By Mark A. Merlin, DO, EMT-P, FACEP, Joshua Schwarzbaum, MD, EMT, Sim Shain, MICP, EMT-P, NRP, Mark Chapman, RN, Ammundeep Tagore, MD, MSHA, MBA, Navin Ariyaprakai, MD, EMT-P, FAEMS, Jodi Pritchard, RN, BSN, CCRN, CFRN, Joseph E. DiCorpo, BSC, MMSc, PA and Alexander Torres, DO, MBA | 3.6.19
The need to move ill or injured patients from one location to another by air isn’t a new concept. Injured soldiers were among the first patients in history to be transported by air to a medical facility, beginning with the use of hot air balloons in 1784.1
Since fixed-wing aircraft were developed in 1903, the use of these engineering marvels for patient transport has seen incredible advances.
Although an invaluable resource, in addition to the medical care required on the ground, there are important physiologic changes that occur at higher altitudes and must be considered by the transport personnel.
Some of the physiologic changes include, but aren’t limited to, development of hypoxia, potential for gas expansion, and effects of gravitational forces. These impacts on patient homeostasis must be addressed prior to patient movement to ensure patient safety and provide for the best patient outcomes.
The goal of this in-depth article is to educate clinicians on factors that must be addressed prior to, and during, the fixed-wing air medical transport of a patient.
Patients with critical illness are at increased risk of morbidity and mortality when exposed to the stresses of air medical transport.2 Mayer reports that “between 24 and 70% of transferred patients are inadequately stabilized prior to and during transfer.”3 Therefore, appropriate pre-flight patient preparation is imperative to patient safety and successful patient transport.
The origins of air medical transport date back to the late 18th century, where hot air balloons were considered to move patients off the battlefield.1 This method of patient transport didn’t see success for nearly 90 years. The first report of successful air transport of patients comes from the Siege of Paris in 1870, where patients were transported from the battlefield to hospitals via hot air balloons.4
The Wright Brothers’ development of the first successful fixed-wing airplane in 1903 opened the door for significant progress in air medical transport. Less than 15 years after that first flight, in 1917, the first successful fixed-wing patient transport was conducted in Turkey using a French Dorand AR 2 aircraft.5 The following year, two U.S. Army officers converted a Curtiss JN-4 biplane into an air ambulance.4
Following World War I, there was additional development of air ambulance services, and in 1928, the Royal Flying Doctor Service was established in Queensland, Australia.4
Continuing advances in military aviation allowed for dedicated air medical evacuation units on fixed-wing aircraft in 1943.5
The United States saw the first U.S.-based, Federal Aviation Administration-certified, air ambulance established in Los Angeles, California, in 1947.4
The first half of the 20th century saw rapid development of air medical transport capabilities. Keeping with advances in military science, the U.S. Air Force piloted a team approach to critical care air transport in 1994 at the 59th Medical Wing at Lackland Air Force Base, calling it the critical care air transport team.6
As civilian air medical transport is increasingly utilized, it’s imperative to learn from previous experiences, both military and civilian, and improve processes, patient care and patient outcomes.
Knowledge of aerospace medicine and physics are vital information for air medical transport personnel. As reported by Teichman, Donchin and Kot, “keys to successful aeromedical evacuation are planning for and responding to any deterioration in the condition that mandated urgent transport and to conditions induced by the aerospace environment.”7
With regards to aerospace physiology, there are different physiologic zones of the atmosphere that become relevant. The efficient zone is defined as sea level to an altitude of 10,000 feet above sea level. In this zone, levels of oxygen are typically adequate to maintain baseline physiology without a strong need for supplemental oxygen or equipment.8
However, once entering the deficient zone of the atmosphere, 10,000 feet to 50,000 feet above sea level, there’s a decrease in barometric pressure as well as a decrease in the partial pressure of oxygen.8 The deficient zone is where the majority of fixed-wing flights occur and is also where physiologic issues arise during the air medical transport of patients.
To gain a better understanding of some issues that may arise during flight, understanding of Boyle’s law and Dalton’s law, at minimum, are necessary.
The most important physiologic consequence of flight is hypoxia. Dalton’s Law helps explain the mechanism behind in-flight hypoxia. Dalton’s law, PT = P1 + P2 + … + PN, states that “the total pressure of a mixture of gas is equal to the sum of the partial pressure of each gas in the mixture.”
By increasing altitude, the partial pressure of oxygen is decreased. To combat this effect, modern aircraft fly with pressurized cabins that are typically pressurized to an altitude of 8,000 feet.9
Patients with pre-transport hypoxia or respiratory compromise are likely to deteriorate in-flight if efforts aren’t made to optimize oxygenation throughout the duration of transfer.10 Boyle’s law, P1/P2 = V1/V2, explains that “the volume of a gas is inversely proportional to the pressure to which it is subjected.”
Based upon this law, pressure decreases with increased altitude, thereby causing an increase in the volume of the gas, leading to the concept of gas expansion. Some potential consequences of gas expansion/trapped gas include tension pneumothorax, dehiscence of surgical wounds (i.e., ruptures along a surgical incision), expansion of intracranial air leading to brain herniation, expansion of intestinal and gastric air causing a decrease in functional residual capacity of the lungs, thereby furthering hypoxia and respiratory compromise.7 To abate these consequences, efforts must be made to equalize the pressures. (See Table 1.)
Other physiologic considerations include low humidity, temperature changes and the effects of gravitational forces. (See Figure 1 and Table 2.) With regards to the low humidity of the aircraft cabin, patients will experience drying of secretions (eyes, nose, mouth, respiratory tract), dehydration, and increased mucous plugs.11
The risk of epistaxis (i.e., nosebleed) is also increased. Therefore, the crew should be prepared to manage this potential complication. Also, as altitude increases, the atmospheric temperature, in addition to humidity, decreases. Clinicians must recognize this effect and be prepared to warm patients as necessary.
Finally, gravitational forces experienced in acceleration and deceleration can impact physiologic processes. In critically ill patients, the effects of gravitational forces are exacerbated.11
In experiencing acceleration forces, patients may exhibit hypertension, dysrhythmias, shifts in compartmental fluids, tachycardia, increased intracranial pressure, decreased cerebral oxygen pressure and decreased venous return/cardiac output.9,11
Other, less commonly thought of issues with fixed-wing air medical transport are the effects of noise and vibration. This can cause pain, nausea and anxiety for the patient, and therefore should be recognized and treated as appropriate.12
When preparing to transport a patient via fixed-wing aircraft, there must be a significant amount of preparation. This should not be limited to preparation of the patient, but also should include preparation of all personnel involved.
A holistic approach to the patient transfer provides for the best possible outcome for the patient.10 Any time a patient is undergoing transfer, development and utilization of standardized procedures can help mitigate associated risks.13
To begin the process of preparation for transport, the historic “problem areas” need to be identified. Literature demonstrates that common areas needing improvement are communication, having the appropriate equipment, airway management, maintenance of IV lines, as well as education and experience of transport personnel.14,15
Communication errors can be devastating whenever they occur. When transporting a patient, it’s imperative that strong and effective communication tools are utilized. Some current communication errors that plague patient transfer today include inaccurate descriptions of patient condition and needs, miscommunication, lack of standardized resources available and poor utilization of such resources.14
It’s recommended that there be direct communication between transferring physicians and receiving physicians to ensure accuracy of clinical information.11,15
During the dialogue between physicians, the minimum information that should be relayed should include initial/presenting clinical condition, clinical course, present clinical condition, treatments given, current treatments, reason for transfer, recommended mode of transport, required transport equipment and medication, and recommended personnel required for transfer.11 Some ways to ensure adequate communication include the use of standardized tools, checklists, and to relay information in a structured manner.10,12
One tool that has been recommended to standardize the way patient information is communicated is iSoBAR (identify-situation-observations-background-agreed plan-read back).10,16 The components of this tool require that patient identity be confirmed and all relevant personnel introduce themselves to each other and the patient. The clinical situation, both recent and current, should also be stated.
Observations include recent vital signs, relevant laboratory data and critical medications. Background information should contain pertinent past medical history, family or social support, and any other pertinent patient information.
The plan agreed upon by the transferring and receiving physicians should be communicated clearly and a situational assessment and needs assessment should be performed. This should include anything that needs to happen prior to, during or after transport.
Once all of this information has been communicated, closed-loop communication should be performed by reading back the information that will provide clarity and confirm understanding.10,16 Ensuring good communication during all aspects of patient transport (before, during and after) will improve patient care and outcomes.
A topic that isn’t frequently discussed or researched is the correlation between patient acuity and potential for adverse events related to fixed-wing patient transport.17,18
The Acute Physiology and Chronic Health Evaluation (APACHE-II) system has been validated and used to classify severity of disease and to predict mortality in varied patient populations.18,19
Although the patient populations initially studied didn’t focus on patients that specifically required fixed-wing air transport, it can be hypothesized that patients with a higher severity score on APACHE-II scoring are likely to have higher mortality.
As patients undergoing fixed-wing air transport have added stressors to their already stressed physiologic processes, the severity of their illness should be assessed prior to transport.
A correlation has been demonstrated between APACHE-II scores and mortality, suggesting that the more critical a patient, the higher the mortality and likelihood of adverse events during transport.18
Some specific risk factors that can impact adverse events on fixed-wing transports include continuous cardioactive medications and the need for supplemental positive-pressure ventilation.17
Identifying these risk factors and using a standardized assessment of physiologic abnormalities can also help convey accurate patient information between medical teams.
As for the preparation of the patient for transport, we recommend an approach similar to the “primary survey” and “secondary survey” presented by the American College of Surgeons Committee on Trauma which recommends an ABCDE approach to the “primary survey.”
The components of the primary survey include airway, breathing, circulation, disability and exposure/environment. Following the assessment of these critical items, assessment should continue with a thorough head-to-toe physical examination to identify any other factors that may need to be addressed or stabilized prior to flight.
A critical step in patient transport is assessment and stabilization of the patient’s airway.2 If the patient isn’t already on mechanical ventilation, the transferring physician or flight personnel should evaluate the patient for signs of impending respiratory failure or airway compromise. If there is evidence of such, the patient should be electively intubated prior to transport.11
The ideal time for airway management is preflight. Once the airway is secured with either an endotracheal tube or laryngeal mask airway, the device should be secured using a tube holder. The size, depth and location of the tube should be documented prior to moving the patient.10,20
Controversy exists on whether the cuff of the tube should be filled with air or saline, however, it’s recommended to using an air-filled cuff as its pressure can be measured throughout flight using a manometer.10
The expansion of air, or fluid bubbles, can over-inflate the cuff and cause pressure necrosis or eventual strictures. When it’s been determined that the airway has been secured prior to transfer, personnel must keep in mind that the act of moving patients can cause equipment, including endotracheal tubes, to dislodge.5
Mechanically ventilated patients should be adequately sedated, receive pain control and receive neuromuscular blockade as necessary to maintain a secure airway.10,12
It’s asserted that hypoxia is the greatest threat to patient safety in air medical transports.1 This implies that breathing status should be optimized prior to transporting a patient.
This begins with trying to prevent hypoxia. Some potential prevention strategies include pressurizing the aircraft cabin, use low flight paths and provide the patient with a blood transfusion if preflight anemia exists.7
It’s the responsibility of the transporting personnel to anticipate oxygen needs during transport and ensure that the amount of available oxygen on the aircraft is adequate.10
Prior to moving the patient from the transferring hospital, the patient should be placed on the transport ventilator and be able to maintain adequate ventilation and oxygenation.15
If the patient can’t be stabilized on the transport ventilator, alternative equipment should be found or the transport should potentially be re-evaluated. In some situations, patients may require unusual ventilator settings not frequently used during transport, therefore, the patient should be stabilized on the transport ventilator prior to transfer and to ensure crew familiarity with the unconventional settings.2
Once the patient is stabilized for flight, continuous monitoring of ventilation and oxygenation should be performed by assessing the end-tidal carbon dioxide measurements and oxygen saturations.12
Also, in anticipation of potential ventilator malfunction, a bag-valve apparatus should be readily available.10 Physiologic responses to hypoxia include hyperventilation and increased cardiac output, which is usually manifested by tachycardia.5
Another factor that can affect breathing status is the presence or development of a pneumothorax. If there is a pneumothorax present prior to flight, it should be managed preflight with thoracostomy tube placement with a Heimlich valve, and tube placement should be confirmed.8,10
The tubing should remain unclamped, and transport personnel should have equipment available to perform emergent needle decompression in the event of malfunctioning thoracostomy tube or development of a pneumothorax in-flight.8
Also, for critically ill patients, a nasogastric or orogastric tube should be placed to prevent aspiration and to help with removing excess gas during flight.10–12
Continued discussion regarding breathing status and oxygenation must focus on the use of portable oxygen concentrators (POCs) during fixed-wing air medical transport. Historically, airlines provided, with advance notice, compressed gas oxygen cylinders, but this is generally not the case now for U.S. airlines.
Currently, the utilization of a battery-operated POC is common. This is authorized for U.S. airlines by the Federal Aviation Administration (FAA) and allows passengers to bring portable oxygen concentrators onto airplanes, as mentioned in the Code of Federal Regulations (CFR), specifically 14 CFR 11, 14 CFR 121, 14 CFR 125, 14 CFR 135, 14 CFR 1 and 14 CFR 382.
These regulations spell out the requirements for POCs and explain what air carriers may and may not require from passengers who need supplemental medical oxygen during all or part of their flights.
Rather than requiring the POC manufacturers to obtain FAA approval for each model of portable oxygen concentrator, the FAA now requires manufacturers to label new models of POCs that they comply with FAA requirements.
Older POC models that have already been approved by the FAA may still be used, even though they don’t bear a label. Airlines can use the list published in Special Federal Aviation Regulation (SFAR) 106 to determine whether or not the POC may be used during a flight.21
interchangeable battery, short- and long-life batteries, and a display that’s easy to use. Most airlines require you to have an adequate supply of batteries for 150% of the flight duration. The Inogen One G3 has both pulse (i.e., triggered by negative pressure coinciding with inspiration) and continuous oxygen administration. Continuous oxygen administration significantly decreases the battery life vs. pulse administration.
If you’re going to utilize one of these POCs for a commercial airline medical escort, you must do the following:
Addressing circulation can be a challenging task but is very important to patient stabilization. Regardless of the patient’s condition at time of transfer, at least one site of IV access should be established and maintained.2,10,12
For the more critical patients, two sites of IV access should be present. A patient’s fluid balance and intravascular volume can be difficult to assess without invasive monitoring, however, transferring physicians should aim to normalize the patient’s circulating volume prior to transport as hypovolemic patients tend to do poorly when moved.12
The preflight stabilization of fluid status is critical; but isn’t the end of fluid resuscitation. Due to significantly lower humidity at altitude, patients can become easily dehydrated throughout flight and experience insensible water losses.
This implies that volume replacement during flight is also an important factor in optimizing the patient’s condition. In addition to restoring volume with crystalloids, if volume loss is due to bleeding, volume should be restored via blood transfusion to maintain a minimum hemoglobin concentration of 7.0 g/dL.20
Additional blood for transfusion should also be taken on the flight with the patient in the event that in-flight transfusion is necessary. Increased altitude leads to lower barometric pressure, increased vascular permeability and dilated peripheral vasculature.9
This causes a fluid shift, commonly referred to as “third-spacing,” where fluids move from the intravascular space to extravascular spaces causing edema, dehydration and hypovolemia in-flight.11 A recommended way to monitor fluid status during flight is to monitor urine output via indwelling urinary catheter, which should be placed prior to patient transport.7,10,11,12
In addition to volume derangements, the actual flow of blood through the vascular system can be affected by air transport. Patients, as well as the crew at times, can be in an immobilized position for long periods of time, decreasing the normal flow of blood.
This venous stasis, part of Virchow’s triad, can lead to thrombus formation, and must be considered by flight personnel prior to transport.9,23
Concentrations of thrombin-antithrombin complexes have been identified as increasing after air travel, suggesting a potential mechanism for the increased risk of deep vein thrombosis associated with air travel.24
In patients that don’t have an existing thrombus, adequate hydration, use of compression stockings, and prophylactic use of anticoagulants should be considered.9 Not only should patients participate in prophylactic measures to prevent deep vein thrombosis, but crew members should also do so.
We recommend that crew members stay well hydrated and wear compression stockings/socks throughout the flight. Also, if in-flight conditions permit safe movement within the aircraft cabin, it is recommended that crew members ambulate at various intervals.
“Disability,” as it is referred in the primary trauma survey by the American College of Surgeons, focuses on the neurologic status of the patient. In flight medicine, it’s more commonly thought of as disturbed behavior.
Patients that are agitated, combative or disruptive can pose significant danger to themselves and flight crew members, therefore behavior disturbances must be addressed prior to transport.10
A potential cause for alteration in mentation is decreased cerebral oxygenation, which can be caused by patient positioning. Due to the acceleration forces, if a patient is placed in the head-front position for the flight, there will be blood pooling in the feet, potentially leading to decreased cerebral oxygenation.9
The control of pain, anxiety and delirium can be accomplished by using analgesics, anxiolytics and other medications as necessary. If a patient has previously been controlled on a medication prior to transport, reinstatement of such medication should be initiated. For patients that are mechanically ventilated, paralysis may also be needed, in addition to pain control and anxiolysis.10,12
An often-forgotten potential cause of agitation can be nicotine withdrawal, which may begin to manifest during flight. Addressing the patient’s nicotine status during the information gathering phase prior to flight can help determine whether nicotine withdrawal can become an issue.10
When the transport team arrives at the transferring facility to assess the patient, the flight team should expose and examine all areas of the patient’s body to perform a thorough assessment.12
In addition to exposing the patient to look for any other concerns that may not have been relayed to the transport team during verbal report, temperature control and other environmental factors must be considered and addressed.
Two important environmental concepts in flight medicine include decreased temperatures at high altitude and the lack of humidity leading to the drying of secretions.7,12
Patient temperature can be controlled using blankets, warm IV fluids and humidifying devices. The drying of secretions can cause dry lips and dry eyes, requiring lubricant medication to improve patient comfort.7 These medications aren’t considered critical or routine but shouldn’t be forgotten.
Once the ABCDE components have been considered and addressed, transport personnel should perform a head-to-toe patient assessment as well as a needs assessment. Look for evidence of potential trapped air in various body compartments, splints/casts, wired jaw, functioning equipment and any other items that may pose a hazard in flight.20
Some particular equipment needs that must be addressed are the availability of power sources, amount of batteries and their status, adequate amounts of available oxygen, and adequate amounts of available medication.2,7,12
Medication administration must also be evaluated. The flight crew must determine which medications are current and when the patient received the last dose. They must also be prepared to administer any timed medications prior to flight if they are due and should prepare, and begin, any antibiotics that are scheduled.15
Not only should the crew have enough medication for the flight, but in anticipation of any lost medication or flight delays, we recommend that a sufficient medication supply be available for at least 12–24 hours.
Other considerations when performing a fixed-wing patient transport include IV tubing, types of fluid containers, cast management, body cavity tubes and infection control. As Boyle’s law relates to gas expansion, any air trapped in IV tubing could expand and cause malfunctioning of the tubing and IV pumps, limiting the ability to provide IV fluids and medications.
Also, glass fluid bottles can break if air expands, therefore it’s recommended to avoid glass fluid bottles when transporting via fixed-wing aircraft.11 Orthopedic injuries treated with pneumatic splints or casts must also be addressed prior to flight. As air expands, pneumatic splints could become extremely tight causing neurovascular compromise, therefore it’s best to avoid these devices during flight.20
Any patients that have a cast in place will require that the cast be bi-valved prior to flight to prevent potential development of compartment syndrome.7
Basic human functions, such as excretion of bodily fluids (e.g., urination, defecation, salivation, etc.), continues to occur in flight and should be considered prior to flight so that appropriate equipment can be made available.
Some examples of equipment for addressing these functions include personal protective equipment, suction devices, diapers/briefs, sanitary wipes and changes of clothing.
The air medical transport of patients requires intense planning and care with regards to medical issues, yet the non-medical aspects of travel must not be forgotten. Some non-medical considerations include having the appropriate travel documentation/identification for patient, family and crew.
This includes passports and any visas needed for international travel. Specific to international travel, crew members should be sure to have appropriate foreign currency, international electronic charges or adapters, cellular telephone, and access to a map.
When going through customs and border protection screening with a patient, be sure to plan for potential delays. This includes allotting additional time and being prepared to provide any medical care or medication to the patient should there be an extensive delay.
Patients that require invasive hemodynamic support may require placement of an intra-aortic balloon pump (IABP). Some indications for this device include cardiogenic shock, failure to wean from cardiopulmonary bypass, and high-risk percutaneous coronary intervention.25
The IABP is a pneumatic device that’s driven by a computerized console. It’s most commonly placed in a femoral artery, although other large arteries are sometimes used.25
The counterpulsation created by this device leads to balloon inflation during the diastolic phase of the cardiac cycle and balloon deflation during systole. Flight crews that transport patients with an IABP must be familiar with all aspects of the device, as well as how to troubleshoot patient complications and device/console complications.
Prior to transporting a patient with an IABP, preflight checks must be performed. This includes ensuring device compliance with FAA requirements, as the console is considered cargo.25
Also, crews must check helium pressure, battery voltage and electrical load requirements. In addition to the power requirements for the IABP console, there may be additional power needs for ventilators, IV pumps, etc., and careful attention should be paid as to not overload the aircraft’s system.
A fully charged IABP console typically has a battery life of 2–2.5 hours. A test of the equipment should also be performed to evaluate for any interference of communication or navigation equipment.
Once in flight, crew members should focus on close monitoring of the patient’s clinical status, need for medication titration, appropriate functioning of the IABP console and any complications that arise. Patients should have a urinary catheter to allow for close monitoring of urine output. If the intra-aortic balloon migrates to a position that occludes the renal arteries, patients may experience a decrease in urine output.25
Positional changes that occur with flight can impact hemodynamics requiring close monitoring and potential intervention by the flight team. When the patient is positioned with the head of the bed closest to the pilot (i.e., patient facing rear), acceleration forces during takeoff and ascent cause a decrease in preload and a decrease in arterial pressure, which may require fluid resuscitation and/or vasopressor therapy.25
The opposite is true during the deceleration/descent phase. Patients experience increased preload resulting in fluid overload, for which crew members should decrease fluid infusions and have diuretic medication readily available as needed.25
As discussed earlier, altitude changes impact gas expansion, and as the IABP is a pneumatic device, this must be taken into consideration. As altitude increases, volume in the balloon will increase, and as altitude decreases, volume will decrease. The IABP console is capable of monitoring the expansion and contraction of the balloon and will automatically make adjustments as necessary.25
If the console malfunctions, a 60 mL syringe can be used to manually inflate or deflate the balloon. Another potential complication is migration of the balloon. To minimize this risk, the amount of times the patient is moved should be minimized and extreme care should be taken to avoid misplacement of tubes and devices. Also, if the device is placed in the femoral artery, a new immobilizer or splint can be applied.25
The flight crew can assess for balloon migration by monitoring the distal pulses and urine output, and assessing peripheral circulation. Should the balloon migrate during flight, it shouldn’t be removed or adjusted, but instead, the flight crew should promptly notify the receiving facility of the suspected complication to allow for immediate removal or repositioning of the device upon arrival.25
Acute limb ischemia is of real concern when using an IABP and is the most common vascular complication.25
In addition to monitoring peripheral perfusion, the amount of vasopressors should be limited to the minimal amount necessary. In the event of cardiac arrest during flight, ACLS treatment should be immediately initiated, and the pump should be placed in arterial pressure trigger mode. If defibrillation is indicated, it can be performed without disconnecting the IABP.
In patients with advanced cardiac disease that has resulted in severe ventricular dysfunction, implantation of a ventricular assist device (VAD) may be used as a temporizing measure while awaiting cardiac transplant.
These devices may assist the left ventricle (LVAD), right ventricle (RVAD) or both (BiVAD). When these patients require transport via fixed-wing aircraft, a strong understanding of the devices, having appropriate personnel, and familiarity of the crew with aviation medicine is imperative.
Preparation for transport requires having the appropriate equipment, testing of the equipment, having adequate back-up resources, and stabilization of the patient.
Not only should the equipment be considered, but the type of aircraft used is a major factor. Aircraft configuration and range must be able to accommodate the transport. The width and height of the cabin door, cabin size and seating/equipment layout must be conducive to safe patient care.26
maneuvering the patient into and out of the aircraft has been reported as one of the most difficult portions of the transport due to high potential of damaging any extracorporeal pumps.27
In addition to having the appropriate equipment and aircraft, the patient should be placed on the transport pump prior to leaving the transferring facility to ensure that all equipment is functioning properly, and that the patient’s stability remains intact.26
Appropriate equipment for transport includes back-up battery sources, driver consoles, drivers and surge protectors.26
In addition to having the appropriate equipment, adequate medications, blood products and an emergency thoracotomy kit should be available for the duration of the flight.27
Once the flight is ready to commence, the previously discussed physiologic and environmental changes become relevant. Patient positioning impacts hemodynamics as mentioned previously. During acceleration and ascent, gravitational forces cause a decrease in preload thereby leading to a decreased flow rate of the VAD.26
To mitigate this hemodynamic complication, in addition to ensuring pre-transport euvolemia (i.e., fluid volume), awake patients should be asked to contract the gastrocnemius muscles, while sedated patients should have sequential compression stockings applied or have their legs raised.26
As altitude increases, the VAD flow can become potentially decreased, therefore volume replacement and vasopressor therapy are indicated to improve flow rates.27
Also at altitude, humidity is significantly decreased and volume replacement must be performed to ensure proper pump function.27
Patients with severe, refractory circulatory and/or respiratory failure may require extracorporeal membrane oxygen (ECMO) as a potential lifesaving procedure. As ECMO requires intense, complex management, not all medical centers are capable of caring for these patients, therefore patients may require transport in order to receive this treatment option. Transport teams should be experienced in prehospital and transport medicine, intensive care and all aspects of ECMO care.28
As with all patient transports, preparation for flight should include optimal stabilization of the patient and having adequate and functioning equipment, as well as backup equipment, in particular a spare ECMO circuit.29
Additional equipment that’s not commonly included on patient transports but should be available for ECMO transports includes devices such as blood gas analyzers and devices capable of measuring levels of anticoagulation (e.g., activated clotting time machine).29
Specific to preparation of ECMO patients, a dedicated ECMO physician should evaluate the patient at bedside to determine appropriateness of transport and to perform or inspect the cannulation needed for ECMO.29
Due to large oxygen requirements of ECMO patients, it’s imperative that adequate amounts of oxygen are available for the duration of the flight as well as any unexpected delays.29 All equipment must be approved for flight.
Patients transported on ECMO require a team for transport. There are no specific requirements of who should compose the team, however, the Extracorporeal Life Support Organization (ELSO) recommends that a team consist of an ECMO physician, ECMO specialist and transport nurse/respiratory therapist.
The same physiologic and aerospace medicine principles discussed earlier remain relevant to ECMO patients. Some potential complications of transporting ECMO patients, in addition to the potential complications mentioned earlier that are applicable to all patients, include circuit depriming, oxygenator/circuit clotting, inadequate circuit flow and incorrect cannula sizes.29,30
To improve the likelihood of a successful ECMO transport, specialized ECMO teams from high-volume ECMO centers should be involved with the patient transport.29
Obstetric patients that require higher levels of care not available at their primary point of care may require air medical transport to a tertiary facility. It’s cautioned that a fundamental issue in obstetric transports is whether or not the benefits outweigh the risks.31
However, there’s sufficient literature to suggest that transferring obstetric patients to a perinatal center before delivery is associated with improved fetal and maternal outcomes and increase fetal survivability.31,32
The most feared potential in-flight complication by flight crews is delivery, however this is an uncommon occurrance.32,33
Some common reasons for transport include preterm labor (most common), preterm premature rupture of membranes, preeclampsia, eclampsia, vaginal bleeding, pelvic trauma, and multiple gestations.32–34
Most complications experienced in transporting obstetric patients were minor and included nausea, increased contractions, blood pressure changes and decreased maternal respiratory drive, all of which could typically be managed in-flight without need for diversion.32
Increased contractions are a frequent in-flight complication. Therefore, crew members must be adequately trained to treat this condition. Some potential contraindications to transport include untreated incompetent cervix, labor that cannot be stopped with tocolytics, uterine bleeding and severe preeclampsia.34
Prior to transporting an obstetric patient, they should be screened for appropriateness of transfer, potential for development of complications and overall safety. It’s recommended to involve an obstetrician in dispatch for such transfers.33
An important feature of preflight clearance should include fetal positioning to ensure that the fetus is in the vertex (i.e., head down) position, as a breech delivery in-flight can lead to significant neonatal morbidity and mortality.34
Aircraft configuration again is important to ensure enough space for crew to access the pelvis in the unlikely event of an in-flight delivery. Once the patient has been deemed appropriate for transport, medication and equipment checks must be conducted. Specific to obstetric patients, equipment should include emergency delivery kits with instruments to support emergency vaginal delivery, instruments for delivery of neonate (e.g., clamps, suction bulbs, towels, blankets, etc.), and sufficient amounts of gauze and padding.34
In addition to having the correct equipment, specific obstetric medications should be added to the standard transport medications carried by the crew. Typical medications carried by obstetric transport teams include magnesium, terbutaline, oxytocin, steroids and calcium.33,34
As the flight portion of transport commences, the physiologic changes of flight need to be considered. More gravid patients can have compression of the inferior vena cava by the uterus and therefore should be placed in a left lateral decubitus position when possible.
The risk of deep vein thrombosis in pregnancy is increased compared to the general population for multiple reasons, such as hormone and decreased venous return/venous stasis due to gravid uterus.26,34
To mitigate this risk, patients should be allowed to ambulate in the aircraft cabin—when able to do so safely.34
Another aerospace physiologic consideration in obstetric patients is that supplemental oxygen should be used anytime there’s concern that the fetus may be suffering from decreased oxygenation.34
The care of neonates must be performed by healthcare professionals experienced in neonatal resuscitation. Some of the most fragile neonates, and those most challenging to care for during fixed-wing transport, are the patients born at extreme prematurity (less than 28 weeks) and those with extremely low birth weight (less than 1,000 grams).35
Transport personnel must have an understanding of physiologic changes and potential issues that can occur at birth. Some of these changes and issues include fragile skin, increased mobilization of glucose and fatty acids to meet metabolic demands once the maternal supplementation is severed, relative surfactant deficiency, lack of adequate fat cells for insulation, presence of congenital heart disease and maintenance of a patent ductus arteriosus.35
Prior to patient transport, medical optimization should be performed, and discussion should be had with the transferring physician prior to departure from the hospital.
IV access should be established and be in working order. For patients with known or suspected infections, antibiotics and/or antivirals should be continued at the regularly scheduled intervals.
For neonates with respiratory distress syndrome, supplemental surfactant therapy should be initiated prior to transport and invasive airway management with intubation should be performed. Also, for neonates that are ventilator dependent, especially those that will be using a ventilator at home, we recommend that the patients be transitioned to the transport/home ventilator and be stabilized on the ventilator for at least 24 hours prior to the planned transport.
We recognize that 24 hours of stabilization on the transport/home ventilator is not always possible, but every attempt must be made to ensure that the patient is tolerating ventilator settings well prior to exposing them to the unique physiologic challenges experienced at high altitudes. Anemia is another factor that should be addressed prior to flight with a goal of maintaining the hematocrit above 35%.35
In a specific subset of critically ill neonates, those with congenital heart disease, intensive pre-transport resuscitation and stabilization must be achieved. This typically includes airway management and maintenance of a patent ductus arteriosus with the use of prostaglandin E1.
For these patients, transport personnel must be aware of potential side effects of therapy and be capable of managing these effects. In addition to the medical aspects of neonatal transport, the devices (e.g., car seats, incubator, etc.) used throughout flight must be acquired and tested.
For those patients being transported in a car seat, the correct size, harnesses and securing devices are compatible with the plane’s configuration. For these situations, we recommend that a car seat challenge be performed within 12 hours prior to flight.
Close monitoring of patients throughout flight is extremely important. Fluid management, temperature control and prevention/treatment of hypoglycemia are vital to safe transport of the neonate.35
Fluid replacement for infants weighing less than 1,000 grams is typically performed using D5W. One feature unique to neonates is that metabolic acidosis can be quite common. To correct mild acidosis, normal saline boluses are often used, but crews should have sodium bicarbonate available to treat severe acidosis.35
To monitor the adequacy of fluid replacement, monitoring of the heart rate, blood pressure, and urine output can be performed. Another key feature in the stability of neonates is maintaining normoglycemia.
Once a neonate is separated from maternal blood supply and nutrient supplementation, their significant metabolic demands lead to mobilization of glucose from glycogen and triglyceride stores. However, some extremely premature neonates are unable to mount an appropriate response to the increase metabolic demand, thereby depleting glucose stores and being unable to access enough stored glucose-producing products.
This requires the transport team to frequently monitor blood glucose levels and monitor the patient closely for signs of hypoglycemia. Treatment should be initiated to maintain a blood glucose level greater than 45 mg/dL.35
In addition to fluid management and normoglycemia, neonates are extremely susceptible to temperature changes and care must be taken to maintain normothermia.35,36
Occasionally a sea-level cabin is needed to transport patients, but this isn’t the norm. However, in neonates with severe respiratory pathology prior to transport and for patients with congenital heart disease, aircraft cabins should be maintained with a cabin altitude of less than 2,000 feet.35
This will help mitigate the hypoxic effects of altitude. Flight crews must also remember that children with congenital heart disease typically maintain an oxygen saturation in the 80s.
Fixed-wing air transport poses some unique challenges to patient care, however, taking a holistic approach to the patient transfer and using standardized, systematic methods can improve patient safety and quality of care.
Appropriate planning for transport, ensuring adequate supplies and their functionality, thoroughly assessing the patient, and being prepared to response to any potential in-flight complications can create a positive fixed-wing patient transport experience.
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15. Langford S. (2009.) Preparation of patients for transport: General principles. Retrieved Jan. 23, 2018, from www.flyingdoctor.org.au/assets/magazine/file/Preparation_of_Patients_for_Transport_-_Extract_2009.pdf.
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20. Joshi MC, Sharma RM. Aero-medical considerations in casualty air evacuation (CASAEVAC). Med J Armed Forces India. 2010;66(1):63–65.
21. Parode N. (May 17, 2017.) Air travel with portable oxygen concentrators. TripSavvy. Retrieved Feb. 23, 2018, from www.tripsavvy.com/air-travel-with-portable-oxygen-concentrators-2972594.
22. Humphreys S, Deyermond R, Bali I, et al. The effect of high altitude commercial air travel on oxygen concentration. Anaesthesia. 2005;60(5):458–460.
23. Kumar DR, Hanlin E, Glurich I, et al. Virchow’s contribution to the understanding of thrombosis and cellular biology. Clin Med Res. 2010;8(3–4):168–172.
24. Schreijer AJ, Cannegieter SC, Meijers JC, et al. Activation of coagulation system during air travel: A crossover study. Lancet. 2006;367(9513):832–838.
26. McLean N, Copeland R, Casey N, et al. Successful trans-atlantic air ambulance transfer of a patient supported by a bi-ventricular assist device. Aviat Space Environ Med. 2011;82(8):825–828.
27. Potapov EV, Merkle F, Güttel A, et al. Transcontinental transport of a patient with an AvioMed BVS 5000 BVAD. Ann Thorac Surg. 2004;77(4):1428–1430.
28. Broman LM, Holzgraefe B, Palmer K, et al. The Stockholm experience: Interhospital transports on extracorporeal membrane oxygenation. Crit Care Med. 2015;19(278):1–6.
29. Broman LM, Frenckner B. Transportation of critically ill patients on extracorporeal membrane oxygenation. Front Pediatr. 2016;4:63.
30. Bryner B, Cooley E, Copenhaver W, et al. Two decades’ experience with interfacility transport on extracorporeal membrane oxygenation. Ann Thorac Surg. 2014;98(4):1363–1370.
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34. Hurd WW, Rothenberg JM, Rogers RE: Aeromedical evacuation of obstetric and gynecological patients. In W Hurd (Ed.), Aeromedical evacuation: Management of acute and stabilized patients. Springer-Verlag: New York, pp. 287–312, 2003.
35. Wells RJ, Heiman HS, Hurd WW: Pediatric casualties. In W Hurd (Ed.), Aeromedical evacuation: Management of acute and stabilized patients. Springer-Verlag: New York, pp. 329–349, 2003.
37. Brändström H, Sundelin A, Hoseason D, et al. Risk for intracranial pressure increase related to enclosed air in post-craniotomy patients during air ambulance transport: A retrospective cohort study with simulation. Scand J Trauma Resusc Emerg Med. 2017;25(1):50.
· American College of Surgeons Committee on Trauma: Advanced trauma life support (ATLS) student course manual, 9th edition. American College of Surgeons: Chicago, 2012.
· Civil Aerospace Medical Institute, Aeromedical Education Division. (2016.) Introduction to aviation physiology. FAA: Retrieved March 6, 2019, from www.faa.gov/pilots/training/airman_education/media/IntroAviationPhys.pdf.
· Dirnberger D, Fiser R, Harvey C, et al. (May 2015.) Guidelines for ECMO Transport. Extracorporeal Life Support Organization. Retrieved March 6, 2019, from www.elso.org/Portals/0/Files/ELSO%20GUIDELINES%20FOR%20ECMO%20TRANSPORT_May2015.pdf.
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