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Medical Progress Indian Pediatrics 2000;37: 853-871 |
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Transfer of Sick Children by Air |
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N.N. Aggarwal and Sandhya Aggarwal*
Air travel today has become the fastest, safest and the most convenient mode of travel for those who can afford it. More than 10 million in India and 400 million people in US fly annually aboard commercial aircraft. Airline resources have forecasted that the airline fleets will double in India in next 20 years from the present 105 aircraft to 224. Although, the air passenger service by airships had started in 1910 in Germany, the pediatric air trans-portation in powered aircraft had started sometime in 1930s, and has grown tremen-dously thereafter. While the exact statistics about infants, babies and grown up children travelling by air are not known, it could be an easy assumption that about 1/10 of travelling population is constituted by children. Majority of these children are healthy and adapt well to exposures to moderate cabin altitudes and pressurization in the aircraft. However, some of the sick children may not be able to withstand air travel due to altered physiological balance primarily by the disease process itself with additional set of freshly imposed aviation stresses. It seems contrary to the belief that any one, who can be evacuated by a fast taxi or an ambulance on the ground, can be evacuated by air. The number of sick children evacuated by air has been increasing by each year for specialized treatment abroad and within the country. The commoner conditions for which the specialized treatment abroad has often been sought, include patent ductus arteriosus (PDA), thalassemia major, a variety of leukemias, hyaline membrane disease (HMD), broncho-pulmonary dysplasia (BPD), invasive/operative procedures like bone marrow transplants (BMTs), correction of congenital heart disease (CHD) lesions, organ transplantation, pro-longed comatose conditions, various types of carcinomas besides several others. It is important to realize that many of these transfers are primarily due to failed local treatment, desperation and under life threatening conditions. Under these circumstances, the patient requires to be transferred in any stage of seriousness. A successful aero-medical transfer requires good knowledge of aviation-stressors and induced problems. These generally include the altered aircraft environ-ment at altitudes, difficulties in use of equip-ment and monitoring devices in pressurized and unpressurized cabins, altered medication schedules under time zone changes especially on international flights, besides many others. The primary responsibility of safe air transfer lies with the treating or escorting physician/pediatrician and not with the airline providing the air carrier. For all medical/medicolegal purposes, it is assumed that as a specialist he understands the physiopathological, clinical and aero-medical prognostic effects as well as safe use of equipment involved in such a transfer as to ensure a successful transfer. The paper discusses the factors affecting general handling, use of equipment and the procedures in carriage of the sick child during air transfer.
The Cabin Environment Commercial airliners usually cruise between 22,000 ft (6,706 m) and 44,000 ft (13,411 m) above mean sea level (AMSL) to optimise their operational efficiency. At these altitudes, the ambient air outside the aircraft is rarer at lower atmospheric pressures, and therefore is incompatible with sustenance of life. Consequently, most of the modern passenger transport aircraft designed for cruise in upper airspace are pressurized, as to achieve an effective cabin altitude between 5,000 ft (1,529 m) and 8,000 ft (2,438 m). The Federal Aviation Authority (FAA) of US and similar other civil aviation regulatory bodies require the airliners to maintain 8,000 ft cabin altitude at the highest operating altitude(1). This much pressurization is required for the well being and survivability of passengers in hypoxic environment at high altitudes. The helicopters, small commuter planes and air ambulances cruise at medium to low altitudes depending upon their altitude ceiling, operational capabilities and type of commitments such as inter or intra-city movements including dedicated air transfers such as for emergency or specialized treatment. Their flight altitudes could lie anywhere between 500 to 22,000 ft AMSL. The aviation stresses at these altitudes include exposure to altitude hypoxia, partly recycled cabin air, its contamination by smoke, deodorants, deinsect-ization sprays etc., anxiety and hypoxia induced hyperventilation, low temperatures, expansion of gases in the body cavities, noise and vibration, accelerative and decelerative stresses, turbulence, prolonged sitting/lying in cramped space besides some others. Some of these may have rarer but serious and life threatening relevance to air transfer in commercial airliner such as decompression sickness. The situation gets further complicated by a number of limitations experienced in the use of hospital monitoring equipment in aviation environment, to which the accompanying doctor is not used to. Thus any of the clinical condition, which is likely to get worsened by additional hypoxia, pressure changes expansion of gases within enclosed body/tissue spaces, motion sickness, psycho-logical stress including fear of flying needs special precautions and measures. These factors could be quite stressful for the patient as well as for the doctor evacuating the patient for the first time. For a sick child, these factors are additionally stressful along those already imposed by the disease process, which gets further compounded. Comatose children may pose extremely challenging situation. In recent times, yet additional aero-medical concerns have come up with increasing use of new generation non-invasive detection methods of lesions in awaiting to be born babies. Usually, there are a number of pre-requisites for air transfer of casualties including administrative, medical and equipment clearances, which are slightly different for international and domestic air transfers. Many domestic airlines are not adequately equipped and geared for such eventualities, and therefore may not be able to observe time-tested aeromedical concepts and principles. The basic-most in-flight medical care starts with the knowledge of child restraint system for small as well as grown up children.
The aircraft environment is generally not a problem for children except in few conditions. They may, therefore, be accepted as passengers from birth itself. However, the British Aero-medical Practitioners Association recommends, that a minimum of 48 hours should be allowed between birth and flying. In US, the newborn babies are recommended not to fly within one week of delivery(2). This period is kept essentially to be sure of health and stability of the infant, and freedom from postpartum conditions such as acute respiratory distress syndrome, metabolic disturbances, congenital defects, etc., for which special consultation of an Aerospace Medical Specialist may be taken. Many IATA (International Airline Transport Association) members and a few domestic airlines have such specialists on their regualr medical panel. A healthy neonate can undertake flying, when escorted by medical attendant with adequate in-flight support(3). Most airlines accept children below 2 years as lap passengers. Young children below six years are not accepted on airline without an accompanying adult. The neonates seem to tolerate air travel well and be less susceptible to early stages of oxygen lack at altitudes, compared to adults. However, once the symptoms of hypoxia are observed, the subsequent decline in their condition is much more rapid. Routinely, it is the apparently stable children with chronic disorders of childhood such as asthma, sickle cell anemia, seizure disorders, congenital heart disease and orthopedic disabilities such as non-healing fractures, who take to air travel in commercial flying with or without medical consultation, albeit having high risk of inflight deterioration. For any assistance at the airport and inflight medical/physical assistance, the medical attendant of the sick is invariably required to forward the relevant information on prescribed ‘Medical Information Form’ (MEDIF) to the airline special services. The medical authorities of the airline decide acceptance of the sick for air travel on the information provided by the attending doctor. The airline is not responsible for any mishap, in case the provided information happens to be false, or the medical attendant does not seek appropriate inflight help such as available equipment or oxygen, when actually the condition of the sick demanded the same. In such circumstances, the airline at its best offers only the first aid and pages for an onboard physician, in case he volunteers to help. The accepting airline medical authorities and the majorities of onboard medical volunteers are not pediatricians.
For domestic air travel there is no requirement for certification of vaccination, however, for international travel the ‘International Certificate of Vaccination’ (PHS-731) is required. The immunization require-ments vary somewhat according to the health requirements of the country of destination. Travelers, who do not possess the required proof of vaccination, may be subjected to vaccination, medical follow-up, and/or isolation. In some countries, the unvaccinated travelers are denied entry. Nevertheless, majority of countries do not require the certificate for infants less than 6 months or 1 year of age. When a physician thinks that a particular vaccination should not be performed for medical reasons, the sick traveler should be given a signed and dated statement of the reasons on the physician’s letterhead stationary(4). The person authorized to sign the ‘International Certification of Vaccination’ has to be a licensed physician. Yellow fever vaccination is available only at sanitary airports, and needs to be taken at least 10 days in advance. There are no other acceptable reasons for exemption from vaccination. The medical officer at sanitary airport is the final approving body. Small pox vaccination is no longer a requirement for international air travellers.
Several international and some domestic airports have special facilities for the children. The designated ‘Mother’s Rooms’ are meant for interim care of the babies, where they can be given a change and feed. Some of the airports maintain a well-staffed nursery where older children can be left for short periods, or entertained during periods of long awaiting, such as between connecting flights or in the event of delays in flight. London’s Heathrow airport has a trained nurse on duty in its nursery area, where children up to eight years can be looked after. Frankfurt Airport nursery can handle more than 100 children a day. On prior intimation, the children are provided special children food in the waiting area and onboard aircraft, while being supervised by escort/cabin crew. The special ‘patient’s diet’ in case of diabetics and other metabolic disorders is not always possible onboard. Usually, the in-flight supervision is free of charge, except for ‘child escort’ services. The cabin crews are essentially trained in first aid(5). For specialized inflight medical care and safer outcome, a medical doctor/pediatrician preferably conversant with basic aviation medicine must accompany. The international flights could last up to 18 flying hours with short hauls in-between, depending upon the destination chosen for specialized treatment. Pre and post flight delays due to immigration, police verification, health, baggage, customs, etc. may take long time, anywhere between 30 minutes to one hour, besides additional waiting periods for connecting flights, if any. The medical atten-dant must plan well in advance for these delays. In the event of need, he may inform the airline/airport health authorities immediately or seek airline help for early clearance, help of airport doctor or an ambulance both at the airports of arrival and destination. At well-equipped airports, an early disembarkation is facilitated by use of ‘High Lift’ ambulance, which can collect the sick, bypassing the conventional aero-bridges and escalators. However, this facility should be utilized exclusively in an emergency and for severely handicapped patient.
WHO considers a premature baby as the live born infant delivered before 37 weeks from the first day of the last menstrual period(6). Information on the exact age of the baby is usually volunteered by the escort/attending physician on his own to the airline medical authorities. The premature neonates are at high risk of hypothermia, hypoglycemia, volume depletion, respiratory distress and cardio-vascular decompensation, sometimes manifest-ing at ground level itself. The thermal enviornment in the aircraft gets cooler at the altitudes due to falling ambient temperatures as well as cabin air-conditioning factors. Low temperatures may impose a significant stress and discomfort in unpressurized helicopters and aircraft. Under these situations, an adequate protection is required, as the premature neonate tends to lose heat more rapidly than term neonate does. The reasons are exposure of its relatively large body surface area compared to the weight, poor thermal regulatory mechanisms, low subcutaneous fat and inability to shiver. The environment at high cabin altitudes is low in moisture, with relative humidity as low as 10% and hence the exposed skin and conjunctivae need active protection. The use of skin hydronourishers like ‘Emolene’, moist towels available on board and tear substitutes such as ‘Aqua Tear’ are beneficial. An effective air transfer with in-flight facilities close to hospital neonatal intensive care unit (NICU) conditions may be feasible exclusively in highly specialized large air ambulances. The same is usually not possible in a small-bodied commercial aircraft. Specialized feeding arrangements suited to particular sickness are to be made by the escort/attending physician considering the duration of the flight. Caution may be exercised with tube feeding, as it is likely to induce bloating, diarrhea and infection.
Extreme hypoxia has often been associated with fetal loss. However, in commercial aircraft the environmental stresses are not considered hazardous to this an extent for the fetus of healthy mother. The latter is likely to have about 90% hemoglobin oxygen saturation at cabin altitudes of 5000-8000 ft. The fetus is well protected due to the peculiarities of fetal hemoglobin (Hb F) and its oxyhemoglobin dissociation curve (ODC). The ‘Bohr effect’ in the HbF remains nearly unchanged under these conditions(3). On exposure to decreased partial pressure of oxygen, the oxygen saturation of HbF in fetus drops less precipitously than that of the mother(7). Studies at 32-38 gestational weeks have not shown any acquired differences in fetal heart kinetics including beat to beat variability and brady or tachycardia irrespective to the cardiac status of the mother(8). The primary concern to the fetus is not only from the fetal distress, but also from other potential risks of certain aviation stressors on the mother. These include effects of gaseous expansion in the body cavities of the mother, effects of vibration and turbulence, use of restraint system on pregnancy, leading to higher risk of preterm delivery. Hence, most of the air carriers allow the pregnant mothers to fly maximum up to 36 weeks only. Routinely, about 92-94% pregnan-cies are known to enter into spontaneous deliveries after 37 weeks of gestation(9). The onset of labor is difficult to predict even when there are no overt indications of impending labor. Caution may be exercised as many women choose to ignore these risks and continue flying by giving false information. The medical advisors are required to be fully conversant with medical rationale and not get taken in by customary practices or the recommendations of non-medical bodies. While an early medical relief may be possible on short duration domestic flights, on an international flight the same may call for a very expensive diversion of the aircraft at unforeseen locations.
Congenital heart diseases (CHD) affect 9 per 1000 children, over one half of which require medical intervention(10). The incidence of CHD is high in low birth weight babies Lowered barometric pressure at increasing altitudes causes corresponding fall in the partial pressure of oxygen PO2. It results in decreased combination of oxygen with available blood hemoglobin, and cause ‘hypobaric hypoxia’ which remains a major concern in the acceptance of children with CHD, the ones already having circulatory compromises incurring ‘hypokinetic hypoxia’. Normally, the Alveolar PAO2 is 103 mm Hg. CHD with abnormal shunts between the right and the left side of heart diverts a portion of venous blood reaching the arterial side, without passing through the lungs and thus add to hypobaric hypoxia. Consequently, the arterial blood accumulates still higher fraction of deoxygenated blood under additionally imposed altitude hypoxia. The commercial airliners’ cabin altitude of 8000 ft correlates with an atmospheric pressure of 565 mm of Hg and atmospheric oxygen of 118 mmHg (21%). At this cabin altitude in healthy individuals, an arterial PO2 of 65 mmHg is achievable with inspired PIO2 of 108 mm Hg, compared to PO2 of 98 mm Hg at sea level pressure(11). The normal blood oxygen saturation at about 93% is acceptable at 8000 ft cabin altitude. The cardiac patient attempts to compensate altitude hypoxia to a certain extent through various physiological compensatory responses to hypoxia, within his compromised cardiac status. These include increase in depth and rate of respiration, heart rate, systolic blood pressure, rate of circulation and cardiac output. The tachycardia, in turn tends to worsen the condition due to an increased cardiac demand of oxygen. Thus, combined with aviation stress of hypoxia, a pre-existing CHD may aggravate inflight with an increase in symptomatology and cardiac decompensation despite satis-factory pre-flight status. Consequently, the use of medical oxygen may be required as continuous administration of 100% O2 or as standby during air travel. Acyanotic congenital heart diseases unless symptomatic, or complicated by respiratory infection, do not pose much risk to altitude hypoxia as well as to other aviation stresses including mild hydrostatic shift of blood in capacitance vessels under low ‘G’ acceleration and prolonged sitting environment of civil airliners. Cyanotic CHD, on the other hand, tend to deteriorate rapidly unless supplemental oxygen is given and the cardiac status maintained continuously in stable state.
Severely decompensated case of congestive heart failure (CHF) is a contraindication to air travel in any age group. Degree of cyanosis may not be a good parameter for assessing fitness for air travel. Infants having PaO2<60 mmHg with normal or low PaCO2 should be put on 100% oxygen during air transfer. Infants with elevated PaCO2 at best should avoid air transfer till improved. Children with clinical stability and preflight functional New York Heart Association (NYHA) class III-IV status may travel with supplemental medical oxygen. Class III NYHA status under functional and therapeutic classification manifest marked limitation of physical activity, comfortable at rest, but having less than ordinary activity causing fatigue, palpitation, dyspnea, or anginal pain. Class IV status is known to exist when the sick are unable to carry out any physical activity without discomfort. In these cases, the symptoms of cardiac insufficiency or of the anginal syndrome may manifest at the rest itself. Thus, if any activity is undertaken, their discomfort is increased(12). Additional aviation and physiological stresses may be disastrous, unless minimized. Such cases require thorough evaluation and close monitoring as to ensure safety during air transfer.
Symptomatic valvular heart disease is a relative contraindication to air travel(3). Preflight clinical assessment of the affected child must be done to assess functional status of the heart. Left ventricular dysfunction and pulmonary hypertension are critical criteria for non-acceptance. Inflight use of supplemental medical oxygen is recommended in case there is pre-existing baseline hypoxia due to any cardiac abnormality, including arterio-venous shunts.
Severe cases of anemia of any etiology, in particular sickle cell anemia and that secondary to leukemias are usually not accepted on account of greatly reduced oxygen carrying capacity of the blood. At normal arterial PO2 of 95 mm of Hg, the hemoglobin is only about 95-97% saturated while its combined oxygen content is 19-vol % in arterial blood. Arterial O2 content varies with hemoglobin content of the blood. Therefore, whenever the hemoglobin content of blood is reduced, its O2 content is also reduced proportionate to the degree of anemia. Under the circumstances, the altitude hypoxia only compounds the patients’ preexisting anemic hypoxia. Consequently, in apparently stable case at ground level, the overt signs of decompensation may appear as the patient reaches certain altitudes with hypoxic stress. In such an eventuality, medical oxygen should be used in order to prevent complica-tions. Slightly anemic patient may be trans-ported by air without much difficulty, as anemic hypoxia is quite small. For an air traveler both in health and disease, the hemoglobin levels of 10 g/dl are usually acceptable minimum without the use of supplemental oxygen(3). For the sick, however, the minimum acceptable level of hemoglobin is 7.5 g/dl; nevertheless, whenever they need to fly, they have to be on supplemental oxygen. All cases having lower hemoglobin than this level are to be put on transfusion in case an immediate air evacuation is required. In planned evacuation without constraints of time, the case may be put on appropriate hematopoietic therapy as to raise hemoglobin levels to the desired minimum. Asymptomatic children with sickle cell trait may take to flying in usual manner, since the concentration of HbS in their blood is usually less than 40% which does not permit sickling to occur at physiological oxygen tensions(13). While the known cases of sickle cell disease should be put on supplemental oxygen especially in unpressurized aircraft, in severely symptomatic patients oral administration of hydroxyurea helps in reducing the painful crisis and acute-chest syndrome.
An aircraft may be exposed to various degrees of air turbulence during its flight. One may experience vibrations and occasional buffeting. Consequently, a patient under air transfer requires proper restraint for in-flight monitoring and parentral medication besides safe transfer including safety in event of crash/crash landing. Depending upon distribution of forces, the impact forces may impose low to high life-threatening decelerative injuries, affecting his soft tissues as well as the bony organs. Rare incidents have occurred wherein with sudden loss in height such as on inadvertent tripping of the autopilot, the inertial forces had resulted in serious inflight injuries requiring subsequent hospitalization of the infant. The spacious adult size seats are inappropriate for children. They threat serious risks when an adult two point restraint is applied onto much smaller infant or young child. At present there is a move to introduce infant seats in commercial airplanes by law in US(14) although, there are as yet no specifically designed safety seats in the aircraft for children. Consequently, as an interim measure, the automobile child seats are considered to provide good protection and carriage for sitting sick as well as healthy small children in the aircraft, and are recommended(14). By and large, these are add-on products and their safety claims have not been well-substantiated(15). In India, commercially there are two different types of automobile baby seats available. One of them is ‘hang on’ type with fixed semicircular restraint in front. It hangs loosely on to the seat back. Such a seat is unsafe in aviation environment due to its possible displacement under turbulence. Another type ‘strap on seat’ is safer, however its attachment with passenger seat needs lot more care for proper anchorage as the aviation seat has no slots for the same. It has shoulder-crotch (y) type 5-point strap harness with three adjuster locks. The American Academy of Pediatrics has recommended safe practices for automobile transportation of premature infants, which have been updated recently in 1996(15). The ergonomics of electronically activated aviation passenger seat and its manual restraint systems are quite different from fixed backseats available in conventional automobiles, usually without any integral harness system. Its safety gets threatened when the child is himself able to activate electronic seat controls mounted on hand rest. The Aviation class seats have metal armrests with seat width 18.5 to 20.5 inches (47-52 cm) and is able to recline from 7 to 34 degrees additonally. Therefore, any of these seats would need careful risk free anchorage to suit the situation and restraints needs of sick child. Orthopedically restrained children and those requiring special inflight medical care may need full seat/s to themselves. A stabilized lap passenger may not require elaborate arrangements. On prior request, airline may provide bassinet for infants and children below two years exclusively for the front row occupants. Most safety seats for small infants are intended to place the infant in the rear facing position by design, which as well facilitates enhanced safety, clinical observation and the treatment. For the infants and children who are too young (under 9.1 kg) or incapa-citated to sit up, a recumbent restraint could be used(16). The small children weighing between 9.1 to 18.1 kg are usually able to sit up. For them, the child seat should be installed in a seat located in the rear of the airplane, a little away from an entry or emergency exit door. The installation is to be followed in accordance with the instructions on the seat and should be secured additionally by the aircraft seat belt. When the children overgrow the safety seat, they can safely get in the seat by using only the airplane seat belt. Larger children can use shoulder harness as well, if it does not rub against face and neck in seated position. Standard aero-stretcher may be used for larger lying sick children, at the cost of three passen-ger seats. It is very important to understand that when the restraints are improperly installed, they could be harmful and cause injury.
The use of onboard oxygen as ‘scheduled’ and ‘nonscheduled’ requirement has increased significantly over past few years. A survey amongst three major airlines, viz., British Airways, US Air and Quanta’s indicated that 1504, 3817 and 217 passengers requested for scheduled use of oxygen in the year 1992, when 26, 55 and 3 million passengers travelled these airlines(17). However, the actual number of passengers using onboard oxygen was still higher, as 2124 and 1000 passengers in just former two airlines used unscheduled oxygen. Majority of the users suffered from chronic respiratory disorders. In the second group Asthma remained the single most common respiratory disorder for which therapeutic oxygen was requested. The children may respond differently in close and low humidity recycled environment of the aircraft. Most children prone to hypoxia may be transfered safely when they are in pre-flight stable state, provided standby oxygen is available for in-flight demand or continuous inhalation. To determine the necessity of inflight supplemental oxygen for high-risk infants (Table I), a preflight evaluation test with 15% oxygen may be administered to all the infants having PaO2 less than 80 mm Hg with normal or low PaCO2. Infants with arterial PaO2 less than 60 mm Hg would require supplemental oxygen. When the arterial PaCO2 is high, air transfer must be delayed till desirable stabilization on ground is achieved.
Commercial airliners have two types of oxygen systems available to the passengers. These include the ‘fixed’ and ‘portable’ breathing units. The fixed systems derive their oxygen supply from large oxygen cylinders with large capacities ranging from 1100 to 3200 liters charged to 127 bars (1850 PSI) stored in the aircraft through aircraft ‘oxygen ring main’, constituting an integrated aircraft supply system(18). It supplies oxygen to the passengers and the cabin attendants. The oxygen concentrators are usually not available for passengers on airliners for power supply and other operational reasons, with exception of some dedicated flying hospitals. Upon activation of the altimetric switch (such as during decompression), the latch in the over head panel releases the door, which opens up allowing the passenger oxygen mask fall down in front of the passenger. Each passenger mask drop out module has design option to contain between one to five passenger masks. By pulling the mask down, the manifold pin in case of gaseous supply or generator striker in case of chemical oxygen supply, releases the oxygen flow to the passenger. These masks have a ‘rebreathable economizer bag’ as well as a ‘flow indicator’. The portable units are used by aircrews in the following circumstances: protection against fire, smoke or toxic gases, respiratory aid in case of depressurization, while permitting movements within the aircraft cabin and therapeutic treatment to sick passengers. Two types of portable oxygen cylinders are available to the users: ‘steel cylinders’ in conformity with US regulations (DOT-1800-3AA) and the light ‘alloy cylinders’. Capacity range from 120 to 310 liters of oxygen gas (NTPD) in three versions (GAF, steel) painted green, and 2 versions (GLF, light) painted white. They have two position valves and universal ISO standard coupling, that allow connection for a passenger range of masks, anti-smoke masks, even pilot emergency masks requiring flow rates as high as 200 L/min. Unlike aircrew protection mask, e.g., MW-37 series, the therapeutic masks are of disposable type. They exist in adult version (Mk-10) and child version (Mk-5) and meet the FAR regulations requiring the possibility of providing oxygen flow rates of 2 or 4 I/min from the two position manual control selector (DMZ 20) provided on the oxygen cylinders. Higher flow rates cannot be provided through aircraft oxygen systems for the passengers. Under normal circumstances, the passengers and their supporting hospitals cannot provide certified airworthy oxygen apparatus for onboard use. Other than a few national air carriers, airlines generally charge for scheduled oxygen(19). Some sick children may require ‘bag valve mask’ ventilation. A prior informa-tion to the concerned airline is necessary for making suitable arrangements. Table I - Decision Making on Air Transfer of High Risk Infants with Cardiopulmonary Lesions
The availability of oxygen varies with the origin and design of the helicopter. Currently, the helicopter operators in India have Bell- Longranger, Eurocopter- 135, Mi-8, Mi-172 class of helicopters. Pawan Hans, the country’s largest helicopter operator has some 30 helicopters. In one of the commuter helicopter of Mi-8 class, two or three 7.6 L oxygen bottles are available(20). These have an average endurance of 30-45 minutes and require O2 bottle replacement every time a little before the exhaustion of the gas. The oxygen is available to adults through ‘KM-15’ mask of continuous flow type. It can be easily replaced by pediatric bag valve mask. The O2 bottles are charged to a pressure of 30 kg/cm2. Helicopters of French origin have ‘EROS’ oxygen system. For any oxygen system in use, it is advisable not to deplete the oxygen bottle completely as it encourages corrosion within the bottle. Conventional precautions, viz., prohibition of smoking, proximity of mineral based oils and sparking from medical equipment especially suction pump or a naked flame are essential safety measures.
A ‘bag-valve-mask’ (BVM) ventilation device is ideal for the ventilation of this group Pediatric BVM’s should not contain valves that get occluded easily, as the required ventilation pressurs may exceed the limit of ‘pop off valves’. Demand valves should not be used for pediatric resuscitation. At the lower tempera-tures of cabin, it is rather difficult to maintain the desirable relative humidity of 40-60%. The benefits of continued oxygen administration must be weighed against the potential risk of retinopathy, i.e., retrolental fibroplasia in premature neonates. Administration of oxygen through endotracheal or nasotracheal intubation may cause irritation of respiratory passages due to dryness. Respiratory functional status can be monitored with use of autonomous pulse oxymeter.
In an event of sudden unforeseen onboard emergency requiring use of ‘Oxygen Tent’, an improvised version can be innovated by using any ‘life jacket bag’ large enough to cover the head of the child. Oxygen can then be supplied by inserting the oxygen tube after removing its mask. The other end of the tube is connected to the oxygen bottle outlet. In case of an infant, it is advisable to place him in an upright position with enough space available between the face and the bag. Electrically operated ‘Oxygen Tents’ are not permitted by most of the airlines due to technical reasons. Some dedicated air ambulances may support ‘Oxygen Tents’ in special cases.
Transfer of sick children in emergencies in an air ambulance or commercial airplane, may require advanced in-flight physiological monitoring systems that are usually required in any modern pediatric ICU or a perinatal unit. Such equipment may include sphygmomano-metery, EKG monitoring and pulse oxymetry besides routine and basic clinical monitoring. Their importance becomes especially high in critically sick transfer flights lasting for over half an hour or so. The electricity available in the aircraft is not compatible with most of medical monitoring systems that we commonly use in ground based hospital scenario. It is because the aircraft systems work on different, 28 Volts electric supply. By conventional stethoscopes substantial difficulties are experienced in auscultation of breath and heart sounds and manual monitoring of blood pressure in cabin environment because the passenger cabins of majority of aircraft have relatively high levels of background noise. The latter could be as high as 82-95 dB(21). Consequently, the conventional stethoscope proves virtually useless in aviation environ-ment. Therefore, ‘Doppler techniques’ and/or ‘electronic stethoscope’ is recommended for use in cabin environment. Currently available electronic stethoscopes combine the familiar acoustic stethoscope with microelectronic technology and offer amplification up to 14 times in 8-level volume control selections. Their greatest clinical advantage is in the filtration of the ambient noise and the induced noise due to hand tremors of the observer. The later facilitates auscultation of breath sounds in an event of endotracheal intubation as well. The voltage rating of typical ‘portable noninvasive blood pressure monitor’ is 115 V AC 60Hz, current 400 mA, and 45 watts. The battery voltage rating is 12 Volts DC with limited usage time. In not very old machines, the charge time may take about 2 hours or more following each hour of operation. The newly introduced portable equipment operates on longer lasting cell batteries with endurance of 24+ hours of monitoring.
A child subjected to ‘Air-Cas-Evac’ may need onboard monitoring of oxygen hemo-globin saturation (SaO2) using pulse oxymeter. It may have to be modified to run up to 10 hours or more on external batteries depending upon the total requirements of air travel. As discussed earlier, the aircraft electrical system is not compatible on account of differences in operating voltages and frequency factors. Typical power rating of portable oxymeter is 110 or 220 V, 50/60 Hz, 12 W maximum. It may be operated on rechargeable Nicad 4.8 V DC, 1.8 Amp hours and its usage could be extended up to 8+ hours, after which it would require a replacement or recharging. The latter cannot be done in the aircraft, but may be carried out at intermediate halts. A special electrical interface ‘Medical Inverter’ is not routinely available on commercial airliners. Before the acceptance of any supportive electric/electronic equipment by airline for onboard use, the airline technical authorities have to clear it for possible sparking, electro-magnetic emissions, which may interfere with aircraft communication and avionics. In grown up children, the ear probe method is more convenient to use onboard than finger probe method. Oxymeters with digital storage of data at intervals can help in retrieval of information with detailed analysis on subsequent hooking on to a laptop or desktop computer. The use of laptop computer is not permitted to be used during landing or take off phases of the flight. Variance of 3-4% in SaO2, especially after meals are considered of no consequence. At 8000-ft cabin altitude, the anticipated oxygen saturation levels in otherwise healthy indivi-duals are likely to range from 91-80%.
Cases requiring ‘Incubator’ are usually not accepted for air travel on commercial aircraft; however, they are occasionally permitted onboard certain dedicated air ambulances. These are operated through specialized medical plugs, available with ‘medical inverter system’. These may be affixed at a predetermined place in the cabin on demand, more liberally in some of the modern and wide-bodied aircraft. These plugs are not at all available on B-727 and older class of aircraft. Besides many supportive problems, the incubators are known to generate about 72-74 dBA noise in hospital nursery itself. In aircraft cabins, the ambient noise levels may range from 70-90 dB, and be still higher in the cabins of helicopters. Under usual ground nursery conditions, the inside environment of incubator is known to pick up human speech outside the incubator in muffled and indistinct form. In one of the in-flight studies, the noise levels in the incubator were found to get further amplified by 5dB. Thus, under actual condi-tions of the helicopter environment, the noise level were found to be as high as 93-99dBA in the incubator(21). The overall sound levels in the incubator further tend to vary with use of fan, heater, oxygen equipment, etc. Noise and vibrations are known to affect some sick neonates and infants rather adversely, especially those with convulsive disorders. The British safety standards specify the limits of mean noise levels inside the incubator as 60-dBA, which is equivalent to noise levels during normal conversation(22). The high ambient noise levels in pressurized as well as unpressurized aircraft cabins may also interfere with incubator alarm recorder usually set to a noise level of 85-dBA. Noise is known to result in physiological and behavioral disturbances in young ones, induces motor arousal such as startle and crying and may precipitate undesirable hypoxia, tachycardia and increased intracranial pressure(11,21).
This requires special care during air transfer of children. Numerous difficulties may be experienced by the medical attendant on account of undesirable movements of the child, aircraft turbulence and vibration, low visibility due to poor illumination levels inside the cabin, lack of securing points for medical equipment, lack of space and unsuitable platform for intravenous (IV) insertion with several other compounding factors. Therefore, the intra-venous cannulation/catheterization should be carried out on the ground itself, well before boarding. The child must be watched for sometime as to ensure proper placement and patency of the drip. Due to expansion of gases within the IV bottle at altitude, the rate of flow of the fluid is likely to vary significantly thus altering the rate of drops/min. The attending physician must be careful of the rate at which the drug is being administered. The consulting pediatrician must also consider such in-flight factors before planning any drug administration through IV fluids during air transfer.
Expansion of Air in Body Cavities Some of the usual concerns affecting adult population, viz., those arising out of air expansion in closed cavities of the body with increase in cabin altitude are of lesser significance in babies and young children. The decreased density of air to half at 18,000 feet altitude and one third at 25,000 ft results in proportionate expansion of gases. However, it does not significantly reduce the turbulent flow in the airways to the extent of increasing maximum expiratory flow rates in healthy or the individuals with COPD(23). It is because, unlike the military aircraft and other small transport aircraft, the cabin environment of the airline is not subjected to rapid ascent or descent, as the incurred variation in pressure lies only between the ground level atmosphere and the cabin altitude. The maximum rates of change in cabin pressures approximate 500-ft/min in increasing altitude and 300 ft/min in decreasing altitude, and therefore they do not pose any problem to typical passenger(24). Thus, the current pressurization criteria in civil airliners are generally more than adequate to protect the travelling passengers and crew. Ear Pain in Children During Air Flights The pressure changes in commercial airlines are less likely to cause aero-otitis media. It is because the Eustachian tubes of infants and children are relatively straight anatomically, thereby facilitating the equalization of pressure across the tympanic membranes of the ears without serious consequences. The high elasticity of the tympanic membrane in children can withstand higher-pressure differentials of 107 mm Hg across, in comparison to an adult tympanic membrane, which is at risk of damage at pressure-differential of 85-90 mmHg across the tympanic membrane(11,24). This naturally protective factor helps greatly under conditions of sedation and unconsciousness due to any reason. In children with nasal block due to upper respiratory tract infection, allergic predisposition of nasal mucous membrane, decongestant nasal drops should be adminis-tered at least 15-30 minutes before descent is commenced. Children with acute salpingitis of Eustachian tube, chronic salpingitis, abnormal patency due to congenital and other reasons including patulous Eustachian tube are at higher risk of barotitis media. In one of the studies, the rate of ear pain during take off was found to be about 5% in children(25). The ear pain rates during descent were 8% higher than those observed during landing. The administration of pseudoepherine nasal drops was found to alter these rates only marginally. Swallowing, yawning and jaw opening/gaping movements are helpful due to muscular action on the walls of Eustachian tubes that usually open up the internal auditory tube. It is a good practice to give some chocolates to children during descent to prevent ear pain and barotitis. Keeping the children awake during landing and take off is advisable, as active swallowing for any reason would decrease the incidence of ear pain. Post flight inflation of the ears further helps in the relief of symptoms and prevents delayed otitic barotrauma(26). Expansion of Air in Body Cavities–Local and Systemic Effects Crying and suckling helps positively by similar activation of the tubal muscles. How-ever, it may precipitate aerophagy, which in turn can result in abdominal discomfort at increasing cabin altitudes due to further accumulation and expansion of trapped gases within abdomen. Burping the child with effective expulsion of the trapped gases in the gastro-intestinal system is the best help in relieving the situation. Loose clothing remains preferred choice for air traveler and evacuation of sick. Expansion of gas remains a major concern during parenteral administration of fluids, recent surgery, air embolism, cavitating teeth, cavitating lesions in lung parenchyma and other tissues, parenchymatous bullae, etc. during air evacuation. Aero-dontalgia may be experienced in travelers with recently filled cavities in teeth. Overlooked loculated air pockets in brain after cranial injury or surgery could be disastrous. Inflatable splints should be avoided during carriage of fracture cases by air; else the expanded air within the splint may cause severe restriction of circulation. A cabin altitude of 5,000 ft would give an expansion of air in volume by 1.2 times.
The relative humidity in the aircraft at altitudes range from 5% to 35% with an average of 15-20% (US DOT sponsored study 1989). The overall humidity in cabin environment depends upon the number of passengers leaving moisture in their expired air. It however decreases with inflow of the fresh air in the cabin. Some passengers do feel uncomfortable after exposure to three or four hours of low relative humidity cabin atmosphere of 5-10% range(22). The discomfort could manifest as dryness of the eyes; irritation of nose and throat especially in those patients/passengers put on 100% dry oxygen inhalation. However, it does not lead to any increased risk of serious difficulties or health effects in flying population likely to be travelling only for few hours. Dryness of the eyes may increase with the use of antihistamines. Sick in comatose conditions may need ‘artificial tear’ as moisturizing agents.
Diabetes in childhood is uncommon in infants and toddlers. It increases in frequency until adolescence and thereafter declines sharply(27). By about 18 months of age, the peak incidence falls earlier in girls than boys. A recent study suggests an incidence of 10.5/100000/year in population of children in India(28). Any patient, with any type of manifest diabetes mellitus doing air travel on long transmeridian flights should remain on home time for the purposes of medication and food intake thoughout the flight. Airline may be requested to arrange special diet for such passengers. The medication must be carried in the hand baggage, as it is not possible to take it out from cargo hold of the aircraft, once the aircraft is airborne. After reaching the destination, further adjustment of treatment to the new time schedule coinciding with local time should preferably be done under medical supervision.
As per existing policies, HIV infection and AIDS are no contra-indication to air travel(29). On international flights, their acceptance is guided by the immigration and health laws of destined country, and can be referred from ‘CDC Health Information for International Travel’ yearly updates(4). Proper care of their bio-wastes, bio-fluids and bio-spills must be done with suitable gloves, waste bags and containers. Screening for pulmonary cavitating lesions must be done to exclude their open and infective nature, and to ensure safe air travel.
Medical documentation makes a very important part of successful air transfer. The escorting doctor must ensure collection of all relevant medical documents including laboratory investigations reports and endorse all medication rendered during transfer with their dosage. The attending physician is also required to fill up necessary performa in case he has used any of the contents of onboard medical kits for perusal and replacement by the medical department of airline. During inter-national transfers, medical documents assume still greater importance for smooth handing over, acceptance at various levels including immigration, customs, airport health depart-ment and further treatment.
It constitutes an embarrassing situation for the attendant, the co-passengers, the airline as well as the authorities at the destination airport. Due to good and responsible self-reported screening, the incidences of onboard deaths have been rather low. Out of the total passengers of 30 million carried during 1994 by various airlines, only 25 deaths were reported(30). Children are usually more prone to sustain onboard injuries due to various ergonomic factors, especially during violent maneuvers of the aircraft or sudden decelerative forces. Sick children are always at an additional risk. Both the conditions may invite medico-legal implications. These are guided by local rules at the country of destination. The attending/escorting physician needs to be conversant with relevant laws.
For majority of the normal children, air travel is unlikely to be harmful in its outcome during the flight or post-flight. Nevertheless, most of the airlines decline the request to carry the following sick children.
The usual absolute and relative contra-indications for air travel are summarized in Tables II-IV. Table II - Contraindications to Air Transfer
Table III - Relative Contraindications
Table IV - Relative Contraindications-Do’s and Don’t’s
Air transfer of sick children is a highly specialized task imposing challenges on experience, skill, and knowledge of escort/attending physician in basic aviation medicine and carriage of airworthy medical equipment for effective in-flight use. Medical handling of the sick on ground is not exactly identical to that in air due to aviation related physical, physiological and psychological factors. Proper awareness towards aviation stresses and their possible impact on the sick as well as treatment modalities are a must for treating physician involved in air evacuation of the sick. Unfortunately, at present no formal training is being given to the dealing pediatricians and clinicians despite the fact that air transfer of sick is fast becoming one of the most accepted and critical time saving mode of evacuation. Irrespective of formally imparted training, the attending/consulting clinician remains the sole responsible person for any mishap during such transfers. It is therefore mandatory, that a careful thought be given towards underlying patho-physiology of the disease condition, the physical and clinical status of the patient, the medical support required at boarding as well as destination ends and the in-flight care for the entire duration of the flight. With prevention as the best alternative to unpredictable inflight interventions in restricted places, availability of limited equipment and in altered environ-ment of aviation, the certifying doctor must be cautious as to prevent any occurrence of regrettable outcome in the air. Contributors: NNA drafted the paper and will act as the guarantor. SA shared personnel experiences and implications in casualty air evacuation of the sick children and helped in drafting.
Funding:
None.
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