Transport Medicine

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225 Transport Medicine

Critically ill patients occasionally need to be moved within an institution or between hospitals. Transport of critically ill patients is a procedure with risks and benefits. Neither the nature and magnitude of risk and benefits nor the variables that might mitigate risks and maximize benefit (e.g., team training and composition, mode of transport) have been well studied. Referral patterns for many diseases, including critical illness, are evolving around centers of excellence. The structure of transport systems and the body of transport research need to keep pace. In order to realize the benefits of regionalization of critical care services, intensivists must take an active role in designing the transport systems and maintaining quality assurance. (Please note that transport issues important to the management of mass casualties in disasters are addressed in Chapter 226.)

image Risks of Transport

Risks of transport are not precisely known. The progression of underlying disease, inadequacy of care delivered during transport, or the physical stress of transport itself can all lead to clinical deterioration of the patient during transport.

The transport environment, given its limited resources and multiple distractions, is bound to be error prone. In a population-based retrospective cohort study of nearly 20,000 air-medical transports, significant adverse events (defined as death, need for major resuscitative measures, hemodynamic deterioration, inadvertent extubation, or respiratory arrest) occurred in 1 in 20 transports. Baseline hemodynamic instability and assisted ventilation before transport and duration of transport were independent predictors of adverse events.1 A retrospective review of voluntarily reported adverse events, which is likely to underestimate the true incidence, reported 11.3 adverse events occurred per 1000 flights.2 The error rate of 1.13% seems low relative to the 2.9% to 16.6% reported incidence of adverse events per hospitalization, but given that the duration of transport is measured in hours, not days, the incidence of adverse events per unit time is quite high.3

The most frequent cause of transport-related adverse events with potential for patient harm is inadequate communication.2 Communication errors are widely recognized to be a major preventable cause of morbidity and mortality in medicine in general. Because interfacility transport involves handoffs between at least three care teams, special care must be taken to ensure that critical details are transmitted. Complete documentation of all patient care records must be sent from the referring facility. Referring physicians should directly communicate the following to both the transport team and the accepting physician: (1) patient identification and medical history, (2) interventions performed during initial stabilization and the patient’s response, (3) pertinent physical examination findings, (4) ongoing therapy, and (5) complications that might occur during transport. The transport team must relay this information to the accepting physician, nurse (RN) and respiratory therapist (RT) in addition to information about the patient’s physiology and interventions performed while en route.

The incidence of adverse events in children is somewhat higher, ranging from 1.5% to 2.8% in transports with a specialized pediatric team to 20% to 61% in high-risk patients transported by nonspecialized teams. Adverse events in pediatric transport tend to be more serious. Airway-related events (loss of endotracheal tube, multiple intubation attempts, malposition of endotracheal tube) are by far the most common adverse event in pediatric transport, followed by loss of critical intravenous (IV) access, sustained hypotension, and cardiac arrest.46

image Rapid Transfer, Goal-Directed Therapy, and the Golden Hour

Emergency medical services (EMS) and regional flight teams tend to work under the assumption that the time between the moment of injury and arrival at a center capable of delivering definitive care is among the most important determinants of survival. This notion has been taught for 3 decades but is based on little or no evidence and has recently been scrutinized. Time from scene departure to arrival at the hospital was not associated with survival in out-of-hospital cardiac arrest, and transport time including scene time was not associated with survival in trauma.7,8 At the time the “golden hour” was conceived, prehospital care consisted of providing supplemental oxygen, a fast-moving vehicle, and minimal resuscitation. Under these circumstances, a worse outcome could be expected as prehospital time increased.

Belief in the golden hour may lead to risky behavior. High speeds occasionally result in crashes with injury to EMS providers as well as patients, and EMS have an occupational risk of death similar to that of policemen or firefighters.

There are certainly disease processes—aneurysms requiring neurosurgical intervention, thrombotic events requiring directed thrombolysis, complete transposition of the great arteries requiring urgent atrial septostomy, for example—in which rapid transport to a center that can provide definitive care is the most pressing issue. These are rare in children and, although reasons for interfacility transport of adult patients have not been studied, are likely to represent a small fraction of all critical care adult transports.

In pediatric patients, respiratory failure and shock are the most common reasons for transport. A recent study identified shock in 37% of children transferred to tertiary centers, regardless of reason for referral.9 In adults and children, protocolized, aggressive, early therapy of septic shock has proven vastly more effective than any pharmacologic intervention at improving mortality.1012

Pediatric protocols recommend aggressive fluid resuscitation, initiation of inotropes, and administration of antibiotics within the first hour after presentation.13 The recommended treatments are simple interventions that can be initiated in community emergency departments (EDs) and continued and refined in transport, provided the treating physician and transferring team appreciate the urgent need and are sensitive to the subtle signs of shock in children. Han et al. reported that when community physicians aggressively resuscitated and successfully reversed shock before a transport team arrived, patients had a ninefold increase in their odds of survival.11 These studies defy the popular notion that out-of-hospital stabilization wastes time and delays definitive therapy that should be rendered at the receiving facility.

Although adult guidelines are more relaxed, there are no data to suggest that it is safe to delay goal-directed therapy for transport. In fact, in adults with septic shock, a delay in antibiotic therapy is associated with worse survival, with mortality increasing by 7% for every 30 minutes that passes without delivery of appropriate antibiotic therapy. The golden hour in transport is the time from presentation to initiation of appropriate treatment, treatments that should be initiated at the referring facility and continued and refined by the transport team.14

image Regionalization of Critical Care

Significant advances in therapeutic and diagnostic interventions for critically ill patients have occurred, but often at great cost and limited availability, prompting the need for transport of these patients to tertiary care centers. A recent consensus conference on prioritizing the organization and management of intensive care services in the United States (PrOMIS) suggested that intensive care would be optimally delivered in a tiered regionalized system.15 Ideally, regionalization would reduce practice variation, improve adherence to best practices, and reduce costs by realizing economies of scale. Regionalization would necessarily result in an increased number of transfers of critically ill patients from lower-volume to higher-volume centers, so the PrOMIS conference proposed that regionalization must be coupled with a regionalized emergency transportation system.

Emergent interfacility transport should occur after initial stabilization and determination by the referring facility that the patient’s needs for care are beyond the scope of local capabilities. In trauma, neonatal intensive care, and pediatric intensive care, the accepting physician serves as an expert who can guide pretransfer stabilization and ensure the safety of transport. Over time, local or low-volume hospitals will have less and less experience with critically ill patients. The transport system may be a useful avenue for education of referring physicians. Receiving centers should have communication centers that facilitate transfers, outreach teams to provide referring facilities with continuing education, and education programs about regional resources and trauma systems.

image Out-of-Hospital Transport

Prehospital Transport

EMS are focused on rapid assessment, stabilization, and transport from the scene to the nearest ED or trauma center that can render appropriate care. Patient management is usually limited to supporting the airway, breathing, and circulation. The transport team should also be able to perform a needle thoracostomy if indicated, control active bleeding, and establish venous access. Other procedures should be kept to a minimum.

Out-of-hospital tracheal intubation by paramedics has recently come under fire. Despite the fact that tracheal intubation is the standard of airway management in the hospital and that tracheal intubation has been practiced by paramedics for 25 years, few studies support a survival benefit of tracheal intubation over bag-valve mask ventilation in the prehospital setting. Tracheal intubation is a complex skill rarely performed by paramedics. Failure rates are high, and multiple attempts are common; both of these may be accompanied by hypoxemia and other physiologic deterioration.16 When intubation is successful, tracheal tube dislodgement during transport by EMS is common; tracheal tube misplacement or dislodgement rate at the time of arrival to ED varies from 5.8% to 12% for adults to 25% for pediatrics.1618 Finally, uncontrolled hyperventilation during manual ventilation by the EMS crew may be deleterious in head-injured patients and during cardiopulmonary resuscitation (CPR).

Appropriate utilization of resources (air versus ground units) for the prehospital transport of injured patients has been a subject of study and debate since the inception of air medical transport. In general, air medical transport is associated with both shorter transport intervals and a greater medical capability of the transporting team. The decision to use air transport in the prehospital setting should be supported by on-line medical control or preapproved protocols based on the factors of time, distance, geography, patient stability, and local resources. The National Association of Emergency Medical Service Physicians (NAEMSP) and the American College of Emergency Physicians (ACEP) have each recommended triage guidelines for on-scene helicopter transport.19 Retrospective studies have shown improved outcomes in patients transported by air, particularly major trauma patients and patients with severe traumatic brain injury.2024 Defining the types of specific injuries or medical conditions that benefit from air medical transport has been difficult. As specialized cardiac and stroke centers have developed, air transport has begun to be utilized for rapid transport of these patients directly from the scene.

Interfacility Transport

Most interfacility transfers do not involve critically ill patients and can be accomplished safely a local EMS under predefined protocols or with specific instructions from a command physician. In rural areas, use of local EMS for interfacility transfer risks depleting a large geographic area of valuable medical resources such as ambulances, emergency medical technicians, and paramedics. The referring physician, who has little control over the en route phase of the transport, assumes a significant legal risk. Because of the variable backgrounds of EMS staff, the transferring personnel may not be equipped or trained to provide the necessary care in every situation. In particular, most EMS providers have little experience with critical care beyond the immediate resuscitative measures commonly performed in the prehospital setting, and they may not be trained in the use of certain hospital equipment (e.g., drug infusion pumps.)

In some situations, referring hospital staff may accompany a local ambulance service. The legal risk is reduced because the referring physician maintains tighter control over the patient’s treatment during the transfer. Disadvantages of this option include loss of personnel from the referring hospital and lack of appropriate portable monitoring equipment.

Patients may also be transferred by a regional retrieval system, most of which are centered around air medical transport. Because air medical transport systems are used to transfer sicker patients and are held to a higher standard, the medical teams on these flights offer significantly greater medical capability compared with ground ambulance EMS.

In many instances, regional retrieval teams can also provide ground transport using personnel whose training and experience are held to the higher standard of air medical transport. Air medical transport team members are usually specially trained to deal with out-of-hospital emergencies and are acclimated to the stress of working in a moving environment. The team routinely carries equipment to manage deterioration during transfer and has battery-powered portable monitoring devices designed for use in moving environments. A command physician who is usually based at the institution from which the team originates provides recommendations for management until the team arrives.

Specialty teams provide an even higher level of expertise in the care of selected patients, the largest group being pediatric and neonatal critical care teams. Transport teams with specific expertise in left-ventricular assist devices or extracorporeal membrane oxygenation also exist. In many areas, however, specialty teams are unavailable. Because these teams tend to be based at tertiary care centers, time between decision to transfer and team arrival at the bedside may be longer than for local EMS or a regional air medical team. Specialty teams often perform additional stabilization maneuvers before leaving the referring facility. This practice has been criticized as prolonging bedside time and thus overall transport time interval. In reality, the time to definitive care may be shortened in many critically ill patients transferred by specialty teams. With these teams, the intensive care unit (ICU) is brought to the patient.

In most areas at the time of this writing, regional critical care teams are synonymous with air medical transport teams. However, the U.S. military has developed critical care transport teams with significantly greater capabilities that may serve as a model for critical care specialty civilian teams. In the mid 1990s, the U.S. Air Force began to develop what has come to be called the critical care aeromedical transport team (CCATT.) The team consists of a nurse, respiratory therapist, and physician, all with experience in critical care as well as specific training pertinent to functioning in the transport environment. The teams carry resources to create a mobile ICU, including ventilators, mobile ultrasound equipment, and point-of-care laboratory testing. They go far beyond resuscitation and are able to recognize and manage multiple organ failures. The composition of these teams and details on the equipment and pharmacology they carry are described in an excellent article by Grissom and Farmer.25 In the military, these resource-intensive teams are routinely used to manage up to three critically ill patients in a single transport. Although this model cannot be precisely duplicated in the civilian world, the experience of these teams must be considered when transport systems are designed to support regionalization of critical care.

Issues Specific to Air Medical Transport

Most air medical transport today is done with twin-engine helicopters specially configured for medical missions. The practical transport range for helicopter transfers is generally 150 miles from the craft’s base of operations. For longer-distance transports or in poor weather conditions, fixed-wing aircraft are used by many air medical services. Some flight programs are able use rotorcraft in instrument-flight-rules missions, allowing transport of patients in weather conditions that would otherwise preclude helicopter transport. This method requires filing of a flight plan, which may introduce delay.

The helicopter environment is noisy, so auscultation of blood pressure and breath sounds in flight is difficult if not impossible.26 To monitor patients in flight, transport teams must rely on methods that do not depend on audible sounds: noninvasive blood pressure monitoring, capnometry, and pulse oximetry, to name a few.

Rotorcraft produce significant vibrations, making simple procedures difficult. Most therapeutic interventions such as tracheal intubation, chest decompression, IV access, and control of bleeding must be done before liftoff. The threshold for intubation in pediatric patients undergoing helicopter transport should be slightly lower than in those undergoing ground transport. Intravenous analgesia, sedation, neuromuscular blockade, vasoactive drugs, and blood products can be given in flight. These interventions must be performed under strict on-line medical direction or preapproved protocols.

Barometric pressure changes associated with increasing cabin altitude lower alveolar oxygen tension, increase the volume of any entrapped gas (e.g., in the bowel, sinuses, pneumothorax, endotracheal tube cuffs), and may affect IV infusion rates.

Rotorcraft rarely fly at altitudes more than 2000 feet above ground level. At these altitudes, pressure changes have only a minor impact on the volume of air-filled spaces. The relatively small volume of air in the tracheal tube cuff may be subject to clinically significant pressure changes at that altitude. A recent prospective study found that 98% of patients had tracheal tube cuff pressures above 30 mm Hg, and 72% had intracuff pressures above 50 mm Hg during helicopter transport at a mean of 2260 feet.27 Tracheal tube cuff pressures should be measured and adjusted during flight.

Ventilators are calibrated for performance at sea level. Most flights maintain a cabin pressure equivalent to 6000 to 8000 feet. In the United States, Federal Aviation Administration regulations mandate cabin altitude less than 8000 feet. Ventilators that recognize and compensate for changes in barometric pressure exist (Uni-Vent Eagle Model 754 [Impact Instrumentation Inc., West Caldwell, New Jersey]) but are not in common use outside the military. Tidal volumes delivered by the LTV 1000 (Pulmonetic Systems Inc., Minneapolis, Minnesota), a commonly used transport ventilator, may vary from 5% to 12% at a simulated altitude of 4000 and 8000 in volume control mode. At 15,000 feet, LTV-delivered tidal volumes may be 30% to 37% greater than set tidal volumes.28 Similar findings have been reported with the Drager Oxylog ventilators (Dragger, Telford, Pennsylvania). Ventilators that use pneumatic circuits for respiratory rate control may deliver lower rates and increased tidal volumes at high altitude.29

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