Introduction

Helicopter-based emergency medical services (HEMS) evolved from rudimentary transportation-only services to advanced, critical-care capable units offering some of the most advanced prehospital care. HEMS offers many benefits, including expeditiously accessing rural or remote locations, providing multiple advanced crew configurations, and intervening when ground-based units are unavailable. However, HEMS utilization must be weighed against the disadvantages of rotor-wing flight, including the inherent risk of crashes that result in subsequent injuries or deaths to crew members or patients. Other considerations for HEMS use include changes in physiology associated with flight, cost, and limited resource expenditure. Given the risks and benefits of HEMS, certain guidelines should be considered to determine the need for HEMS response. Establishing the indications and contraindications for HEMS can greatly reduce the stress of requesting providers during stressful patient encounters. As always, guidelines should be used with clinical judgment case-by-case basis.[1][2][3][4]

Issues of Concern

Many organizations, including the American College of Emergency Physicians (ACEP), the National Association of EMS Physicians (NAEMSP), and the Air Medical Physician Association (AMPA), have recommendations for appropriate utilization of HEMS. When considering HEMS activation, evaluation of the following items, as outlined by the NAEMSP, can help determine appropriate HEMS activation:

• From a clinical standpoint, does the patient require minimal transport time outside the hospital or critical care setting?
• Are there time-critical evaluations or treatments for the patient that are required but unavailable at the referring facility?
• Are ground units able to access the patient for timely transport?
• Are the predicted and current weather conditions along the expected path and nearby areas amenable to rotor-wing flight?
• Do the patient and all accompanying equipment fall within the size and weight limitations of the aircraft?
• Are helipads, airports, or improved landing zones available near the referring and receiving hospitals?
• Can ground-based personnel provide the patient's care requirements, or does the patient require a higher level of care only available in an HEMS unit?
• Can local ground transport services adequately provide a local response if a unit is taken out of service for prolonged transport?
• Is regional ground-based critical care transport a viable alternative to HEMS transportation?

Recommendations for HEMS activation are not intended to replace clinical judgment or to be the sole determinators of which patients should be transported by HEMS units.

Clinical Significance

Several principles should be kept in mind when considering HEMS activation. First and foremost, critical care resources should be provided to patients who require them as rapidly as possible. Patients who are critical or unstable require transport as rapidly as possible and likely require critical intervention during transport. Time to destination for definitive care is a consideration, and delays should be minimized. The most appropriate crew should be used to transport more stable patients using the most suitable mode of transportation. Ground-based critical care may be more appropriate when a patient requires critical care during transport and more rapid transport is not required. Furthermore, stable patients who do not require critical care during transport may be best served by local EMS or noncritical care transport unless doing so would burden the system. Mass casualty or disaster incidents may also necessitate using HEMS to provide extended capabilities, extra personnel, or rapid treatment and transport of critically injured or ill patients.[5][6][7]

Scene Trauma Considerations

Scene responses by HEMS units typically involve trauma patients. In an age of regionalized trauma care, rapid aeromedical transport of trauma patients helps provide earlier definitive care and delivery of treatment to help stabilize critically injured patients. The NAEMSP recommendations for scene response include the following as possible indications for HEMS activation for trauma patients:

General

• Trauma score of less than 12
• Unstable vital signs
• Significant trauma in patients less than 12 years old or older than 55 years old
• Significant trauma in pregnant patients
• Multisystem trauma injuries, including multiple long bone fractures and two or more injured body regions

Mechanism

• Penetrating head, neck, chest, thoracic, abdominal, or pelvic trauma
• Crush injury to the head, chest, or abdomen
• Ejection from a vehicle
• Pedestrian or cyclist struck by a motor vehicle
• Death in the same passenger compartment as the patient
• On-scene EMS personnel concern for the patient’s vehicle compartment
• Fall from a significant height
• Near drowning and drowning injuries

Neurological injuries

• Glasgow coma scale (GCS) less than 10
• Declining mental status
• Obvious skull fracture
• Exam and presentation concerning spinal cord injury 

Thoracic injuries

• Major chest wall injury, including flail chest or open chest wound
• Pneumothorax or hemothorax
• Suspected cardiac injury

Abdominopelvic injuries

• Significant abdominal pain after blunt trauma
• Seatbelt sign or other abdominopelvic contusions
• Obvious rib fracture(s) below the nipple line
• Suspected major pelvis fracture (open pelvis fracture, unstable pelvis fracture, suspected pelvis fracture with hypotension)

Orthopedic and extremity injuries

• Partial or total amputation of a limb, excluding digits
• Finger or thumb amputation when an emergent surgical evaluation is required but not available by rapid ground-based transport
• Fracture or dislocation with vascular injury or compromise
• Extremity ischemia
• Open long bone fractures
• Two or more long bone fractures

 Burns

• Greater than 20% of total body surface area (TBSA) burns
• Burns to the face, head, hands, feet, or genitals
• Inhalation burn or injury
• Electrical or chemical burns
• Burns with associated injuries

Although the above list is extensive, individual system requirements, destination facility resources, availability, and geographic location influence HEMS activation. For example, a motor vehicle crash involving several patients in a large metropolitan area with a trauma center 20 minutes from the scene via ground transport would not typically warrant HEMS activation; however, a mass casualty incident in the same location might necessitate HEMS use. Alternatively, a motor vehicle crash with 2 critical patients in a county served by 2 advanced life support (ALS) units 45 minutes from the hospital would almost certainly be appropriate for HEMS activation. In this case, the patients benefit from rapid transport and critical care capabilities while preventing the depletion of that county’s ALS resources if both units are required for transport.

More recently, Thomas et al attempted to develop an evidence-based guideline for using HEMS for trauma patients. Although a lack of high-quality research confounded their efforts, they proposed guidelines based on the Centers for Disease Control and Prevention (CDC) 2011 Guidelines for the Field Triage of Injured Patients.

Medical and Interfacility Considerations

Regionalization of care is commonplace and likely to continue as hospital systems grow and merge. This allows for the centralization of advanced care and provides previously unavailable specialty care to more patients by transfer agreements and referrals. Timely transport of patients requiring critical interventions can often be accomplished via ground-based units. Still, certain conditions may benefit from rapid aeromedical transport and the capabilities provided by HEMS units. The NAEMSP identified the following conditions and possible indications for HEMS transport of medical and interfacility patients.

Trauma

• Any patient identified in the list above who cannot be managed sufficiently at the referring hospital
• Patients with identified or suspected injuries that are beyond the capabilities of the referring hospital, such as intrathoracic, intraabdominal, or intracranial injuries identified in the primary or secondary survey or adjunct imaging

Cardiac

• Acute coronary syndromes, including ST-segment elevation myocardial infarction (STEMI) require advanced intervention, including cardiac catheterization, intra-aortic balloon pump, or emergent surgery
• Cardiogenic shock requiring advanced intervention
• Cardiac tamponade requiring advanced intervention
• Mechanical cardiac disease, including acute or worsening valvular disease and acute cardiac rupture

Neurological

• Central nervous system hemorrhage (intracranial hemorrhage, epidural hematoma, among others)
• Mass lesion resulting in spinal cord compression
• Ischemic stroke requiring thrombolytic or intra-arterial therapy not available at the referring hospital
• Status epilepticus

Obstetrics

When considering aeromedical transport for obstetric patients, it is extremely important to weigh the risks and benefits of HEMS. Delivery of an infant while in flight in a helicopter is challenging at best and may be impossible due to airframe limitations. Patients at risk of imminent delivery are best served by ground-based critical care units in which delivery of the infant is more manageable. Nevertheless, situations may exist where distance, crew capabilities, or referring hospital limitations may necessitate using HEMS to transport an obstetric patient. Such indications may include:

• Delivery of the infant would require obstetric or neonatal care not available at the referring hospital
• Active premature labor when the estimated gestational age (EGA) is less than 34 weeks or the estimated fetal weight (EFW) is less than 4.4 pounds (2000 grams)
• Eclampsia or severe pre-eclampsia
• Third-trimester hemorrhage
• Hydrops fetalis
• Maternal comorbidities that could result in premature delivery
• Severe predicted fetal disease or illness that cannot be managed at the referring hospital
• Acute maternal abdominal emergencies that require surgery before 34 weeks EGA or EFW less than 4.4 pounds (2000 grams)

Neonatal

Similar to cardiac and trauma care, neonatal care may be highly regionalized. While many neonates do not require rapid transport to a referral center, they still require advanced care in regional centers. In many cases, HEMS can deliver specialized personnel and equipment to a referring hospital, stabilizing a neonate. Following stabilization, transport to the regional neonatal center may be best accomplished via a ground unit, allowing the HEMS unit to return to service. Ground transport times greater than 30 minutes may be an indication for HEMS transport of neonates and should be considered on a case-by-case basis. Neonates with the below conditions may benefit from HEMS activation.

• EGA less than 30 weeks or weight less than 4.4 pounds (2000 grams)
• Significant neonatal complications, including cardiac or respiratory arrest, sepsis, meningitis, hemodynamic instability, temperature instability, or significant metabolic abnormality
• Oxygen supplementation with a fraction of inspired oxygen (FiO₂) greater than 0.6 (60%), positive airway pressure such as CPAP, or mechanical ventilation
• Pneumothorax, interstitial emphysema, or extrapulmonary air leak
• Seizures, congestive heart failure, or disseminated intravascular coagulation
• Surgical emergencies requiring capabilities not available at the referring hospital

Other Medical or Surgical Patients

Patients who require care beyond what is available at a referring facility may be candidates for HEMS transport. These patients can often be cared for by ground-based critical care units. However, some patients are too unstable to remain out of a hospital for the duration of a ground-based transport. In these cases, HEMS transport may be a viable alternative.

• Resolved cardiac or respiratory arrest exceeding the referring facility's capabilities
• Vasopressor requirement
• Mechanical ventilation requirements or advanced mechanical ventilation strategies such as inverse-ratio ventilation
• Potential airway deterioration not yet definitively managed
• Toxicology care requiring a bedside toxicologist or care otherwise not available at the referring facility
• Urgent hyperbaric oxygen requirement
• Urgent dialysis
• Gastrointestinal bleeding requiring blood products or hemodynamic management
• Surgical emergencies requiring specialized care (aortic dissection, ischemic limbs, among others)
• Pediatric patients requiring care exceeding the referring facility's capabilities

Cardiac arrest patients who remain in cardiac arrest are rarely appropriate for HEMS transport and activation. Cardiopulmonary resuscitation (CPR) cannot be safely performed in an aircraft, although mechanical CPR devices may allow safe CPR.

Autolaunch

Autolaunch or auto dispatch is a concept in which a 911 dispatch center activates a HEMS unit automatically upon receipt of a call. Typically, criteria are predetermined locally so that when met, a HEMS unit is placed on standby or dispatched simultaneously with the ground-based EMS crew. Crews on standby typically complete pre-flight preparations and await final activation before lifting off. In certain regions, an autolaunch can reduce the response time to a scene, quickly provide care, and shorten transport times. Data concerning autolaunch impacting patient outcomes is sparse, but some reviews show that it reduces response times and lengths of stay in the hospital. 

Mission Acceptance

Typical HEMS crews consist of a pilot and 2 or 3 medical providers. In an attempt to prevent flight crews from feeling pressured into accepting missions, many HEMS organizations notify flight crews only of destinations so that they may determine if a mission is acceptable from a weather and safety standpoint. Details of the mission beyond destinations are given only when the mission is deemed safe for the crew. HEMS programs may participate in a notification service like www.weatherturndown.com, which allows programs to post declined missions. Declined missions are visible to all users to prevent "helicopter shopping," whereby a referring facility requests HEMS activation from nearby programs when the initial HEMS program declines the mission. Direct dispatch, whereby a local 911 dispatcher calls the HEMS base and directly requests a HEMS unit, potentially bypasses multiple safety layers built into the call triage and dispatch process and should be discouraged. All HEMS programs should have a dispatch center that fields all service requests, allowing missions to be triaged, evaluated for safety by the flight crew, and appropriately tracked.

Conclusion

HEMS activation is a constantly evolving field. Regionalization of specialty resources, access to remote locations, advanced in-flight care, and referring hospital capabilities influence HEMS use. As a critical component of any regional EMS system, HEMS must be appropriately utilized to benefit the greatest number of patients. These guidelines are intended to offer a framework for appropriate HEMS activation and do not serve as a replacement for clinical assessment and decision-making.