Page 102 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

70 PART 1: An Overview of the Approach to and Organization of Critical Care

Mode of Transport: The chosen mode of transport for interhospital atmospheric pressure, partial pressure of oxygen, and relative humidity.
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transfers will depend not only on the distance to be traveled, but also Most commercial fixed wing aircraft have their cabins pressurized to
on the stability and physiology of the patient, urgency of transfer, vehicle 8000 ft above sea level with a total ambient pressure of 565 mm Hg
and staff availability, weather conditions, cost, and time of day. 21,22 (75.3 kPa). At this altitude, the partial pressure of oxygen falls to
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Each mode of transport carries its own advantages and disadvantages 65 mm Hg (8.7 kPa). Oxygen saturations in a normal subject will fall
(Table 11-1). Smaller countries, such as the United Kingdom, predomi- to 93% to 94% at this altitude, placing them on the steep part of the
nantly use a road ambulance system for critical care transfers, with air hemoglobin- oxygen dissociation curve. In the nonintubated patient, this
transport used to transfer patients longer distances from isolated areas reduces the oxygen-carrying capacity of blood and increases oxygen require-
or to specialist centers, 22,23 or for trauma retrieval. Larger countries, such ments. Team members may also feel the effects of reduced oxygen tension
as the United States and Australia, rely more heavily on air transport with increased fatigue, dehydration, and poor concentration.
rather than road ambulances. Both the military and private aeromedical According to Boyle’s law, gases increase in volume as pressure decreases
companies provide long-distance transportation by air, bridging con- (at a fixed temperature). At 8000 ft, gas expands by a factor of 1.35. Gas
tinents if required. 24-28 Regulatory bodies such as the Federal Aviation is normally found in a number of body cavities including the middle
Authority (US), Joint Aviation Authority (Europe), and Civil Aviation ear, sinuses, and bowel. Expansion of such gas can cause discomfort and
Authority (UK) stipulate standards for operation of air ambulances. barotrauma. In the critically ill patient, there may be unwanted gas in
Patient transportation by any mode subjects the patient to physi- the thorax, peritoneal cavity, or skull. Expansion of such gas may have
ological changes. All modes, including simple bed movement during an serious consequences. A nasogastric tube should be inserted and placed
intrahospital transfer, expose the patient to the effects of acceleration on free drainage and any pneumothorax should be treated with a chest
and deceleration, as well as motion sickness, vibration, temperature drain with a one-way valve prior to departure. If air transfer is necessary,
change, noise, and anxiety. Air transport can pose hazards to both the some aircraft can pressurize their cabins to sea level, at the expense of
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patient and the escorting team. Studies evaluating the efficacy of air speed, increased turbulence, and reduced fuel efficiency.
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transport show conflicting results, probably due to geographical factors Whichever vehicle is chosen, it must be appropriately equipped to
and differences between systems. A number of studies have concluded transfer a critically ill patient. The vehicle should allow unobstructed
that while transfer times may be shorter by air, this does not always cor- access to the patient, with seating for staff members within close
relate with improved patient outcome. 31-33 Gunnarsson concluded that proximity. The patient, stretcher, and escorting staff must be provided
there were no more adverse events associated with air transport when with appropriate fixing points, harnesses, or seatbelts. Oxygen and suc-
compared to road transportation of pediatric patients whereas Mann tion should be available as well as a power supply compatible with the
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et al concluded that the removal of a rotary aircraft transfer system for equipment used. Patient and staff comfort should be optimized with
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rural intrahospital transfers had increased mortality associated with adequate heating, air conditioning, and lighting. Once the vehicle is
traumatic injuries. When conducted appropriately, transfers by rotary selected, contact should be made with the relevant control center to
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aircraft have been shown to be as safe as road transfers. While major book the transport according to the timings required.
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adverse events during helicopter transfers are rare, minor physiological
events are more common, especially in those patients requiring ventila- Communication: Poor communication is associated with adverse
tory and inotropic support. Air transport causes changes in ambient events during transportation. The team leader is responsible for
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TABLE 11-1 Comparison of Different Modes of Transport
Mode of Transport Advantages Disadvantages Considerations
Land/road ambulance Inexpensive Limited access to very remote locations May require police escort if a rapid move is
required through urban areas.
Ideal for most short distances Slow over long distances Some areas have dedicated critical care ambu-
Usually readily available Limited space lances, these have been recommended by national
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Familiar to most clinicians Speed limited by traffic speed guidelines
Can offer “door-to-door” transfer Frequent changes in acceleration/deceleration forces
depending on traffic speed
Weather independent
Rotary wing aircraft Can cover short to medium distances quickly Limited space Approved aeromedical equipment must be used
Can access remote locations Vibration Crew and medical staff must be trained in man-
Noise agement of in-flight emergencies/evacuation
Requires helicopter landing site procedures
Weather dependent 38
Limited availability of aircraft
Fixed wing aircraft Can cover large distances rapidly Space may be limited in some aircraft Approved aeromedical equipment must be used
Can be used to transfer more than one patient Vibration Crew and medical staff must be trained in man-
at a time Noise agement of in-flight emergencies/evacuation
procedures
Requires a serviceable landing strip and second land
transfer from strip to hospital may be needed
Limited availability of aircraft
Weather dependent
Increased patient anxiety 39

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