Air ambulances can play an important role in transporting patients with time critical injuries and conditions to medical facilities and providing patients with advanced care while en route. Air ambulances transported more than 270,000 patients in 2008, and their use is widely believed to improve the chances of survival for trauma victims and other critical patients. Composing more than 80 percent of air ambulance aircraft, helicopter air ambulances transport patients from the scene of an accident to a hospital or perform short-distance interhospital patient transfers. Because fixed-wing aircraft only fly between airports, they are not typically used to transport injured patients from an accident scene. Patients are transported by ground to and from the airport. Fixed-wing air ambulances generally perform more long-distance interhospital transports, often moving patients from a hospital to a distant specialized facility. Just over half of air ambulance transports are for moving patients between hospital facilities, one-third are for transporting victims from the accident scene to a hospital, and the remainder are for other purposes, such as organ transports or specialty care flights such as for pediatric and neonatal patients. Most air ambulances carry a pilot and a two-person medical crew. The medical crew may include a physician, nurse, paramedic, emergency medical technician, or other medical personnel. According to AAMS, the typical medical crew includes a critical care nurse and a paramedic. A critical care nurse has specialized training in responding to life-threatening health problems, such as those faced by many patients who are transported on air ambulances. Paramedics represent the highest licensure level of prehospital emergency care in most states, as they have enhanced skills and can administer a range of medications and interventions. Other caregivers and physicians may be added to a medical crew if the patient’s condition necessitates further care. In the air ambulance industry, the business model is generally defined by the entity that owns or contracts for the aviation and medical services that are provided. Air ambulance providers generally use one of the following three business models. Hospital-based: a hospital generally controls the business by providing medical services and staff while usually contracting out for the aviation component, including the pilots, mechanics, and aircraft. Independent: operations are not controlled or run by a specific medical facility. Independent providers may directly employ, or can contract for, the medical and flight crews to provide air ambulance services. Government operator: a state or local government or military unit owns and operates the air ambulances. However, a large number of variations exist within these structures. Some providers have adopted a “hybrid” model or have established joint ventures with hospitals. Air ambulance companies receive payment for transports from several sources, including private health insurance, government programs such as Medicare and Medicaid, and the patient. While industry revenue and payment data are not widely available, we obtained data on the percentage of total income that four air ambulance providers receive from each source. (See fig. 1.) For these four companies, private insurance companies or Medicare paid for most of the transport costs. A relatively small percentage of the costs were paid for by the patient themselves. From 2002 through 2006, the Centers for Medicare and Medicaid Services, the agency within the Department of Health and Human Services that administers Medicare and Medicaid, phased in a national fee schedule for air ambulance providers as a part of a series of Medicare payment reforms that Congress mandated in 1997. The national fee schedule redistributed, on a budget-neutral bases, payments among various types of ambulance services. Prior to 2002, Medicare reimbursement differed depending on the air ambulance provider’s business model: hospital-based providers were reimbursed based on reasonable costs, while independent providers were reimbursed based on reasonable charges. This policy contributed to wide variation in the reimbursement rate for the same service, with hospital- based providers generally receiving higher reimbursement than independent providers for similar services. The new national fee schedule established one payment rate for fixed-wing transports and another rate for helicopter transports. The fee schedule also provides higher reimbursement for transports in rural areas, but it does not differentiate payments according to the business model followed, the size of the aircraft used, or the level of medical or safety equipment on board. In addition to the revenue they receive from transports, air ambulance providers may receive or generate income for their operations from other sources. For example, hospital-based providers may receive funding from the hospital, and some independent air ambulance providers have established membership programs that generate income from annual fees. Government operators may receive funding through taxes or surcharges. For example, Maryland’s government-operated air ambulance service receives funding through a surcharge on state motor vehicle registrations. From 1999 through 2008, the number of patients transported by helicopter air ambulances increased from just over 200,000 to over 270,000, or about 35 percent, and the number of air ambulance helicopters increased from 360 to 677, or by about 88 percent. The data also show that between 2007 and 2008 there were an increasing number of helicopter air ambulances and a decreasing number of transports. (See fig. 2.) We were unable to determine whether the downward movement in 2008 represents a trend because 2009 data on patients transported were not available. The number of air ambulance helicopters varies widely by state. (See fig. 3.) Most states have multiple helicopters based in their state. Vermont and Rhode Island have none, but their air transport needs are served by providers in bordering states. Since 1999, the structure of the air ambulance industry has also changed. In the past, most air ambulance providers were hospital-based, whereas today, about half the providers are independent, with no support from hospitals in terms of ownership, risk, and financial support. According to industry stakeholders, a variety of factors contributed to the industry’s growth and structural change. The downsizing or closing of some community hospitals, according to stakeholders, resulted in longer transports to get some patients to hospitals, making it more advantageous to use air ambulances that could transport patients over longer distances more quickly than by ground ambulances. Similarly, the establishment of regional medical facilities, such as cardiac and stroke centers that provide highly specialized care for critically ill patients, encouraged the use of air ambulances, again because they could transport patients more quickly from outlying areas. Finally, implementation of the Medicare fee schedule provided those wishing to provide air ambulance services a degree of predictability for Medicare reimbursement, which stakeholders noted enabled air ambulance providers to develop more accurate financial plans. The growth in the number of helicopters and their movement into communities have generally made them more available to those in need. According to some stakeholders, having multiple air ambulances in an area increases the industry’s capacity to meet regional needs. For example, if one helicopter is unavailable because it is undergoing scheduled maintenance or responding to an air medical transport request, another helicopter in the same region is more likely to be available. Additionally, with more air ambulances available in rural communities, rural ground ambulances may be involved less frequently in transporting patients over long distances, and rural communities are less likely to be left without an ambulance or EMS crew. Providers also relocated air ambulance bases, moving them from hospitals into surrounding communities and thereby extending their availability. (See fig. 4.) A 2005 nationwide study of access to trauma centers in the United States found that 84 percent of the population had access to a Level I or II trauma center within 60 minutes. Of that population, almost 28 percent could only access those trauma centers in an hour or less because they were located within the coverage of an air ambulance. Stakeholders concerned with the growth in the industry, noted that the increase in the number of helicopters has been focused in areas that already have multiple air ambulance services while rural areas remain underserved. They said that ensuring the availability of air ambulance services in rural areas is problematic because covering a large, sparsely populated geographic area affects profitability and impacts companies’ ability to provide services in these areas. Stakeholders concerned with industry growth believe that uncontrolled growth of air ambulances in a region leads to medically unnecessary use— that is, when an air ambulance is dispatched for a patient whose injury or illness is not severe enough for the patient to need air transport. One stakeholder group compared data on the severity of patients’ injuries and discharge rates, developed by Arizona’s Department of Health Services, with similar data for a Level I Trauma Center in New Hampshire, and an air ambulance service in Boston. According to their analysis, the injuries of patients transported in Arizona, a state with a comparatively large number of helicopters, were less severe than those of patients transported in the two other states that have fewer helicopters. However, the comparison does not examine other factors involved in decisions about how to transport patients, including transport distances, who makes the transport decision, and what protocols guide the decision maker. Additionally, the decision to request an air ambulance is generally made by the attending physician at a hospital or by first responders at an accident scene. Concerns about medically unnecessary use of air ambulances have existed since the early 1980s. We identified 32 studies examining triage criteria using data collected from as early as 1975 to as recently as 2008. Fifteen study authors conclude that further measurement indices are needed to better identify over- and undertriage of patients transported by air ambulance. Because triage protocols and patterns of air ambulance utilization have changed considerably in the past 30 years, early reports must be interpreted with caution and their relevance to current triage protocols and air ambulance is unclear. It is also important to consider these studies in their historical context. Numerous guidelines on appropriate use of ambulances have been published. In 2006, the American College of Emergency Physicians and the National Association of EMS Physicians (NAEMSP) issued Guidelines for Air Medical Dispatch that built upon earlier guidelines published by NAEMSP, AAMS, and the American Academy of Pediatrics. The 2006 position statement recognized the continuing debate surrounding air medical transport and noted that research regarding the appropriate deployment of complex medical care systems was in its infancy.