Annals ofBurns and Fire Disasters - vol., VIII - n. 4 - December 1995

MANAGEMENT PROTOCOL OF BURN PATIENTS DURING AIR EVACUATION

Santos F.X., Sanchez-Gabriel J., Mayoral E., Hamann C., Fernàndez DelgadoJ.

Hospital Universitario del Aire, Madrid, Spain

SUMMARY. The evacuation protocol for the airborne transport of critically burned patients is presented. This protocol is based on the repercussion of air evacuation on the physiopathology of bums. Clinical re ercussions are due to acceleration, vibration, noise and, above pall, altitude. Acceleration is important during take~off and landing, and vibration may be important in helicopter evacuation in the presence of craniofacial traumas. Noise, especially in helicopters, can interfere with in-flight diagnostic and therapeutic maneouvres. Altitude alters atmospheric pressure, partial pressure of ox ygen, and water concentration in inhaled air. In the aircraft we use, atmospheric pressure is between 532 and 550 min Hg at normal flight altitudes. This situation determines the expansion of body gases. Hypoxia seriously aggravates any respiratory insufficiency, especially in the presence of smoke inhalation. The decrease of water concentration in inhaled air imposes an increase in fluid perfusion.,Pre-flight and in-flight levels are analysed, especially with regard to smoke inhalation, pneumothorax and parenteral perfusion.

The objective of this article is to analyse the repercussions of air evacuation on the particular pathology of the critically burned patient, as based on the experience of 63 evacuations by the Spanish Air Rescue Service (Servicio A6reo de Rescate: SAR). Among these repercussions special attention has to be paid to altitude, noise, vibration, atmospheric pressure, and the partial pressure of oxygen. Attention is also paid to problems that may be experienced before transport and to the conditions that may be encountered by,the aircraft crew and attending medical staff.

Our survey concerns critically burned patients evacuated by the SAR between 1987 and 1992. In this period the SAR evacuated 63 critically burned patients in 53 flights, with an average flight time of 2 hours 34 minutes. Patients were considered to be critically burned if they presented at least one of the following conditions: body surface area (BSA) burned over 20%, full-depth burns in more than 10% BSA, history of smoke inhalation, head bums, associated lesions, previous disease (cardiopulmonary, diabetic, neurologic), age over 65 years. The mean BSA burned was 44.3%. A history of smoke inhalation~'was recorded in 21 patients (33.3%); 15 patients. (~3.8%). had associated lesions. Fractures were diagnosed in 18 patients (28.6%), abdominal or thoracic trauma in 22 (34.9%), open and closed cranioencephalic trauma in 7 (11.1%), and open wounds (other than bums) in 33 (52.4%). The mean time between the bum accident and evacuation was 12.5 hours (range 724 hours).
The following aircraft were used: Aviocar CASA-212 (31 flights),' Superpuma AS 332B (18 flights), and CASA235B Nurtanio (4 flights). Table I shows the characteristics of each of these aircraft.

After stabilization of the critically burned patient, with special attention to fluid therapy and the monitoring of urine output, a number of standard procedures should always be followed when air evacuation is attempted.
When strioke inhalation is suspected,' chest radiography and blood gas evaluation must be performed in order to guarantee adequate oxygenation during the flight. Chest radiography is important at this point because it can rule out the possibility of pneumothorax.
If radiography reveals pneumothoraxl, a chest drain must be placed before the flight. The normal drainage system must be replaced by a unidirectional valve system, as closed drainage systems are to be avoided at high altitude. When the chest drain has been positioned, another radiography should be performed, if possible, in order to check the correct positioning of the drain, catheters and endotracheal tube, should these prove necessary. Of the 63 patients we evacuated, only two suffered pneumothorax, both of whom had a chest tube inserted prior to the flight.
As the critically burned patient needs large quantities of fluids,' especially in the first 8 to 10 hours postburn, care is taken to place sufficient intravenous lines, including central lines (subclavian or internal jugular veins). For optimal fluid infusion, it is advisable to use plastic containers which permit the use of pressure cuffs, if these are necessary. This prevents possible perfusion problems due to decreased atmospheric pressure at high altitude.
It is important to place a nasogastric tube prior to initiating air evacuation. The critically burned patient may have paralytic ileus' and as air evacuation is associated with progressive expansion of intraluminal gases, there is increased risk of vomiting and thus of possible aspiration pneumonia. The balloon of the nasogastric tube, as also that of the urinary catheter, should be filled with fluid, not air, in order to prevent rupture of the balloon due to distension of air at high altitude.
It is also important to consider any associated pathology which the patient may have. This helps to prevent complications.
If plaster casts have been placed recently (i.e. less than 24 hours before), these should be split along their entire length and joined by an adhesive strip.
With patients suffering from cardiopulmonary conditions, certain altitude restrictions have to be observed: maximum altitude 10,000 feet; 6,000 feet in cases of recent (8-24 weeks) myocardial infarction; 4,000 feet in cases of pulmonary disease if no oxygen is available; 2,000 feet in cases of cardiac insufficiency. Such patients should be placed with their head pointing in the direction of the front of the aircraft.
An endotracheal tube should be placed prior to takeoff. In-flight endotracheal intubation is difficult, even for experienced staff, especially in the reduced space of the cabin. In patients presenting facial bums, it may be difficult to secure the endotracheal tube. To prevent accidental removal of the tube, it is advisable to use umbilical tape. This can be tied round the base of the tube and then circurnferentially round the patient's head.
Special attention must be paid to the transport of critically burned patients presenting gastrointestinal bleeding. This is usually caused by stress ulcers. Air evacuation is counterindicated in these cases unless sufficient units of blood are carried on board, as the control of such bleeding is exceedingly difficult with cold'saline alone.

There are basically three factors to be taken into account: the aircraft, the crew, and the materials needed for patient care.
Any aircraft intended for use in medical air transport must satisfy a number of basic requirements. The aircraft must be large enough, at least on one side, to permit access of the patient in the prone position, leaving at least 50 cm at the head of the patient in order to provide access for the placing of an emergency endotracheal tube or the manipulation of a tube that is already in position. There should always be at least 65 cm of space between the patient and the roof of the aircraft, to allow for correct administration of intravenous fluids. Apart from the space necessary for transportation of the patient, the aircraft must also have a minimal amount of space available for storage of medical materials. In our experience, helicopters (Superpuma) present the disadvantage of an important lack of space for adequate in-flight manipulation of patients.
The access doors of the aircraft must be large enough to allow easy entry and exit of the patient, enabling the stretcher to be kept horizontal at all times.
The heating system must guarantee a temperature rise from 0 to 18 'C in 10 minutes (necessary for mountain areas or in winter), while the internal lighting of the cabin must be adequate and allow the patient compartment to be independent of lighting in the rest of the cabin. The aircraft must also be equipped with a sufficient number of compatible electric points for the use of all necessary equipment.
If possible, the aircraft should be pressurized in order to reduce or prevent problems caused by pressure variations. Of the aircraft we have used, only the CASA-235B Nurtanio was pressurized.
The personnel in charge of the patient during transport must be well trained in advanced techniques of cardiopulmonary resuscitation. During the flight, they must check the patient's airways, maintain adequate fluid therapy, and monitor urine output, temperature and other vital signs.
The materials used in flight are packed in a medication kit, a resuscitation kit, and an evacuation kit. The medication kit contains drugs, sterile supplies (needles, syringes, tongue blades, povidone-iodine) and non-sterile supplies (razor blades, flashlight, surgical lubrificant, bandage scissors, stethoscope, thermometer, premoistened towelettes). The resuscitation kit includes a tracheostomy set, endotracheal tubes, suction catheters, and syringes. This kit also contains a portable defibrillator-EKG monitor, a bag mask resuscitator, foot suction with tubing, Guedel tubes, McGill forceps, endotracheal tube guides, and a laryngoscope and connections. The evacuation kit consists of a minor surgery set, with sutures, tracheostomy set, disposable sets, sterile gloves, sponges, Foley catheters, Toomey syringes, urometer, nasogastric tubes, fluid and intravenous sets, blood pump, litter straps, tape, medical records and input-output sheets.
For in-flight monitoring, a portable cardiac monitor is especially useful in patients with electric burns or with a history of cardiac abnormities. In-flight monitoring of apical pulse and blood pressure is very difficult because of the noise and movement of the aircraft. It is therefore very useful if the aircraft is equipped with external monitoring devices for these vital signs. All the aircrafts that we used are equipped with a pulse oxymeter and a digital blood-pressure monitor. A pressure-control mechanical ventilator is also available.

Air evacuation is becoming increasingly more common, in both rotary and fixed-wing aircraft. There are however some counterindications, although these are more relative than absolute. Congestive heart failure, severe traumatic abdominal lesions, severe cardiac arrythmias and recent gastrointestinal bleeding are considered relative counterindications for air evacuation by some authors.' Despite the possible problems related to air evacuation, it is a very effective method of transport. It reduces the time necessary to transfer the patient to a secondary centre, and reduces the time during which the patient is not receiving primary hospital care. To this must be added the benefit of the transport of patients over greater distances than is possible with ground transport.
Air evacuation has several associated problems' that are not found in ground transport, or only to a much lesser degree. The five major problems encountered are acceleration, vibration, noise, altitude, and psychological factors.
Acceleration in air evacuation is most marked during take-off and landing. At these moments adequate immobilization of the patient is of utmost importance.' Maintenance of core body temperature is also essential. This can be achieved by multiple layers of sterile dressings and sterile sheets, over which layers of preferably isothermic blankets may be necessary. The patient must be adequately secured to the transporting stretcher by cross-body straps in order to minimize possible injury. This securing may be complicated by bulky packaging, but correct immobilization is essential and is especially important during take-off and landing, when acceleration is greatest. Lesions such as craniofacial traumatisms, embolisms and multiftactures can be aggravated if the patient is not adequately secured to the transporting stretcher.
Vibration as a complicating factor of air evacuation is especially evident in helicopter transport. Helicopters have certain distinct advantages over fixed-wing aircraft in that they have greater manoeuvrability and better access to difficult areas and do not require an airport, but they present a high vibration factor. This can be especially hazardous in patients with associated craniofacial injuries. Routine medical techniques such as apical pulse and blood pressure monitoring are complicated by cabin vibration .8 Helicopter transport also requires correct securing of all intravenous lines and catheters, both to the patient and to the interior of the cabin.
Noise is always present in air evacuation, but is considerably higher in helicopters (80-90 decibels) than in fixed-wing planes. The noise level is not only tiresome for the attending medical staff, greatly complicating routine medical techniques such as auscultation of the patient and evaluation of blood pressure, but also has negative effects on the patient. The patient should be given car plugs or, if conscious, ear phones, in order to facilitate communication.
Altitude is always a problem in air evacuation. At altitude, atmospheric pressure, partial pressure of oxygen, and air humidity are all reduced. Sea level atmospheric pressure (760 ram Hg) decreases to 632 min Hg at 5,000 feet and 532 min Hg at 10,000 feet. Decreased atmospheric pressure causes distension of intraluminal gases, with the possibility of paralytic ileus and vomiting, which may lead to aspiration pneumonia. The decrease in atmospheric pressure is inversely proportional to the degree of pressurization of the aircraft. To prevent problems a nasogastric tube must be inserted, with the balloon inflated with a fluid, not air. If there is pneumothorax, the lower atmospheric pressure will cause distension of air in the pleural cavity, leading to pulmonary collapse. As already said, this must be prevented by inserting a pneumothorax drain prior to transport.
The decreased partial pressure of oxygen can cause hypoxia problems, which are especially hazardous in patients with pneumonia and other forms of respiratory insufficiency (such as that caused by smoke inhalation, which is frequently seen in bum patients), as well as congestive heart failure. In these cases, oxygen must be given through masks or by endotracheal intubation. Owing to the confined space and the movement of the aircraft, in-flight endotracheal intubation is extremely difficult, even in experienced hands. If intubation is required, it must therefore be performed prior to take-off.
The lower humidity of air at higher altitudes leads to dryness of the respiratory tract, which necessitates humidified oxygenation. There is a higher fluid demand, and this requires greater fluid perfusion in order to maintain an acceptable urine output of at least 20-40 ml/hour. To provide high perfusion, in-flight pressure pumps are used to facilitate fluid inflow.
Last but not least, there is also a considerable psychological factor in air evacuation. One major aspect is fear of flying, which can lead to great anxiety. This may result in aggressive behaviour and lack of co-operation from the patient. This stressful situation may lead to hyperventilation, which puts an additional strain on oxygenation and may lead to acid-base imbalances. It is useful to inform patients of each step in the transport in order to put them at their ease. Sedation may be required if the patient cannot be adequately calmed, although this entails greater monitoring of respiratory functions.
In all cases of air evacuation, the medical staff must keep up an extensive in-flight report.' This report should start on day 0 hour 0, i.e. at the moment of the bum accident. Extensive information about the mechanism of the burn injury (electrical, scalding, chemical, etc.) should be noted, along with an accurate assessment of the percentage of burned BSA and burn depth. The in-flight report should include details of all treatment received by the patient at the primary care facility. Information about associated or previous pathologies is also essential. Of special importance here is a previous history of cardiopulmonary diseases, as smoke inhalation is often present in burned patients: it is very important to note this factor in the in-flight report. In addition to these aspects, the report should include an accurate record of all medication given during the flight, as well as a record of the type and quantity of fluids administered. Urine output and fluid balance must be regularly updated. Finally, the report must provide information about any in-flight complications. The report must be completed during the flight and handed over to the physician taking charge of the patient on arrival at the secondary care centre.
Air evacuation of major burn patients is a complicated matter and can entail many problems. Whenever possible, these patients should therefore be accompanied by a physician and an experienced nurse or paramedic, all of whom must be well trained in advanced life-support techniques.

RESUME. Les auteurs présentent leur protocole pour l'évacuation aérienne des grands brûlés, Ce protocole se base sur les répercussions de l'évacuation aérienne sur la physiopathologie des brûlures. Les répercussions cliniques sont causées par l'accélération, la vibration, le bruit et surtout l'altitude. L'accélération est importante pendant le décollage et l'atterrissage, et la vibration peut être importante dans les évacuations en hélicoptère en présence de traumatismes craniofaciaux. Le bruit, surtout dans les hélicoptères, peut entraver les manoeuvres diagnostiques et thérapeutiques en vol. L'altitude modifie la pression atmosphérique, la pression partielle de l'oxygène, et la concentration hydrique de l'air inhalé. Dans les avions que les auteurs utilisent la pression atmosphérique varie entre 532 et 550 mm Hg aux altitudes normales de vol. Cette situation provoque l'expansion des gaz corporels. L'hypoxie augmente toute insuffisance respiratoire, particulièrement dans les cas d'inhalation de fumée. La diminution de la concentration hydrique de l'air inhalé impose une intensification de la perfusion de liquides. Les niveaux avant et pendant le vol sont analysés, surtout pour ce qui concerne l'inhalation de fumée, le pneumothorax et la perfusion parentérale.

BIBLIOGRAPHY

1. Pérez Ribelles V., Laguardia Chueca J.: Aviocar C-212. Empleo sanitario. Medicina Militar: 621-6,1988.
2. Mazzolem F.: Therapeutic priorities in fire disasters. Ann. Medit. Burns Club, 1: 152-4, 1988.
3. Budassi S.A., Barber J.: Burn Trauma. In: "Mosby's Manual of Emergency Care", C.V. Mosby Company, St. Louis, Toronto, 1984.
4. Ortiz Garcfa P.J., Ranget Velasco C.S.: Evacuaciones sanitarias de quemados graves: estudio retrospectivo en un centro especializado de caracter national. Cit. Pldst. lbero-Latinoamer., 11: 251-8, 1985.
5. Herrera Martf J.A.: SAR: el pr6ximo futuro. Rev. Aerondutica y Astrondutica: 1202-8, 1988.
6. Simko S.: Reflections on the organization of mass burn treatment.Acta Chir. Plast., 23: 197-200, 198 1.
7. Mollicone S.: The contribution of the air force to civil defence. Ann. Medit. Bums Club, 1: 168-70, 1988.
8. Moylan J.A.: First aid and transportation of burned patients. In: "The Art and Science of Burn Care" (ed. John A. Boswick Jr), pp. 41-4, Aspen Publications, Rockville, Maryland, 1987.
9. Quetglas Marim6n A., Ortiz Garcfa P.J.: Apuntes Para el transporte de los quemados. Cit. Pl6st. lbero-Latinoamer., 11: 233-48, 1985.