Introduction
Air medical transport includes fixed wing (airplanes) and rotor wing (helicopters) aircraft. They are utilized in situations for transporting patients where ground transportation (ambulances) are less effective. For example, helicopters are often used to transport critical trauma patients since time is an important factor in improving chances of survival. Airplanes are essential for carrying patients between states and countries. However, many factors have to be taken into consideration when choosing to utilize air medical transport.[1][2][3][4][5]
Issues of Concern
Advantages and Disadvantages
Air medical transport provides numerous advantages over ground transport, namely increased speed and maneuverability. Ground transport is limited by factors such as availability of roads, road conditions, and traffic. Ground transport also travels much slower than air transport, especially when compared to fixed-wing aircraft. However, there are also disadvantages to air transport. These disadvantages may be common to both fixed wing and rotor wing aircraft, or specific to each type. The common disadvantages are an increased cost which depends on many factors such as staffing, type of aircraft, and distance of transport. The cost of operating air medical transport is also very high because the aircraft itself can cost several million dollars, and the maintenance is very strictly regulated. Air transport is more susceptible to weather conditions than ground transport, usually more so in rotor wing aircraft. Weight also has to be carefully calculated since the engines are only able to produce a finite amount of power. An aircraft that is overweight can end in disaster.
Safety
Another disadvantage of air medical transport is that it is inherently more dangerous than ground transport, especially in helicopter transport. There is no specific data that directly compares air transport to ground transport. However, some studies look at each individually. In a 20-year period between 1992 through 2011, there were approximately 4500 ambulance accidents. Of these accidents, 29 resulted in fatal injuries. In a 10-year period between 1998 through 2008 there were 146 helicopter accidents, and of these 50 (34%) resulted in fatal injuries. What this tells us is that accidents involving air transport are more likely to be fatal than ground accidents. The percentage of accidents that are fatal are roughly the same in fixed-wing accidents as well.
Characteristics of Air Medical Transport
Aircraft can have a single engine or multiple engines. Helicopters typically have either 1 or 2 engines. With 2 engines, a helicopter can carry more weight and travel at faster speeds. However, they also consume more fuel which increases the cost. They also cost more for maintenance. Airplanes usually have more than one engine since typical single-engine airplanes are not big enough or powerful enough to transport a patient plus the crew and required equipment. Having multiple engines also adds an increased safety factor since 1 engine can malfunction and the aircraft still has a working engine to use to land safely.
Helicopters are ideal for transporting critical trauma patients because they are more effective in decreasing the time of transport to a trauma hospital. This is important because, for many critical trauma patients, the most important factor in decreasing mortality is getting them quickly to an operating room with a trauma surgeon. Patients have to be considered a critical trauma patient (often called a “trauma alert”) for consideration of helicopter transport. Following is an example of adult trauma alert criteria that is used by Holmes Regional Medical Center in Melbourne, Florida.
One of the following:
Active airway assistance required beyond administration of oxygen
Heart rate greater than 120 without radial pulses
Systolic blood pressure less than 90
Best motor response less than or equal to 4, or a total Glasgow coma scale less than or equal to 12
Second or third-degree burns on greater than or equal to 15% of body
Amputation proximal to wrist or ankle
Penetrating injury to head, neck or torso excluding superficial wounds where the depth of the wound can be determined
Two or more long-bone fracture sites (humerus, radius/ulna, femur, tibia/fibula)
Paralysis, loss of sensation, or suspected spinal cord injury
Judgement of EMT, paramedic, or another healthcare provider
Two of the following:
Respiratory rate greater than or equal to 30
Sustained heart rate greater than or equal to 120
Glasgow coma scale best motor response equal to 5
Major degloving injury or flap avulsion greater than or equal to 5 inches
Gunshot wound to the extremity
One long-bone fracture from a motor vehicle collision or fall greater than or equal to 10 feet
Ejected or thrown from any vehicle (including ATV, motorcycle, moped, or truck bed)
Steering wheel deformity
Helicopters can land close to the scene of the incident, often landing on roads or open fields. These landing areas usually have to have a size of at least 100 feet by 100 feet and must be relatively flat and free of debris. First responders will often mark the area for the helicopter crew, and provide security to keep bystanders from approaching the landing area. Ground crews need to be trained on landing zone safety so that they do not put themselves or the helicopter crew in danger by being struck by the main rotor or tail rotor. Helicopter crews are trained on exiting and entering the aircraft on the scene which usually requires approval by the pilot. This can occur with the aircraft shut down or with the rotors turning, which is called a hot load or hot offload. The pilot has the final say on if the landing zone is safe for landing. Many obstacles can create a safety hazard such as proximity to power lines, crowds of people, or the type of landing surface. Landing in a muddy field can cause the landing gear or skids to sink into the mud, making it difficult to take off. Loose objects or debris can also be a hazard because the downwash of the main rotor blades can blow these objects into the air, causing them to get sucked into the rotor blades and/or engines.
Helicopters can also be utilized to transfer patients from one hospital to another. This is usually because the patient needs to be transferred to a specialized care service which is not available at the sending hospital. Examples of this would be a burn center, cardiac cath lab, or even to be placed in an intensive care unit. Hospitals usually have a landing pad for helicopters, which are generally safer than landing at a scene. Helicopter landing pads are placed in a safe area away from buildings or power lines, are flat and made of solid materials such as concrete, and have appropriate markings and lighting. Landing pads can also be placed on rooftops. Landing pads are such an ideal landing surface that patients from a scene will sometimes be transported by an ambulance to the closest landing pad if a suitable area cannot be found for landing near the scene.
Weather conditions are an important consideration for air medical transport. Helicopters are susceptible to heavy weather conditions such as strong winds or heavy snowfall. Another important aspect of weather conditions is visibility. Pilots have a set of regulations called Visual Flight Rules (VFR) or Instrument Flight Rules (IFR) which are set by the Federal Aviation Administration. Helicopters operating under VFR must have clear visibility of several miles depending on the altitude and type of aircraft. An example of this is helicopters operating during the day under 1200 feet must have visibility of one mile. The purpose of this is to allow the pilot to be able to see and avoid other aircraft or structures such as towers. Airplanes also operate under VFR, but since they are faster and operate at higher altitudes than helicopters, they have increased visibility requirements, up to five miles. VFR also require aircraft to keep a minimum clearance from clouds such as 500 feet below, 1000 feet above, and 2000 feet horizontally.
If an aircraft flies outside of the minimum requirements of VFR, then they have to fly using Instrument Flight Rules. This is considered flying “in the clouds.” To be certified to fly IFR, aircraft have to have specific equipment which consists of several navigational aids. Pilots must also have special training because it can be difficult to navigate strictly using instruments without being able to see an outside reference for spatial orientation. Aircraft also can only land at places with an Instrument Landing System, which is usually only at airports. This means that helicopters cannot land at a scene or landing pad using IFR. Some medical transport helicopters are not equipped to fly in IFR. Because of this restriction, medical transport helicopters are often unable to accept flights when there is poor visibility.
Airplanes also have special considerations. The most obvious being that they require a runway for takeoff and landings. The exception to this is a seaplane that requires a large body of water. This requires the patient to be transported by ground to the airport, and then again picked up at the destination airport for transport to the final medical facility. Airplanes have a larger range of travel than helicopters. Because of this, airplanes are usually used when a patient must be transported a long distance, for example, between countries. Airplanes also have the ability to travel at much faster speeds then helicopters.
Another consideration for both fixed and rotor wing aircraft is physiologic changes due to altitude. Boyle’s law states that the volume of a gas increases when the pressure decreases at a constant temperature. As an aircraft ascends in altitude, there is a proportional decrease in the surrounding atmospheric pressure. At sea level, atmospheric pressure is 14.7 pounds per square inch (psi) (101 kPa). At 10,000 feet, it is 10.1 psi. What this means is as an aircraft ascends, any gasses on board will increase in volume. An example of this is a patient with a pneumothorax could have an increase in the size if they do not have a properly functioning tube thoracostomy. Another issue that has to be considered is equipment that has gas-filled cuffs, such as endotracheal tubes. If the volume inside the cuff is allowed to expand, it could cause damage to the trachea including pressure necrosis. Airplanes are more susceptible to altitude-related problems since they travel at higher altitudes. However, they have pressurized cabins which help correct these problems. Helicopters are still susceptible to altitude-related issues since even at an elevation of 1500 feet, atmospheric pressure decreases to 13.9 psi.
The crews of air medical transport have varying types and amount of personnel. They may have one or two pilots, and medical personnel can consist of combinations of nurses, paramedics, physicians, or respiratory therapists. These crews have to have specialized training which includes a course on Air Medical Resource Management. This is a management system which makes optimum use of all possible resources for flight crew personnel to secure safe and efficient operation. The goal is to diminish unfavorable events due to human error. Crews also may have other training specific to the type of equipment on their specific aircraft, for example, night vision goggles. Medical personnel sometimes have an expanded scope of practice. An example of this is paramedics or nurses having the ability to place chest tubes. This is often necessary to effectively treat patients who are a long distance from the definitive care they may need. Medical personnel must be very proficient in all aspects of their scope of practice since almost all of their patients are high acuity.
Clinical Significance
The decision to use air medical transport has many considerations. Ultimately, will transporting the patient by helicopter or airplane benefit the patient? While aircraft can travel at much faster speeds than ground transportation, there is a loss of time for setting up a landing zone (or transporting to an airport) and evaluation by the flight crew. Would it be a comparable transport time just to “load and go” by ground transportation? Also, will the patient’s condition be better served by a higher level of care or greater scope of practice that might be provided by the air medical transport crew? The benefits have to be weighed against the risks.[6][7][8][9]
