Air Medical Transport: When Taking Flight with Trauma Patients Makes Sense
Air Medical Transport: When Taking Flight with Trauma Patients Makes Sense
Author: Howard A. Werman, MD, Associate Professor of Clinical Emergency Medicine, The Ohio State University College of Medicine and Public Health, Columbus; Medical Director, MedFlight, Columbus, OH.
Peer Reviewer: Richard J. Hamilton, MD, FAAEM, Associate Professor of Emergency Medicine; Program Director, Emergency Medicine, MCP Hahnemann University, Philadelphia, PA.
Trauma exacts a tremendous toll, claiming more than 150,000 lives each year in the United States. An additional 70 million patients suffer non-fatal injuries. Integrated trauma care systems have become an important component of the U.S. health care system. Trauma care systems are based on the premise that critically injured patients can be identified early and transported to comprehensive trauma resource hospitals for stabilization, definitive care, and ultimately to rehabilitation. Trauma care systems have been shown to improve the outcome of critically injured patients.1-4
An integral part of any trauma care delivery system is air medical response. This includes the use of helicopters, or rotary-wing aircraft, and airplanes, or fixed-wing aircraft. Air transport services are involved in the provision of care directly to the scene of the traumatic event (primary transport) as well as in the movement of patients from smaller community settings to larger trauma resource hospitals (secondary transport).
There are many reasons that air transport services play a pivotal role in the trauma care delivery system. Primary among them is the fact that trauma is a time-critical illness, and air transport offers the important component of speed. Additionally, air transport programs provide the capability of bringing the critical care skills and resources of the trauma resource hospital directly to the bedside or accident scene.
Most emergency physicians encounter air transport services in some fashion. They interact as referring physicians, receiving physicians, or occasionally as consulting physicians for air transport services.
This article describes the special environment of air transport, provides guidelines for the appropriate use of air transport services in trauma care, and discusses some specific issues, including crew configuration, efficacy of air transport, and trauma victim stabilization. Finally, the author describes some developments on the horizon for victims of trauma who are transported by air.—The Editor
The History of Air Transport
The development of air transport services traces its roots to the development of early trauma systems by Jean-Dominique and Percy Larrey, Napoleon’s chief battle surgeons. They conceived a system that provided rapid evacuation of injured soldiers from the battlefront using horse-drawn carts and stabilization of injuries in battlefield hospitals. Once stabilized, the injured soldiers were moved to permanent hospital structures for further treatment and rehabilitation. The concept of trauma systems was refined further by Major Jonathon Letterman during the American Civil War.
Air evacuation is thought to have been accomplished first in 1870 during the Franco-Prussian War when 160 wounded French soldiers were transported by hot-air balloon from the battlefront to army hospitals in France.5
Igor Sikorsky flew the first helicopter mission in 1939. In the United States, the use of this transport mode for patient care was developed during the military conflicts of World War II, the Korean War, and, particularly, during the Vietnam War.6,7 The helicopter became the dominant mode of evacuation from the battlefront to mobile surgical hospitals. Soon, physicians in the civilian sector who had an interest in trauma care began to realize the value of air evacuation in minimizing the prehospital component of the "golden hour."8 Initially, military helicopters were evaluated by their ability to provide medical services to the civilian population as part of the Military Assistance to Safety and Traffic program in the late 1960s. Eventually, dual-purpose public safety and medical helicopter programs began to appear in the United States.9,10
The modern era of air medical transport began in 1972 with the Flight for Life program at St. Anthony’s Hospital in Denver, the first hospital-based air medical transport program established in the United States. By 1990, there were more than 170 air transport programs in operation.11
Physiology of Flight
One of the most important considerations when utilizing an air transport is to understand that there are physiologic consequences of placing the patient in this unique environment. Fortunately, many of the physiologic changes associated with flight are not significant because most rotary aircraft fly at low altitudes, and the cabins of fixed-wing craft are pressurized during transport. The typical altitudes during visual flight rule (VFR) transports are 500-2500 feet above ground. Even instrument flight rule (IFR) transports are undertaken at altitudes at or below 5000 feet above the ground. Propeller-driven fixed-wing aircraft fly at 10,000-15,000 feet above sea level, but with cabin pressurization, the effective altitude is 1000-1500 feet. Non-pressurized aircraft fly at 5000-9000 feet above sea level, and jets fly at 30,000-40,000 feet. Jet transports typically are conducted under a higher cabin altitude than propeller transports.
A major consideration for patients transported by air is the physiologic change in oxygenation that occurs during ascent from ground level to higher altitude. Dalton’s Law states that the total pressure of a mixture of gases is equal to the sum of the partial pressure of each individual gas. As a consequence, when the barometric pressure decreases with ascending altitude, so does the partial pressure of individual gases, including oxygen. The alveolar oxygen concentration is determined by the concentration of inspired oxygen, water vapor pressure, carbon dioxide from expired air, and barometric pressure. As an example, consider that the barometric pressure falls from 760 mmHg to 565 mmHg at 8000 feet. This translates to a decrease in alveolar oxygen pressure from 110 mmHg to 69 mmHg. This reduction in alveolar oxygen has profound effects on oxygen diffusion across the pulmonary capillary membrane, which is determined by the difference between alveolar and capillary oxygen concentration.
The oxygen concentration within the pulmonary capillaries is 40 mmHg. This value is unaffected by altitude. As a result, the driving force for oxygen diffusion across the pulmonary capillary membrane in the example above decreases from 70 mmHg (110 mmHg - 40 mmHg) to 29 mmHg (69 mmHg - 40 mmHg) at an altitude of 8000 feet.
The decrease in arterial oxygen concentration that results from changes in altitude is known as aerohypoxia. In general, symptoms of aerohypoxia rarely are seen at altitudes lower than 5000 feet above sea level. Thus, aerohypoxia is not typically a significant consideration among healthy persons during helicopter transport. There are certain subsets of patients, however, who are very sensitive to even small changes in oxygen concentration related to flight. These include: patients with chronic obstructive pulmonary disease; infants with congenital heart disease; patients with coronary artery disease; victims of shock; patients with sickle cell disease; and neonates with persistent pulmonary shunting during the first 24-48 hours of life. This is a potential problem for transport programs that must operate in mountainous terrain.
Fortunately, the treatment of aerohypoxia is rather straightforward. All critically ill or injured patients transported by air should receive supplemental oxygen. There are methods of determining the exact concentration of inspired air to maintain a paO2 above 80 mmHg. However, during transportation of trauma victims, oxygen concentrations of 100% typically are administered using an appropriate delivery device (usually a non-rebreather mask or endotracheal tube) with careful attention to the oxygen saturation measured by pulse oximetry. When possible, trauma patients who are being transported from a hospital setting should be transported with a serum hemoglobin level of at least 7 g. This assures adequate oxygen-carrying capacity; thus, blood transfusion prior to transport may be required.
Another important consideration is the effect of changes in altitude on the volume of gases. There is an inverse relationship between the volume of a gas and the atmospheric pressure as defined by Boyle’s Law. At 5000 feet, a gas will occupy approximately 20% greater volume than at sea level. (See Table 1.) This has significant implications for aeromedical transport, in which air-filled equipment commonly is used in patient care. Pressures in endotracheal tube cuffs, airway devices such as the Combitube, pneumatic splints, and military antishock trousers (MAST) must carefully be monitored during flight. Air splints, in particular, must be closely observed, as vascular compromise has been reported with changes in altitude of only 1500-2000 feet. Because of entrapped air in glass intravenous bottles, intravenous fluid bags are preferred. When specific medications are being titrated, infusion pumps should be utilized.
|
Table 1. Effects of Altitude |
|
|
Altitude (feet) |
Volume |
|
|
|
| 0 | 1.0 |
| 5000 | 1.2 |
| 10,000 | 1.5 |
| 15,000 | 1.9 |
| 18,000 | 2.0 |
| 20,000 | 2.4 |
|
|
|
When possible, any patient with a suspected or known pneumothorax should have these injuries decompressed prior to flight because of the risk of expansion or development of tension pneumothorax during flight. Additionally, patients with penetrating ocular injuries should be transported at the lowest possible altitude. The retina is highly sensitive to changes in intraocular pressure that may result from expansion of gas within the globe.
Expansion and contraction of gases in enclosed spaces also may cause painful mechanical effects within the body. Common sites of problems include the middle ear, teeth, sinuses, and gastrointestinal tract. During ascent, gas will expand within the body cavity; during descent, the gas will contract. In trauma victims who may be unable to properly equalize body cavity pressures with the atmospheric pressure, pain and mechanical damage can result. Patients with abdominal trauma should have a nasogastric tube placed to avoid any mechanical effects of expanding gases within the gastrointestinal tract.
Gravitational forces and turbulence also may have profound effects on the physiology of the patient. This particularly is true during takeoff and landing of fixed-wing aircraft. Gravitational forces during these critical times can produce a transient redistribution of blood within the body. This is most pronounced in patients who are immobilized in a supine position on cots oriented along the long axis of the aircraft. With the head forward during take-off, for example, blood pools in the lower extremities. This results in a temporary reduction in cardiac output and a concomitant reduction in intracranial pressure. The converse is true during landing. Patient positioning with the head or legs elevated (Trendelenburg position) during take-off can reduce these effects. Obviously, these effects are of greatest concern in patients with marginal cardiovascular reserve or with significant intracranial pathology.
Gravitational forces and turbulence also have significant effects on any unsecured objects, such as weighted traction devices, which can become projectiles during flight. Only tension devices (e.g., Hare splint) should be used to secure injured extremities during air transport. All other supplies and equipment must be carefully secured during air transport to avoid injury to the patient and crew.
Other effects of altitude also must be considered during transport. The temperature decreases 2°C for every 1000 feet of ascent. Typically, the internal temperature of the aircraft is well controlled, but provisions should be made in case of failure. Trauma patients must be kept warm, because their mortality has been shown to be dramatically increased when hypothermia develops.12 Specifically, the use of neuromuscular blocking agents and intubation during air transport predisposes the trauma patient to hypothermia.13
A somewhat related concern is the temperature of medications and supplies stored inside the aircraft. The United States Pharmacopoeia (USP) recommends that drugs be stored between 15°C and 30°C. It has been shown that medications stored in aircraft, like medications stored in ground ambulances, are subject to extreme temperature conditions that exceed temperatures recommended for storage.14-16 The clinical impact of these storage temperatures has not been studied.
Noise inside the aircraft is another important stressor. The typical level of noise in a rotary aircraft has been measured at 90-110 decibels; in comparison, the noise level in an intensive care setting is 58-70 decibels. The most noticeable effect of noise is the inability to perform certain medical assessments routinely during transport, such as lung auscultation or blood pressure measurement.17,18 The esophageal stethoscope has been suggested as an effective alternative for assessment of breath sounds, but this equipment generally is limited to patients who are unconscious and intubated.19,20 In addition, the ability to notice auditory and visual medical equipment alarms may be compromised during air transport.21 Noise also requires that communication during flight between the crew and patient be accomplished through radio headsets.
Vibration of the aircraft may produce pain, discomfort, nausea, vomiting, headache, and muscle fatigue in both crew members and patients. This is of particular concern during long transports.
Motion sickness is a phenomenon associated with all transport modes. Nausea and vomiting are common during air transport, particularly during turbulent conditions. Trauma patients are at particular risk of motion sickness, especially those with elevated intracranial pressure, fluid or electrolyte disturbances, intraocular injury, or abdominal trauma. Promethazine (Phenergan) 12.5-25 mg IVP or other appropriate anti-emetic agents should be administered to patients at high risk of motion sickness.
Indications for Air Transport
It should be remembered that trauma deaths have a tri-modal distribution. Early deaths occur at the accident scene (50%) due to massive head injury or hemorrhage. Another 30% of patients die within hours of injury, and an additional 20% die within days or weeks as the result of sepsis and multiple organ system failure.22 The two latter trauma patient populations may be served effectively by air transport. Of these two groups, the first patient population, at risk of life-threatening hemorrhage within the first few hours following injury, is best identified at the accident scene and directly transported by helicopter to a trauma resource hospital. The direct scene use of the helicopter reduces the time from injury to definitive care and has been shown to reduce the number of preventable trauma deaths.23
The third set of trauma deaths typically is due to sepsis and multiple organ system failure. Air transport to a trauma resource hospital may be appropriate in this group because of the significant resources that may be required during transport and during the subsequent hospital stay.
In making a decision to transport a trauma patient by air, the physician must first consider whether the patient is at risk of life-threatening or potentially life-threatening traumatic injuries. Several triage schemes have been proposed; the National Association of Emergency Medical Service Physicians, the Association of Air Medical Services, and the American College of Surgeons have suggested criteria to identify such patients.24-26
In addition to identifying the severely injured trauma patient, prehospital or hospital personnel must evaluate logistical factors that make air transport a consideration in the care of the trauma patient. These factors can be summarized as speed, smoothness, special skills of the crew, and access. By far the most important consideration is speed; as a general rule, the greater the distance to a trauma resource hospital, the more likely that air transport will be appropriate for transport.
A rough guideline is that helicopters are most appropriate when a trauma facility is 15-100 miles away. Helicopters are utilized best for direct scene response when there is a prolonged period of extrication and, therefore, will be no delay in transfer while awaiting the helicopter. Where distances exceed 100 miles, fixed-wing aircraft typically are considered. Under these circumstances, fixed-wing transports typically are faster and more economical than helicopter transport. However, since there are two additional airport transfers, this must be factored in to the decision to use fixed-wing.
The decision to access the helicopter at the collision site should be made by the most medically experienced person on scene with input from medical control. This input is affected best through well-developed standing orders that can minimize delays in requesting air transport when appropriate. Delays can occur if direct on-line input is sought in cases in which air transport is needed.27 Many emergency medical service (EMS) medical directors retrospectively will review all direct requests for air transport to assure compliance with these written protocols.
The smoothness of transport in an aircraft may provide rationale for choosing a helicopter or airplane. In particular, patients with unstable cervical fractures or profound hypothermia may be excellent candidates for air transfer when ground transport over uneven roads and rough terrain may jeopardize their underlying medical conditions. Scientific validation of the benefit of air transport in this population, however, is lacking.
The special skill of the medical crew also has been cited as a reason for using air medical transport. In many areas of the country, EMS provides a Basic Life Support (BLS) level of care. Helicopters and airplanes allow less-trained EMS services and community hospitals to take advantage of the advanced training of paramedics, critical care nurses, respiratory therapists, and air transport physicians available in tertiary settings. Additional specialized training in neonatal/pediatric management, high-risk obstetrical or burn care is accessible by using transport teams supported by various specialty hospitals.
In certain situations, a combination of these logistical considerations can be used to justify air medical transport in selected clinical situations. A unique example of this debated concept is the use of helicopters to transport potentially salvageable organ donors with isolated intracranial gunshot wounds to trauma centers.28 While there may be support for the transport of such patients who are hemodynamically stable, patients in cardiac arrest with a low survival rate should not be transported by helicopter for purposes of donation.
Finally, helicopter transport has been considered in the appropriate setting where access to the patient has been restricted. Certain terrains, such as mountain clearings or isolated valleys, make the patient potentially inaccessible to ground evacuation. In this setting, air transport may be required. More common than these physical barriers, however, are traffic conditions that restrict access to the patient, making air transport an appropriate choice.
Methods for identifying the appropriate patient for air transport are identical to the methods for identifying the critically injured patient. One set of criteria, based on the American College of Surgeons triage scheme, is listed in Table 2. On scene, physiologic criteria and the location of the injury are important factors to determine. The patient’s mechanism of injury also should be strongly considered. Finally, co-morbidities such as extremes of age or other underlying medical illness are important factors.
| Table 2. Triage Criteria for Transporting Patient to a Trauma Center | |
| Go to Trauma Center: | |
| • | Glasgow Coma Scale score < 13 |
| • | Systolic blood pressure < 90 mmHg |
| • | Respiratory rate < 10 or > 29 |
| • | Revised Trauma Score (T-RTS) < 10 |
| • | Penetrating injury to head, neck, torso, or extremities proximal to elbow or knee |
| • | Flail chest |
| • | Pelvic fractures |
| • | Two or more long bone fractures |
| • | Open or depressed skull fracture |
| • | Paralysis |
| • | Amputation proximal to wrist or ankle |
| Consider Trauma Center: | |
| • | Ejection from automobile or motorcycle |
| • | Death in same passenger compartment |
| • | Fall > 20 feet |
| • | Rollover of vehicle |
| • | High speed crash (speed > 40 mph; major deformity > 20 inches; intrusion into passenger compartment by > 12 inches) |
| • | Auto/pedestrian or auto/bicycle collision with significant impact |
| • | Pedestrian thrown or run over |
| • | Motorcycle crash > 20 mph or separation of rider from bike |
| • | Age < 5 or > 55 |
| • | Cardiac or respiratory disease |
| • | Insulin-dependent diabetes, cirrhosis, or morbid obesity |
| • | Pregnancy |
| • | Immunocompromised state |
| • | Patient on anticoagulants or with a bleeding disorder |
|
|
|
| (Used with permission from: Committee on Trauma—American College of Surgeons. Resources for Optimal Care of the Injured Patient: 1999.) | |
|
|
|
While excellent reviews of trauma triage tools exist, there are major problems with the use of any one set of criteria.29 An ideal trauma triage tool allows the provider to transport the severely injured trauma patients to centers with committed resources and personnel, while preventing utilization of these resources in less severely injured patients who can remain in their community health care facility. In short, these tools should have a low overtriage and low under-triage rate.
In air transport, over-triage implies that a less severely injured patient is taken to a trauma resource hospital from the trauma scene, or air transport is utilized to move a patient from a non-trauma resource hospital to a trauma center when such resources are not needed. Reducing over-triage is imperative if the triage tool is to address the political and economic ramifications of a trauma system for community hospitals. It also should be remembered that care in a trauma setting is resource intensive; appropriate treatment of patients in their own communities results in an overall cost-efficient care system and does not overwhelm the resources of the trauma resource hospital and EMS system.
Equally important is under-triage, which implies that a patient who potentially could have benefited from direct transfer to a trauma center instead was taken to a non-trauma facility. In those patients who have time-critical traumatic injuries, this may result in unnecessary delays in appropriate care, with increased mortality and morbidity.23
Physiologic scoring systems include the Revised Trauma Score (T-RTS), CRAMS (circulation, respiration, abdomen, motor reponse, speech) score, or Prehospital Index (PHI).30-32 These scoring systems are based on easily measured physiologic variables (blood pressure, pulse rate, respiratory rate, etc.) that are available on-scene and reliably can be measured by providers with varying levels of training. These measures alone lack sensitivity and fail to identify critical patients who possess significant injuries but who are physiologically compensated at the initial presentation. With the addition of anatomic criteria and the mechanism of injury, the under-triage rate can be reduced. Unfortunately, this typically is done at the expense of increasing the over-triage rate. In one county EMS system, the addition of the mechanism of injury and anatomic criteria to a physiologic triage score resulted in the appropriate triage of 95% of patients to trauma centers (under-triage of only 5%), while increasing the number of over-triaged patients to 28%.33 A similar study examining helicopter on-scene triage found that physiologic criteria alone resulted in an undertriage rate of 44.4%.34 However, the addition of anatomic criteria and mechanism of injury decreased the under-triage rate to 2.6% but increased over-triage to 92%. Other studies have shown a far less dramatic increase in over-triage.35
One additional point must be made. There is credible evidence that the judgment of the EMTs on-scene may better identify patients appropriate for a trauma center than any of the triage rules described above. In one study, it was shown that on-scene personnel were better at predicting the need for early operative intervention than either the CRAMS or T-RTS rules.36 This was confirmed in a more recent study, which showed that the Trauma Triage Rule had a sensitivity of 88% and specificity of 86%, compared to the judgment of the on-scene providers, who predicted the need for a trauma center with a sensitivity of 98% and specificity of 60%.37
In addition to difficulties in balancing over-triage and under-triage rates using various triage criteria, proper identification of a severely injured patient using these scores is limited by other problems as well.38,39 These include failure of triage schemes to address specific subsets of trauma patients (i.e., penetrating trauma; elderly, pediatrics); the low overall prevalence of major trauma; poor inter-rater reliability; the dynamic nature of the trauma patients; and limitations in prehospital data completeness.
Perhaps the most difficult issue in assessing the true over-triage and under-triage rates for triage tools has been finding a consistent end-point that accurately reflects which patients require treatment at a trauma center. In defining an appropriate end-point, remember the two distinct populations: those patients who require immediate evaluation and treatment for potentially life-threatening injuries; and those who initially are evaluated and stabilized outside of a trauma center but whose injuries require either expertise or resources unavailable in the community setting. Difficulty has arisen in the literature not only in identifying the patient who is best managed in a trauma center, but also in sorting these two distinct groups of trauma patients. Various studies have proposed outcomes such as injury severity scores (ISS) greater than 15, trauma mortality, need for immediate non-orthopedic surgery, intensive care admission, requirement for blood transfusion to maintain systolic blood pressure, invasive central nervous system monitoring, and a combination of these factors as appropriate end-points in defining the trauma patient. It seems logical to propose that when specifically considering the benefit of direct air transfer from the scene, for example, studies that include end-points such as a high likelihood for mortality or an immediate need for non-orthopedic surgery would provide the most appropriate outcomes for analysis.
The decision to transfer patients who initially are evaluated in non-trauma facilities is less clear cut, and triage instruments for this population are not well-defined. As previously stated, the decision may be based on the need for specific specialty services or medical resources that exceed the capabilities of the local facility. Most commonly, it is the patient in need of a time-sensitive procedure (i.e., surgery, angiography, hyperbaric oxygen therapy, etc.) or a patient whose clinical condition is unstable based on the judgment of the referring physician who will most benefit from air medical transport.
Just as there are definite indications for air transfer of patients, there are clear contraindications for use of helicopters and fixed-wing aircraft for patient transports. Obviously, the patient who has stable traumatic injuries and who is not determined to be at high risk for life-threatening problems during transfer should be transported by ground ambulance. This clearly is the most cost-effective method of transfer and allows greater availability of limited resources. The Commission on Air Medical Transport Systems requires each program to have a utilization review program in place to evaluate the appropriate use of its air transport resources.40
Weather is another limiting consideration in determining the ability to transfer a patient by air transport. Each program is bound by specific weather minimums that must be met before the aircraft safely can fly. The pilot’s assessment of the prevailing weather conditions prior to flight must be completely objective and made in the absence of any clinical information, thus removing any emotional factors from the decision-making process.41
One additional contraindication that should be addressed relates specifically to trauma victims. Patients with blunt trauma who are found to be in cardiac arrest and those with penetrating trauma who have no vital signs for more than 10 minutes are not viable. The use of helicopter resources for these patients is not believed to convey any additional benefit.42-44 It should be noted, however, that those patients who are resuscitated after sustaining a traumatic cardiac arrest may benefit from transport. One study showed a 19% survival rate among survivors of traumatic cardiac arrest who subsequently were transported by air to a trauma resource hospital.45
Patient Stabilization for Transport
The basic principles of patient stabilization, as prescribed by the Advanced Trauma Life Support course, Prehospital Trauma Life Support course, and Basic Trauma Life Support course, apply to trauma patients who are transported by air as well as by ground. Scene responders should immobilize the patient on a long backboard in a neutral position. Hospital transfers generally are packaged in a similar manner, although the decision to immobilize should be based on the patient’s mechanism of injury, presence of spine tenderness, neurologic examination, and presence of other distracting injuries. Copies of the patient’s medical records—including emergency department chart, critical care flow sheets, laboratory studies, and radiographs—should accompany the patient for inter-hospital transfers. A clear record of any medications administered, particularly antibiotics and tetanus toxoid, should be present. With regard to specific radiographs, a single AP radiograph of the chest is the minimum study that should be obtained prior to transport. Radiographs of the cervical spine and pelvis, while helpful, are not absolutely necessary if the patient remains properly immobilized during transport. Other, more controversial issues surrounding patient stabilization are described below.
Airway Management. Attention to the airway is paramount prior to air transport. Early intubation has been shown to positively impact survival of trauma patients.46,47 The special airway skills possessed by air medical crews are required in a significant percentage of transports.48 When possible, a patent airway should be aggressively secured prior to air transport; however, this should not significantly prolong the time at the scene or delay transfer from the hospital. Remember that endotracheal intubation can be performed in any aircraft, although limited space, poor lighting, noise, and vibration create technical difficulties in performing the procedure. Studies have shown that the number of intubation attempts is higher and the success rate is lower when in-flight intubation is compared to pre-flight intubation.49,50 These difficulties may explain why air medical crews tend to be more aggressive than hospital and scene personnel in establishing a definitive airway prior to transport. On the other hand, it should be noted that the success rate in each of these settings was demonstrated to be higher than 95%, whether the airway attempt was made in the aircraft or in a pre-transport environment.51
The optimal method of securing the airway in a trauma patient has been the subject of much recent debate. Orotracheal intubation using a rapid sequence induction technique has gained prominence in the recent literature. This method particularly is helpful in treating trauma patients, who often are alert enough to resist the procedure but still need to minimize movement of the cervical spine. A rapid sequence induction should be undertaken with great caution. The patient loses the ability to breathe spontaneously and protect his airway as a consequence of the procedure. Hence, use of a rapid sequence induction technique should be limited to those medical personnel who can be trained appropriately and closely supervised in performing this procedure.
Flight crews generally consist of a finite number of highly trained, well-supervised individuals who, by virtue of the range of the helicopter or airplane, can provide this important service to a broad region. Clinical studies have demonstrated the excellent success in flight programs that have implemented a rapid sequence induction protocol.52-55 The complication rate for this procedure in the flight environment is low, with multiple attempts at intubation representing the most frequent complication.56 The procedure can be performed with equal precision prior to or during transport of the patient.57 However, it should be pointed out that when performed in the prehospital setting, prolonged ground times have been documented.58
Other airway methods also have been used in the air transport environment. Lighted stylet intubation and digital intubation techniques have received very little attention in the air medical transport literature.59 Surgical cricothyrotomy has been used in a small percentage of missions. Flight nurses trained in this procedure can be taught to perform it competently with success and complication rates comparable to reported reviews of physicians trained in this skill.60 This procedure typically is used as an airway of last resort in patients who have failed oral and nasal intubation attempts with limited patient salvage of less than 50%.61,62 It also may be a primary airway in patients with massive face or neck injuries.63 The complication rate with this procedure in the prehospital environment has been reported to be as high as 31%.64
Recently, the laryngeal mask airway has been advocated in cases where tracheal intubation is not technically feasible.65 This alternative airway offers the advantage of being easy to insert, causing little tissue damage, and having few post-insertion complications. In addition, it does not require manipulation of the neck during insertion, thus providing protection to the cervical spine. The esophageal tracheal Combitube also has been shown to be effective in the air transport setting when intubation with a rapid sequence induction technique has failed.66
Because of concerns about aerohypoxia, all trauma patients transferred by air should receive supplemental oxygen for transport, especially those patients with suspected hemorrhage, shock, or respiratory difficulties. Remember that these problems will be compounded by transport at high altitude.
Chest Injuries. Patients with known or suspected pneumothoraces should have these injuries decompressed prior to flight. Remember that these injuries will expand with ascent during transport. However, many patients transported directly from the accident scene arrive in stable clinical condition with pneumothoraces identified on chest radiograph during initial evaluation. In one study alone, 16.5% of all scene trauma patients transported from an accident scene were found to have either a pneumothorax or hemothorax that was evacuated upon arrival to the trauma center without apparent clinical compromise during transport.67
Circulation. Secure intravenous access should be obtained in all trauma patients being transported by helicopter or airplane. In this way, fluid resuscitation, blood products, and appropriate medications can be administered during transport. There is a significant body of recent experimental and clinical data suggesting the trauma patients might benefit from some degree of fluid restriction.68-70 However, the single clinical trial that examined this issue was conducted in an urban environment with penetrating torso injuries and short transport times.71 The clinical application of these findings to the air transport environment—with patients, primarily with blunt injuries, who typically are transported over greater distances from suburban and rural environments—is not clear.
The use of MAST, or pneumatic antishock garment, in air-transported trauma patients is equally controversial. MAST may be useful in stabilizing pelvic and long-bone lower extremity fractures. The use of the device for intra-abdominal injuries is of questionable value, particularly in patients with penetrating injuries.72-74 A recent study in an urban setting also was unable to find any benefit to application of MAST.75 Here again, data specifically evaluating use of the device in those patients transported by air services have not been addressed. While compartment syndrome has been reported in patients who have had MAST in place, it is unknown whether air transport increases this risk due to expansion of the air-filled compartments.
Efficacy of Air Transport
The most basic question that must be addressed is the efficacy of air transport in the trauma patient. Surprisingly, there clearly is very limited data from which to draw conclusions. The most common method of studying this issue has been through the use of TRISS (trauma score and injury severity score) methodology, in which a group of trauma patients is characterized by their average trauma scores (RTS), ISS, age, and injury type (blunt or penetrating).76 Based on this information, a statistical analysis is conducted in which the predicted death rate for two groups of patients is determined, typically one transported by air and a clinically equivalent group transported by ground. The predicted and actual mortality between both groups then is compared, and any difference between the study groups is attributed to the mode of transport.
Using TRISS methodology, one study compared 150 patients transported by either ground or air to a Level I trauma center.77 While the ground transport group showed a slight increase in the number of predicted deaths, the air transport group demonstrated nearly a 50% reduction in the number of predicted deaths. The authors suggested that the benefit was due to both the speed of transport as well as the critical care skills provided by a highly trained crew. A follow-up study evaluating seven air transport programs showed an improvement in mortality from 4-40% among these transport programs using the same methodology.78 Finally, a more recent review of a statewide trauma registry showed that when categorized by initial trauma score, the survival rate was significantly higher among patients transported by air vs. ground.79 Similar methodology used in the pediatric population also has demonstrated an improved survival rate of 1.1 unexpected survivals for each 1000 patients transported in patients transported by helicopter.80 Two early studies also supported the benefit of air transport in improving the outcome of trauma patients in a rural environment using a more subjective method of assessing benefit.81,82
Other studies have not been able to demonstrate a significant impact on overall mortality for trauma transports from the scene of injury.83 However, when the subset of patients with an ISS between 16 and 60 was considered, the regression analysis in this study showed the mode of transport had significant impact on outcome. This is not surprising, since patients with an ISS less than 16 are not severely injured and would not be expected to benefit from rapid transport. Similarly, patients with an ISS greater than 60 are so severely injured that there is little that can be done to improve their outcome. Others also have emphasized that air transport has proven benefit in only a subset of injured patients.84
Still other studies have not been able to demonstrate a benefit to air transport in subsets of trauma patients. One group suggested a 16% increase from predicted deaths among patients transported by helicopter, vs. only a 2% increase with ground transport.85 This study specifically has been attacked for the conclusions drawn by its authors.86,87
In truth, each of these cited studies can be criticized for flawed methodology. It must be conceded that the design of a truly randomized, double-blinded, controlled clinical trial evaluating the benefit of air transport would be difficult to develop.
If one accepts the premise that air transport does decrease mortality in trauma patients, as established by these studies, it is interesting to examine whether air transport is cost-effective. This is more than just a trivial concern. In 1991, the estimated costs of air medical transport programs exceeded $250 million.88 This matter specifically was considered by one group, who conducted a cost/benefit analysis using the data cited above.89 Using the most conservative figures, these authors found a discounted cost per year of life saved of $9677. Interestingly, this compares favorably with the costs of other commonly accepted life-saving medical interventions, such as implementation of an ALS system ($8886/year of life saved), use of thrombolytic agents ($32,678/year of life saved), and administration of prophylactic AZT for needlestick exposure ($41,000/year of life saved). Other studies also have confirmed that the use of helicopters is cost-effective when compared to ground ambulances with similar crew configuration to achieve the same level of rapid response for trauma.90,91
The exact nature of benefit conveyed by helicopter transport is not certain. The clinical benefit may be due either to the speed of the transport mode or the clinical skills of the crew. The impact of speed itself has not been well studied, although there is clear evidence that air transport does not have a similar benefit in the transport of trauma patients in the urban environment.92,93 One group supported a limited role for helicopters in urban areas and suggested that air transport in the urban environment should be limited to, "1) critically wounded patients likely to require care beyond the capabilities of the first-responder EMS personnel, or 2) when arrival at an appropriate trauma center will be substantially hastened by helicopter transport." In reality, such situations are rare in the urban setting.94
On the other hand, the benefit of the critical skills of the air medical crew is unknown. The efficacy of Advanced Life Support (ALS) care, however, has been hotly debated in the trauma literature. Several authors have suggested that critical skills, such as establishing a definitive airway or intravenous access, improve the status of trauma patients prior to arrival at the trauma center.95,96 When an aggressive resuscitation protocol was used by an air medical service in patients with severe closed head injury, there was an 11% decrease in mortality and 10% improvement in discharge status.97 However, other authors have argued that advanced life support measures only delay transport to a definitive care facility and do not contribute to a better outcome.98,99 A recent meta-analysis reviewing this literature seems to support this notion.100 While this question remains unanswered, it is likely that over the longer distances which trauma patients are typically transported by air that both the skills of the medical crew and speed of have an impact on outcome.101
The benefit of air transport in inter-hospital transfer of trauma patients also has been examined. In comparing ground vs. air transfer of such patients using TRISS methodology, one group demonstrated a 25% reduction in predicted mortality in the air transport group.102 It should be noted that this occurred despite a statistically significant difference in ISS between the groups (34.9 [air] vs. 25.5 [ground]). These conclusions support other work in this area.103
Crew Configuration
Ideally, the crew configuration for each transport would be tailored to meet the needs of the individual patient. However, practical considerations, such as rapid mobilization and training costs, preclude this amount of flexibility, particularly among rotary-wing transport programs. There is, however, greater flexibility with fixed-wing transports, which tend to involve more stable trauma patients who have fewer time constraints.
To date, there have been no prospective, randomized, double-blinded trials examining the issue of optimal crew configuration, and it is difficult to imagine how such a trial might conceivably be designed. The few studies that have been conducted have evaluated the subjective impression of medical crew members on the benefits of physician presence or have examined the use of specific procedures and medications thought to lie within the scope of practice of a physician. Fewer studies have directly compared the performance of nurse/physician teams to other configurations or have evaluated outcomes of patients transported by differing medical crews.
One group conducted a retrospective review of 395 patient transports where a physician/nurse team was utilized.104 Each transport was evaluated as to whether a physician was necessary, potentially necessary, or was not needed, based on rigid criteria reflecting physician judgment and skill. Judgment included a change in diagnosis, establishment of a new diagnosis, treatment alteration, or adjustment of a critical medication. Interventions included airway control, pericardiocentesis, tube thoracostomy, and central venous cannulation. Patients who may have required a physician included those receiving critical care medications and those in active labor. The authors found that the physician was necessary in 25.6% of cases, potentially necessary in 34.7%, and not necessary in 39.7% of cases, according to these criteria. In the 101 patients felt to require a physician, judgment was needed in 55 cases, 16 required the physician’s skills and 31 required both physician’s judgment and skills. The authors concluded that a physician was an essential part of the air transport team.
One study examined the contribution of a physician presence on the helicopter shortly after the implementation of their flight program at the University of Michigan.105 The authors specifically considered two areas of physician contribution: technical skills and clinical judgment. The physician’s clinical contribution was assessed by a survey of transport nurses. The study suggested that the physician had an overall impact in 22% of transports. In 17% of cases, the physician’s judgment alone was felt to be beneficial; in 4% both the judgment and technical skills were helpful; and in only 1% did technical skills contribute to the patient’s outcome. The authors suggested, however, that in comparing the results of their investigation to other transport programs, one needs to consider the patient mix, level of training and experience of flight nurses, training level of transport physicians, and the indirect medical consequences of physician presence as part of the transport team.
Another study noted that in rural areas where transport times are long, flight physicians were called upon to perform invasive procedures in 45% of trauma patients.106 The authors concluded that the ability of flight physicians to perform invasive procedures provided some benefit during these transports.
On the other hand, one group surveyed flight personnel when their transport program changed from a physician-staffed service to a nurse/nurse crew.107 The nurses found that the need for physician judgment decreased from 21% to 1% of cases and technical skills of the physician were required in only 3% of cases (decreased from 11%). This was clearly a purely subjective paper. The study demonstrated that once physicians were not part of the flight team, nurses were far less reliant on their input and skills.
In evaluating trauma patients, another study compared the predicted mortality for patients transported by nurse/paramedic crews vs. nurse/physician crews.108 They were able to make comparisons within their air transport program, which operated two helicopters with these distinct crew configurations. The authors utilized TRISS methodology, in which the observed mortality rates were compared to the predicted mortality rates among similar patients who are part of a large, multi-center trauma database. The authors found that the predicted mortality for the nurse/physician group was 11 patients, whereas the actual mortality was 16.9. In the nurse/paramedic group, predicted mortality was 19 and actual mortality was 19.5. The authors noted a 35% reduction in mortality in the nurse/physician group, which was statistically better than that of the nurse/paramedic group. They postulated that this might be due to more aggressive treatment in the nurse/physician team’s patients. However, they cautioned that "the question of placing a physician aboard a helicopter in which only one of every 50 patients treated would be affected must be given critical consideration." Additionally, one group directly challenged the conclusions of this study, criticizing the authors for drawing statistical conclusions based on a population with few actual mortalities.109 Another group used similar methods in its study comparing 145 adult trauma patients transported by a nurse/physician team to 114 patients transported by nurse/nurse or nurse/paramedic team.110 The authors found an actual mortality of 12 patients, with a predicted mortality of 17 patients in the physician-staffed group (a 29% reduction). By comparison, the non-physician teams had an actual mortality of 8 patients, although the predicted mortality was 15 (a 47% reduction). Finally, another study compared the outcomes of patients transported over a two-year period by a physician/nurse team vs. a nurse/nurse team.111 These authors could find no difference in outcome with more than 1170 patients transported.
Clearly, the literature does not present a clear picture regarding the role of the physician on the transport team. In his review of this topic, one group concluded that "well-trained health care providers, whether they be nurses, paramedics or physicians, can be effective crew members."112
It is interesting to note that the industry has been moving away from physician-staffed crews during the last few years. When surveyed in 1988, the air ambulance industry had nurse/physician crews in 10% of the programs surveyed. The most common combination at that time was nurse/paramedic (44%), followed by nurse/nurse crew (15%). Seventeen percent of programs surveyed flew a nurse along with another health care professional. In the most recent survey, nurse/physician teams are found in only 5% of programs surveyed.113 Two-thirds of the programs surveyed have a nurse/paramedic team. Other configurations included nurse/nurse (8%) and nurse/other (7%). There is no doubt that economic factors have played a significant part in this historical trend.
Future Directions
Clearly, there are many questions regarding the use of air medical transport yet to be addressed. Additional sound research must validate the notion that air medical transport contributes to an improved patient outcome and is cost-effective. The optimal crew configuration for trauma transports must be examined by further investigation. While developing treatment strategies are emerging in the early care of the trauma patient, each modality must be examined from the perspective of the air transport environment. New paradigms in fluid resuscitation, developments in blood substitutes, airway management, and the use of pneumatic trousers are emerging in trauma care. In considering any of these developments, the unique environment of air transport must be considered.
One area clearly on the horizon is the use of ultrasonography in the evaluation of the trauma patient during air transport. One group was the first to demonstrate that this modality could be used to evaluate the abdomen during air transports.114,115 Another study further showed that it was possible to train air transport nurses in the use of this device.116 And another group has demonstrated that the images obtained are equivalent in quality to those obtained during stationary ultrasonography.117 The impact of this emerging technology on patient outcome has yet to be explored.
References
1. West JG, Trunkey DD, Lim RC. Systems of trauma care. A study of two countries. Arch Surg 1979;114:455-460.
2. West JG, Cales RH, Gazzaniga AB. Impact of regionalization. The Orange County experience. Arch Surg 1983;118:740-744.
3. Shackford SR, Mackersie RC, Hoyt DB, et al. Impact of a trauma system on outcome of severely injured patients. Arch Surg 1987;122:523-527.
4. Kane G, Wheeler NC, Cook S, et al. Impact of the Los Angeles County Trauma System on the survival of seriously injured patients. J Trauma 1992; 32:576-583.
5. Green RL. The carriage of invalid passengers by air. Br J Hosp Med 1977; 17:32.
6. Neel S. Helicopter evacuation in Korea. US Armed Forces Med J 1955;6: 691-702.
7. Neel S. Army aeromedical evacuation procedures in Vietnam: Implications for rural America. JAMA 1968;204:309-313.
8. Schwab CW, Peclet M, Zackowski SW, et al. The impact of an air ambulance system on an established trauma center. J Trauma 1985;25:580-586.
9. Myers RN, Angelides AP, Haupt GJ. A civilian aeromedical lifesaving plan HELP. Pa Med 1965;68:51-53.
10. Cowley RA, Hudson F, Scanlan E, et al. An economical and proved helicopter program for transporting the emergency critically ill and injured patient in Maryland. J Trauma 1973;13:1029-1038.
11. No authors listed. Directory of Air Medical Services. J Air Med Transport 1992;11:23-37.
12. Jurkovich GJ, Greiser WB, Luterman A, et al. Hypothermia in trauma victims: An ominous predictor of survival. J Trauma 1987;27:1019-1024.
13. Semonin-Holleran R, Davis K, Storer D. Neuromuscular blockade and intubation: Association with hypothermia in the air medical trauma patient. Air Med J 1994;13:483-485.
14. Valenzuela TD, Criss EA, Hammargren WM, et al. Thermal stability of prehospital medications. Ann Emerg Med 1989;18:173-176.
15. Johansen RB, Schafer NC, Brown PI. Effect of extreme temperatures on drugs for prehospital ACLS. Am J Emerg Med 1993;11:450-452.
16. Madden JF, O’Connor RE, Evans J. The range of medication storage temperatures in aeromedical emergency medical services. Prehosp Emerg Care 1999;3:27-30.
17. Hunt RC, Bryan DM, Brinkley VS, et al. Inability to assess breath sounds during air medical transport by helicopter. JAMA 1991;265:1982-1984.
18. Poulton TJ, Worthington DW, Pasic TR. Physiologic chest sounds and helicopter engine noise. Aviat Space Environ Med 1994;65:338-340.
19. Bugnitz M, Mantz D. Use of the esophageal stethoscope in pediatric transports. Air Med J 1993;12:429-430.
20. Stone CK, Stimson A, Thomas SH, et al. The effectiveness of esophageal stethoscopy in a simulated in-flight setting. Air Med J 1995;14:219-221.
21. Fromm RE Jr., Campbell E, Schlieter P. Inadequacy of visual alarms in helicopter air medical transport. Aviat Space Env Med 1995;66:784-786.
22. Trunkey D. Initial treatment of patients with extensive trauma. N Engl J Med 1991;324:1259-1263.
23. Falcone RE, Herron H, Werman H, et al. Air medical transport of the injured patient: Scene versus referring hospital. Air Med J 1998;17:161-165.
24. No authors listed. National Association of Emergency Medical Services Physicians. Air medical dispatch: Guidelines for scene response. Prehospital Disaster Med 1992;7:75-78.
25. No authors listed. Association of Air Medical Services. Position on the appropriate use of emergency air medical services. J Air Med Transp 1990;9:29-30.
26. No authors listed. Committee on Trauma, American College of Surgeons. Prehospital trauma care resources for optimal care of the injured patient. Bull Am Coll Surg 1999:13-18.
27. Tortella BJ, Lavery RF, Kamat M, et al. Requiring on-line medical command for helicopter request prolongs computer-modeled transport time to the nearest trauma center. Prehospital Disaster Med 1996;11:261-264.
28. Cocanour CS, Ursic C, Fischer RP. Does the potential for organ donation justify scene flights for gunshot wounds to the head? J Trauma 1995;39:968-970.
29. Rodenberg H. Scoring systems in air medical transport: A primer. Air Med J 1996;15:184-190.
30. Champion HR, Sacco WJ, Copes WS, et al. A revision of the Trauma Score. J Trauma 1989;29:623-629.
31. Gormican SP. CRAMS scale: Field triage of trauma victims. Ann Emerg Med 1982;11:132-135.
32. Koehler JJ, Malafa SA, Hillesland J, et al. A multicenter validation of the prehospital index. Ann Emerg Med 1987;16:380-385.
33. Henry MC, Hollander JE, Alicandro JM, et al. Incremental benefit of individual American College of Surgeons trauma triage criteria. Acad Emerg Med 1996;3:992-1000.
34. Bond RJ, Kortbeek JB, Preshaw RM. Field trauma triage: Combining mechanism of injury with the prehospital index for an improved trauma triage tool. J Trauma 1997;43:283-287.
35. Wuerz R, Taylor J, Smith JS. Accuracy of trauma triage in patients transported by helicopter. Air Med J 1996;15:168-170.
36. Ornato J, Mlinek EJ, Craren EJ, et al. Ineffectiveness of the trauma score and the CRAMS scale for accurately triaging patients to trauma centers. Ann Emerg Med 1985;14:1061-1064.
37. Fries GR, McCalla G, Levitt MA, et al. A prospective comparison of paramedic judgment and the trauma triage rule in the prehospital setting. Ann Emerg Med 1994;24:885-889.
38. Plant JR, MacLeod DB, Korbeek J. Limitations of the prehospital index in identifying patients in need of a major trauma center. Ann Emerg Med 1995; 26:133-137.
39. Baxt W, Berry C, Epperson MD, et al. The failure of prehospital trauma prediction rules to classify trauma patients accurately. Ann Emerg Med 1989;18:1-8.
40. Commission on Accreditation of Medical Transport Systems. Accreditation Standards of the Commission on Accreditation of Medical Transport Systems (4th Edition). October, 1999.
41. Steinbrunn RN. Preventing and controlling inadvertent IFR (instrument flight rule encounters). Air Med J 1993;12:315-318.
42. Wright SW, Dronen SC, Combs TJ, et al. Aeromedical transport of patients with post-traumatic cardiac arrest. Ann Emerg Med 1989;18:721-726.
43. Boyd M, Vanek VW, Bourguet CC. Emergency room resuscitative thoracotomy: When is it indicated? J Trauma 1992;33:714-721.
44. Falcone RE, Herron H, Johnson R, et al. Air medical transport for the trauma patient requiring cardiopulmonary resuscitation: A 10-year experience. Air Med J 1995;14:197-205.
45. Margolin DA, Johann DJ Jr, Fallon WF Jr, et al. Response after out-of-hospital cardiac arrest in the trauma patient should determine aeromedical transport to a trauma center. J Trauma 1996;41:721-725.
46. Winchell RJ, Hoyt DB. Endotracheal intubation in the field improves survival in patients with severe head injury. Trauma Research and Education Foundation of San Diego. Arch Surg 1997;132:592-597.
47. Frankel H, Rozycki G, Champion H, et al. The use of TRISS methodology to validate prehospital intubation by urban EMS providers. Am J Emerg Med 1997;15:630-632.
48. O’Malley RJ, Rhee RJ. Contribution of air medical personnel to the airway management of injured patients. Air Med J 1993;12:425-428.
49. Mishark KJ, Vukov LF, Gudgell SF. Airway management and air medical transport. J Air Med Trans 1992;11:7-9.
50. Harrison T, Thomas SH, Wedel SK. In-flight oral endotracheal intubation. Am J Emerg Med 1997;15:558-561.
51. Thomas SH, Harrison T, Wedel SK. Flight crew airway management in four settings: A six-year review. Prehosp Emerg Care 1999;3:310-315.
52. Syverud SA, Borron SW, Storer DL, et al. Prehospital use of neuromuscular blocking agents in a helicopter ambulance program. Ann Emerg Med 1988; 17:236-242.
53. Murphy-Macabobby M, Marshall W, Schneider C, et al. Neuromuscular blockade in aeromedical airway management. Ann Emerg Med 1992;21: 664-648.
54. Rose WD, Anderson LD, Edmond SA. Analysis of intubations. Before and after establishment of a rapid sequence intubation protocol for air medical use. Air Med J 1994;13:475-478.
55. Lowe L, Sagehorn K, Madsen R. The effect of a rapid sequence inducation protocol on intubation success rate in an air medical program. Air Med J 1998;17:101-104.
56. Sing RF, Rotondo MF, Zonies DH, et al. Rapid sequence induction for intubation by an aeromedical transport team: a critical analysis. Am J Emerg Med 1998;16:598-602.
57. Slater EA, Weiss SJ, Ernst AA, et al. Preflight versus en route success and complications of rapid sequence intubation in an air medical service. J Trauma 1998;45:588-592.
58. Falcone RE, Herron H, Dean B, et al. Emergency scene endotracheal intubation before and after the introduction of a rapid sequence induction protocol. Air Med J 1996;15:163-166.
59. Kociszewski C, Thomas SH, Wedel SK. Evaluation of three oral intubation techniques in the AS365N2 Dauphin. Air Med J 1998;17:16-19.
60. Nugent WL, Rhee KJ, Wisner DH. Can nurses perform surgical cricothyrotomy with acceptable success and complication rates? Ann Emerg Med 1991;20:367-370.
61. Miklus RM, Elliott C, Snow N. Surgical cricothyrotomy in the field: Experience of a helicopter transport team. J Trauma 1989;29:506-508.
62. Xeropotamos NS, Coats TJ, Wilson AW. Prehospital surgical airway management: 1 year’s helicopter experience from the Helicopter Emergency Medical Service. Injury 1993;24:222-224.
63. Gerich TG, Schmidt U, Hubrich V, et al. Prehospital airway management in the acutely injured patient: The role of surgical cricothyrotomy revisited. J Trauma 1998;45:312-314.
64. Spaite DW, Joseph M. Prehospital cricothyroidotomy: An investigation of indications, technique, complications, and patient outcome. Ann Emerg Med 1990;19:279-285.
65. Martin SE, Ochsner G, Jarman RH, et al. Use of the laryngeal mask airway in the air transport when intubation fails. J Trauma 1999;47:352-357.
66. Blostein PA, Koestner AJ, Hoak SH. Failed rapid sequence induction in trauma patients: Esophageal tracheal combitube is a useful adjunct. J Trauma 1998;44:534-537.
67. Cameron PA, Flett K, Kaan E, et al. Helicopter retrieval of primary trauma patients by a paramedic helicopter service. Aust N Z J Surg 1993;63: 790-797.
68. Bickell WH, Bruttig SP, Millnamow MA, et al. The detrimental effects of intravenous crystalloid after aortotomy in swine. Surgery 1991;110:529-536.
69. Stern SA, Dronen SC, Birrer P, et al. Effect of blood pressure on hemorrhage volume and survival in a near-fatal hemorrhage model incorporating a vascular injury. Ann Emerg Med 1993;22:155-163.
70. Matsuoka T, Hildreth J, Wisner DH. Uncontrolled hemorrhage from parenchymal injury: Is resuscitation helpful? J Trauma 1996;40:915-921.
71. Bickell WH, Wall MJ Jr, Pepe PE, et al. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. N Engl J Med 1994;331:1105-1109.
72. Bickell WH, Pepe PE, Bailey ML, et al. Randomized trial of pneumatic antishock garment in the prehospital management of penetrating abdominal injuries. Ann Emerg Med 1987;16:653-658.
73. Honigman B, Lowenstein SR, Moore EE, et al. The role of pneumatic antishock garment in penetrating cardiac wounds. JAMA 1991;266:2398-2401.
74. Schneider PA, Mitchell JM, Allison EJ Jr. The use of military antishock trousers in trauma: A reevaluation. J Emerg Med 1989;7:497-500.
75. Chang FC, Harrison PB, Beech RR, et al. PASG: Does it help in the management of traumatic shock? J Trauma 1995;39:453-456.
76. Boyd CR, Tolson MA, Copes WS. Evaluating trauma care: The TRISS method. The Trauma Score and Injury Severity Score. J Trauma 1987;27: 370-378.
77. Baxt WG, Moody P. The impact of a rotorcraft aeromedical emergency care service on trauma mortality. JAMA 1983;249:3047-3051.
78. Baxt WG, Moody P, Cleveland HC, et al. Hospital-based rotorcraft aeromedical emergency care services and trauma mortality: A multicenter study. Ann Emerg Med 1985;14:859-864.
79. Cunningham P, Rutledge R, Baker CC, et al. A comparison of the Association of helicopter and ground ambulance transport with the outcome of injury in trauma patients transported from the scene. J Trauma 1997;43:940-946.
80. Moront ML, Gotschall CS, Eichelberger MR. Helicopter transport of injured children: System effectiveness and triage criteria. J Pediatr Surg 1996;31: 1183-1186.
81. Urdaneta LF, Sandberg MK, Cram AE, et al. Evaluation of an emergency air transport service as a component of a rural EMS system. Am Surg 1984;50: 183-188.
82. Urdaneta LF, Miller BK, Ringenberg BJ, et al. Role of an emergency helicopter transport service in rural trauma. Arch Surg 1987;122:992.
83. Brathwaite CEM, Rosko M, McDowell R, et al. A critical analysis of on-scene helicopter transport on survival in a statewide trauma system. J Trauma 1998;45:140-146.
84. Cunnigham P, Rutledge R, Baker CC, et al. A comparison of the association of helicopter and ground ambulance transport with the outcome of injury in trauma patients transported from the scene. J Trauma 1997;43:940-946.
85. Nicholl JP, Brazier JE, Snooks HA. Effects of London helicopter emergency medical service on survival after trauma. BMJ 1995;311:217-222.
86. Greengross P. Effects of helicopter service on survival after trauma: Service is part of a continuum of care (letter). BMJ 1995;311:1164-1165.
87. Maclean D, Kirk CJ, Coats TJ, et al. Effects of helicopter service on survival after trauma: Design of study predisposed to type II error (letter). BMJ 1995; 311:1165-1166.
88. Weil TP. Health care reform and air medical transport services. J Emerg Med 1995;13:381-387.
89. Gearhart PE, Wuerz R, Localio AR. Cost-effectiveness analysis of helicopter EMS for trauma patients. Ann Emer Med 1997;30:500-506.
90. Bruhn JD, Williams KA, Aghababian R. True costs of air medical vs. ground ambulance systems. Air Med J 1993;8:262-268.
91. Smith J. Cost-benefit of hospital helicopters vs. land MICUs. J Aeromed Heath Care 1984;11:16-17.
92. Fischer RP, Flynn TC, Miller PW, et al. Urban helicopter response to the scene of injury. J Trauma 1984;24:946.
93. Shiller WR, Knox R, Zinnecker H, et al. Effect of helicopter transport of trauma victims on survival in an urban trauma center. J Trauma 1988;28: 1127-1134.
94. Cocanour CS, Fischer RP, Ursic CM. Are scene flights for penetrating trauma justified? J Trauma 1997;43:83-88.
95. Jacobs LM, Sinclair A, Beiser A, et al. Prehospital advanced life support: Benefits in trauma. J Trauma 1984;24:8-13.
96. Murphy JG, Cayten CG, Stahl WM, et al. Dual response runs in prehospital trauma care. J Trauma 1993;35:356-362.
97. Abbott D, Brauer K, Hutton K, et al. Aggressive out-of-hospital treatment regimen for severe closed head injury in patients undergoing air medical transport. Air Med J 1998;17:94-100.
98. Trunkey DD. Is ALS necessary for prehospital trauma care? J Trauma 1984; 24:86-87.
99. Sampalis JS, Lavoie A, Williams JI, et al. Impact of on-site care, prehospital time and level of in-hospital care on survival in severely injured patients. J Trauma 1993;34:252-261.
100. Liberman M, Mulder D, Sampalis J. Advanced or basic life support for trauma: Meta-analysis and critical review of the literature. J Trauma 2000;49: 584-599.
101. Cayten CG, Murphy JG, Stahl WM. Basic life support versus advanced life support for injured patients with an injury severity score of 10 or more. J Trauma 1993;35:460-467.
102. Boyd CR, Corse KM, Campbell RC. Emergency interhospital transport of the major trauma patient: Air versus ground. J Trauma 1989;29:789-794.
103. Moylan JA, Fitzpatrick KT, Beyer JA III, et al. Factors improving survival in multisystem trauma patients. Ann Surg 1988;207:679-685.
104. Snow N, Hull C, Severns J. Physician presence on a helicopter emergency medical service: Necessary or desirable? Aviat Space Environ Med 1986;57:1176.
105. Rhee KJ, Strizeski M, Burney RE, et al. Is the flight physician needed for helicopter emergency services? Ann Emerg Med 1986;15:174-177.
106. Anderson TE, Rose WD, Leicht MJ. Physician-staffed helicopter scene response from a rural trauma center. Ann Emerg Med 1987;16:58-61.
107. Schwartz RJ, Jacobs LM, Lee M. The role of the physician in a helicopter emergency medical service. Prehospital Disaster Med 1990;5:31-37.
108. Baxt WG, Moody P. The impact of the physician as part of the aeromedical prehospital team in patients with blunt trauma. JAMA 1987;257:3246-3250.
109. Mackenzie CF, Shin B, Matjasko MJ. Physicians on air medical teams (letter). JAMA 1987;258:2377-2378.
110. Hamman BL, Cue JI, Miller FB, et al. Helicopter transport of trauma victims: Does a physician make a difference? J Trauma 1991;31:490-494.
111. Burney RE, Hubert D, Passini L, et al. Variation in air medical outcomes by crew composition: A two-year follow-up. Ann Emerg Med 1995;25:187-192.
112. Stone CK. The air medical crew: Is a flight physician necessary. J Air Med Transp 1991;10:7-10.
113. Rau W. 1999 medical crew survey. Air Med J 1999;5:27-33.
114. Polk JD, Fallon WF Jr. The use of focused assessment with sonography for trauma (FAST) by a prehospital air medical team in the trauma arrest patient. Prehosp Emerg Care 2000;4:82-84.
115. Polk JD, Fallon WF Jr, Kovach B, et al. The "Airmedical F.A.S.T." for trauma patients—the initial report of a novel application for sonography. Aviat Space Environ Med 2001;72:432-436.
116. Price DD, Wilson SR, Murphy TG. Trauma ultrasound feasibility during helicopter transport. Air Med J 2000;19:144-146.
117. Bahner DP, Yeager S, Werman HA. Ultrasound image quality in the out-of-hospital environment (abstract). Acad Emerg Med 2001;8:568.
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