT] is the most widely used). Specific techniques can be used for major maxillofacial hemorrhage, which include nasal packing, or balloon tamponade devices (such as the Rapid Rhino), dental splints, and immobilization of the jaw with a hard, cervical spinal collar.
Novel approaches using resuscitative endovascular balloon occlusion of the aorta (REBOA) to manage critical bleeding in pelvic trauma in the absence of chest trauma are not yet widespread. Indeed, prehospital REBOA has been used successfully on only one documented occasion by London’s Air Ambulance. It remains an area of significant controversy and of limited evidence.
Once critical bleeding has been identified and temporarily controlled, moving through the remainder of the primary survey in a rapid yet methodical way is warranted. If there is airway (A) obstruction, the obstruction should be cleared and the airway secured if necessary. While it will often be appropriate to perform a rapid sequence intubation in the prehospital environment, it may not always be necessary or beneficial. A balance must be struck between delaying transfer, likely disposition once in hospital, distance to definitive care, and skillset available. Most prehospital services continue to secure the cervical spine with a hard collar for transport and this would be applied at this time.
Breathing (B) becomes the next priority; after the airway is cleared and possibly secured, a patient’s breathing is assessed by observing respiratory rate, pattern, and degree of chest rise and fall. Supplemental oxygen and assisted ventilation may be indicated. Immediately reversible causes of potentially fatal chest trauma, such as tension pneumothoraces, may also be identified and treated with minimal delay to patient transfer. In the case of tension pneumothoraces, many advanced prehospital services (especially those with medical-paramedic HEMS crews) have adopted a finger thoracostomy approach to chest decompression, rather than needle thoracostomy, to achieve a more definitive endpoint early and minimize the risk of reaccumulation of the pneumothorax in transit. Of course, this definitive care may not be available prehospital in all jurisdictions.
Circulation (C) is next assessed by palpating pulses, checking for heart rate, pulse quality and regularity, measuring blood pressure, and again assessing for sources of hemorrhage. As an approximation, a palpable carotid pulse corresponds to a systolic blood pressure of at least 70 mm Hg, and a palpable radial pulse to a systolic blood pressure of 80 to 90 mm Hg.
Also, as part of the primary survey, large-bore intravenous access is obtained. Early fluid management in the trauma patient has been a contentious issue in trauma management for many years. There has been much discussion in the scientific and prehospital literature in relation to the role of crystalloid fluid in the early resuscitation of the trauma patient. Over the past decade there has been a significant shift away from the aggressive use of crystalloid and a shift toward early administration of blood products in the prehospital environment. Some prehospital retrieval services carry red cells only, whereas some (particularly in the United Kingdom) also carry freeze-dried plasma products. In the trauma patient with no concomitant head injury, achieving a systolic blood pressure of 90 mm Hg is ideal (so-called “permissive hypotension”). The only caveat to this blood pressure target is in the head-injured patient. If head injury is present or suspected, then hypotension should be avoided. Indeed, available evidence suggests that in the presence of severe head injury, a single episode of systolic hypotension below 90 mm Hg may double mortality.
As part of the assessment of circulation, suspected long bone fractures can be immobilized with CT-6 (or equivalent) splints and the patient may be packaged in a vacuum mat for transport. If the prehospital team has the capability and expertise, an extended focused assessment with sonography in trauma (e-FAST) exam can be performed as part of the circulatory assessment. This may assist in identifying pneumothoraces before transport and may also reveal other major sources of bleeding that can be relayed to the receiving center.
Disability (D) is measured using the Glasgow Coma Scale (GCS). The GCS is made up of three parts: eyes, verbal response, and motor response. The best patient response is recorded. In the GCS, a maximum of 4 points are allocated for eye opening, 1 being unresponsive and 4 being eyes open; a maximum of 5 points are allocated to verbal response, with 1 being unresponsive and 5 being alert and oriented; and a maximum of 6 points are allocated to motor response, with 1 being unresponsive and 6 for the patient who obeys commands. The highest possible score is 15 and the lowest score possible is 3. As a general rule, patients with GCS score of 8 to 9 have alteration in their conscious state significant enough so as to no longer have the ability to protect their own airway. Assessment of exposure and environment (E) and measures to defend core body temperature completes the primary survey and patient packaging process.
It is important to note that the management of the trauma patient in the prehospital environment relies on concurrent activity within the team. The key to prehospital diagnosis and treatment is the initiation of important treatment as problems are identified, while minimizing unnecessary time spent at the scene. The focus of professional prehospital teams is avoiding the “therapeutic vacuum,” or time where nothing useful is happening for the patient.
On arrival, and having assessed the scene, the prehospital care team must rapidly obtain a relevant and focused history of the patient and the events surrounding the incident. In the case of trauma, the ATMIST and AMPLE mnemonics provide a useful framework for gathering key initial information. ATMIST stands for age, time of incident, mechanism of injury, injuries sustained, vital signs (initial and subsequent), and treatment given so far. The AMPLE approach can then be applied to gather specific and relevant history. AMPLE stands for allergies, medications (regular and acute), past history, last meal (menses, tetanus injection) and the events surrounding the injury.
Monitors
Standard monitors in the prehospital setting include pulse oximetry, noninvasive arterial blood pressure monitoring, electrocardiography (ECG), temperature, and capnography. Indeed, the standards of patient monitoring in the mature EMS or prehospital retrieval service are as high as in most critical care areas of a major hospital. The main difference, of course, is that the monitor display itself must be capable of withstanding the environmental rigors of the prehospital environment, be easily carried, and have a long battery life. There are many commercially available monitors (and ventilators, infusion pumps, and other equipment for that matter) that are approved for flight and designed to be robust across a range of transport platforms and environmental extremes.
Point of Care Ultrasound
Portable and affordable ultrasound machines now make point-of-care (POC) ultrasound in the prehospital setting common. In Europe, the United Kingdom, and Australia, where physicians are active in the prehospital management of patients, this becomes even more practical to use. A Dutch observational study showed that 61% of ultrasound examinations impacted decisions in 88% of patients both in prehospital and once they reached definitive care. POC ultrasound is not limited to cardiac arrest; as mentioned earlier, abdominal ultrasound has also been shown to impact treatment decisions and in experienced hands, does not significantly delay treatment.
Out-of-Hospital Cardiac Arrest
Survival from sudden cardiac arrest is highly dependent on early CPR and early defibrillation. Communities have placed an increasing emphasis on bystander CPR, community accessible AEDs, and rapid response of EMS providers.
When the EMS arrives on the scene, the “Universal Treatment Algorithm” is started. Chest compressions continue until cardiac monitoring is placed and it is determined whether defibrillation is appropriate. Pharmacotherapy and airway management remain poorly defined. Optimal airway management in OHCA has not been established, and studies have shown that resuscitation with medications increases likelihood of the return of spontaneous circulation (ROSC) without improved outcome.
The likelihood of ROSC will depend in large part on the etiology of the cardiac arrest as well as the presence of adequate bystander CPR. By far the most common cause of OHCA is from cardiac pathology.
Acute Coronary Syndrome
Over 5.5 million patients in the United States present to emergency departments with chest pain as their primary complaint. Almost 50% of these patients arrive by ambulance. Any mature EMS system needs to be well equipped to manage this common and potentially life-threatening presentation. For a patient presenting with chest pain in the prehospital setting, three things need to happen: (1) diagnosis be made, (2) treatment commenced, and (3) triage to facility.
Prehospital Diagnosis and Electrocardiography
The prehospital ECG is essential in the assessment and triage of patients with chest pain and making the diagnosis of ST-segment elevation myocardial infarction (STEMI). It has been shown through multiple studies that prehospital ECGs are not only technically feasible but they also decreased the time from presentation to reperfusion. This finding has been replicated in rural settings. A recent study looking at clinical outcomes with use of prehospital ECGs showed that the adjusted risk of mortality was lower in cases where ECGs were used.
Prehospital Treatment and Fibrinolysis
Primary percutaneous coronary intervention (PCI) is the treatment of choice for STEMI patients if this therapy can be performed within 90 minutes of onset or less. When a patient is unable to receive mechanical reperfusion within that time window (either because of geographic isolation or arrival at a non-PCI community hospital) then evidence supports the use of fibrinolysis followed by PCI within 24 hours. It was subsequently demonstrated that a paramedic-based prehospital fibrinolysis program was practical and feasible in reducing time to treatment with favorable clinical outcomes.
Mechanical Circulatory Support
Prehospital Extracorporeal Cardiac Life Support
Recently extracorporeal cardiac life support (ECLS) has been introduced to the prehospital environment for treatment of OHCA patients in some very select settings. The use of mechanical ECLS in the prehospital setting remains controversial. Whether initiated in the field or in the emergency department, there is insufficient evidence to guide broad-based adoption of this practice. Multiple case reports have demonstrated some utility, but this therapy should not detract from high-quality ACLS.
Respiratory Distress
Respiratory distress is a common complaint necessitating prehospital medical intervention. Management requires rapid identification of emergent conditions and subsequent intervention to prevent further deterioration. Unfortunately, dyspnea, the perception of respiratory distress, can be influenced by a variety of factors and patient complaint alone is insufficient to identify the underlying cause or its severity. Early stabilization of respiratory function regardless of the underlying pathology is important to avoid significant morbidity and mortality. Even for anesthesiologists who are not participating in prehospital care, it is important to have a familiarity with these conditions as emergent or urgent surgical patients may present with dyspnea that is not fully evaluated and their initial management will fall on the anesthesia team in the perioperative period.
Evaluation
Initial evaluation of the patient in respiratory distress is structured to identify patients at risk for rapid progression to respiratory failure and identify the need for invasive support. Respiratory rate is an easily obtainable vital sign, and a rate of more than 30 breaths per minute would be defined as abnormal. It is important to consider that other factors, such as anxiety and intoxications, can affect the respiratory rate. Other physical signs include stridor, upper airway obstruction, inability to speak in full sentences, and cyanosis. Pulse oximetry has emerged as a standard monitor for detecting hypoxemia, although it should be noted that a patient can have significant respiratory pathology while maintaining a clinically acceptable oxygen saturation. Developing a differential of dyspnea can be challenging but may be simplified if the clinician considers the underlying organ system likely to be the culprit. Table 67.1 provides a comprehensive, but not exhaustive, list of causes of dyspnea that an anesthesiologist should be familiar with in the emergent and prehospital setting.
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