Individual hospitals, hospital systems, or private for-profit enterprises run most U.S. civilian air transport programs. Because helicopters are expensive (ranging from $750,000 to more than $5 million each) and other aviation needs (e.g., maintenance, pilot training) are also resource intensive, most hospital-based programs lease their helicopters from vendors. The air medical program typically provides and equips communications and medical personnel, whereas the aircraft vendor supplies the helicopters, pilots, and maintenance personnel. Although costs vary depending on geographic region, patient case mix, equipment and aircraft used, and even the methods used for their calculation, annual operating costs for a rotor-wing service typically exceed $2 million.
Safety is an overriding consideration for air transport. Optimization of safety begins well before an actual air transport, with training of the flight crew and of those who interact with them at scenes and hospitals. Training is especially important for scene responses, in which the helicopter may be landing in an unknown area with more nearby obstacles (e.g., wires, trees) than the hospital helipad. Scene setup (depending on the aircraft, an area of up to 100 × 100 ft is required) and demarcation, as well as safety of nearby personnel, must be taught to ground EMS services and others who call for helicopter EMS transport. In addition to providing training for referring agencies, helicopter EMS pilots and medical crew should undergo both initial and recurrent safety training. For added protection, most helicopter EMS programs have followed the lessons of the military experience and adopted injury-prevention maneuvers such as the use of helmets and fire-resistant clothing. As another safety issue, the pilot should be "blinded" to the nature of the call during mission planning; this eliminates the introduction of acuity-related subjectivity as the pilot considers whether the mission should be accepted.
Safety is partially behind the transition of helicopter EMS programs from single-engine helicopters with visual flight rules capability to twin-engine helicopters that can fly under instrument flight rules conditions. The latter aircraft have greater lifting capacity, range, and speed and usually can execute controlled landings in the event of failure of one engine. A visual flight rules aircraft can fly only during good visibility, whereas instrument flight rules aircraft operate safely in poorer conditions; both comply with visibility limitations imposed by the Federal Aviation Administration, but the instrument flight rules helicopter has fewer restrictions. If the pilot unexpectedly encounters bad weather during a flight, an instrument flight rules helicopter (as compared with a visual flight rules aircraft) has a better chance of completing the mission successfully and safely. Due to the complexity of instrument flight rules operations, some programs (especially those with frequent bad weather periods) have elected to use two-pilot instrument flight rules.
Air medical programs operate under rules established by the national aviation authority—in the United States, the Federal Aviation Administration. Additionally, the industry itself has set forth stringent standards under the auspices of the Committee on Accreditation of Medical Transport Systems. On request, the Committee on Accreditation of Medical Transport Systems performs site visits of air medical programs to certify that they comply with strict safety and operational (as well as clinical) standards. As of January 2012, 148 U.S. transport programs were accredited by the Committee on Accreditation of Medical Transport Systems.
The primary considerations regarding medical members of the flight crew are crew configuration and training. Although there are few absolutes with regard to optimal configuration, initial and recurrent training are at least as important as the credentials of the flight team members.
The air medical team can have multiple compositions: nurse–paramedic, nurse–nurse, nurse–physician, or nurse–respiratory therapist. These differences may be one reason that the literature has failed to answer definitively the seemingly simple question of whether a physician should be on board the helicopter. Studies done outside the United States, where physician staffing is more prevalent, have failed to show outcome improvement associated with physician staffing of helicopter EMS programs.1,2 Most U.S. programs agree that physicians are not a necessary component of helicopter EMS crews, and individual program staffing configurations generally have remained stable during the ongoing debate on optimal team makeup.
For a number of reasons, it is unlikely that further efforts to define the optimal crew configuration will result in a consensus. The capabilities of most U.S. nonphysician crews represent an extended scope of practice. For instance, flight paramedics and/or nurses frequently are credentialed to perform such procedures as neuromuscular blockade–assisted endotracheal intubation and cricothyrotomy. This example of extended practice scope is important, given the importance of prehospital airway considerations and the fact that flight crews represent a highly trained group with particular expertise in this area. Reported success rates for nonphysicians are as high as 94.6% for drug-assisted and 97.7% for rapid sequence intubation–assisted endotracheal intubation and 90.9% for surgical cricothyrotomy.3 The ability of nonphysicians to perform advanced procedures—and to perform them well—blurs the procedural skills demarcation between physician and nonphysician crew. Physician cognitive contributions are inherently difficult to quantify or associate with patient survival.1,2
At this time, the best recommendation with regard to crew configuration is for programs to continue to do what works for them, as the literature does not report the superiority of a particular model. Most U.S. programs perform a variety of scene and interfacility missions for trauma and nontrauma indications, so the nurse–paramedic configuration, combining the complementary skills of prehospital and hospital-based practitioners, is most popular in the United States. Some transport population heterogeneity can be addressed by the accommodation of extra crew members (e.g., neonatal nurses, intra-aortic balloon pump technicians) when logistics allow. Regardless of the background of the air medical crew, initial and recurrent training in both cognitive and procedural skills is necessary to ensure an optimal level of care.
ENVIRONMENTAL FACTORS OF AIR TRANSPORT
Patient care in any transport vehicle differs from that provided while the patient is on a hospital stretcher. Vehicle vibrations, bumpy rides, noise, physiologic stress, ergonomic constraints (Figure 3-1), and motion sickness are among the factors that can affect monitoring and interventions.
The patient care compartment in a Dauphin II helicopter.
The impact of most vehicle-related issues in helicopter EMS can be eliminated, or at least reduced. Some solutions are easy (e.g., visual rather than aural alarms on ventilators), but flight crews must learn to "work around" other limitations (e.g., perform preflight intubation on patients who appear likely to deteriorate). Some problems will be specific to a service's particular aircraft, mission profile, or crew background. Individual program patient care protocols should take into account the service's equipment and personnel-related capabilities and limitations.
One transport-related issue that cannot be avoided is the question of altitude and its potential effects on the patient and the crew. In fact, altitude considerations vary with location—a Denver-based program has concerns that are different from those of a Miami service. Environmental conditions also have an impact on altitude considerations, because aircraft operating under instrument flight rules frequently fly at higher altitudes than those operating under visual flight rules. Of course, fixed-wing transports have more pronounced altitude considerations.
Helicopter (or fixed-wing) altitude and environment have potential effects on patient pathology as well as the crew's ability to monitor and care for the patient. Helicopters generally transport patients at about 1000 to 3500 ft above ground level (not necessarily sea level), although sometimes these altitudes are increased for instrument flight rules flights or for clearing of obstacles or terrain. Therefore, altitude-related problems such as hypoxemia, dehydration, and low temperature tend to be mild or relatively easily to overcome. However, geographic differences are important. Some western U.S. programs fly with supplemental oxygen for the medical crews.
Pressure-related problems related to Boyle's law (the volume of a gas increases when the pressure decreases at a constant temperature) may represent the most important consideration for helicopter-transported patients. For example, even the relatively low transport altitude range for helicopter EMS may affect patients with certain diagnoses (e.g., decompression sickness, cerebral arterial gas embolism) or instrumentation (e.g., tamponading devices for esophageal variceal hemorrhage). Endotracheal intracuff pressures increase an average of 33.9 cm of water at a mean altitude of 2260 ft.4 This could raise the cuff pressure above the perfusion pressure of the tracheal mucosa, leading to injury. Hand-held commercially available devices can be used to keep cuff pressure within the target range of 20 to 30 cm of water. The devices are held in one hand and connected to the cuff inflation port. An inflation bulb can be used to further inflate the cuff or an air-release button can be used to remove air while the cuff pressure is simultaneously measured by the device.
In some cases, an understanding of altitude issues is important in preventing complications. To minimize aspiration risk, gastric intubation should be performed for unconscious patients transported by air. Alternatively, understanding of the relevant science can be used to prevent overreaction to potential barometric risks. For example, not all patients with small pneumothoraces who do not otherwise require tube thoracostomy require pretransport chest decompression simply because they are to be transported by air.