Aeromedical Transport

Aka: Aeromedical Transport, Air Ambulance, Helicopter EMS, Helicopter Ambulance, Rotor Wing Aircraft Medical Transport, Fixed Wing Aircraft Medical Transport

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II. Epidemiology

  1. Incidence of air transport in U.S.: 550,000 per year (2026)

III. Indications

  1. General Indications
    1. Acceleration of time-sensitive interventions (time saved significantly improves outcomes)
    2. Specialized care en-route
  2. Multisystem Trauma (or Trauma with AMPT Score >=2)
    1. Transfer to Level 1-2 Trauma Center
    2. Air Medical Prehospital Triage (AMPT Score) >=2
      1. Consider Helicopter Emergency Medical Services (HEMS) transport (increased survival)
  3. Acute Myocardial Infarction
    1. Emergent revascularization
  4. Severe Burn Injury
    1. Burn Center transport
  5. Acute Heart Failure
    1. Refractory management (Intra-aortic balloon pump, LVAD, ECMO, transplant candidate)
  6. Cerebrovascular Accident
    1. Reperfusion in large vessel Occlusion
  7. Sepsis
    1. Intensive management in refractory cases (ECMO, Proning, advanced goal directed therapy)
  8. High Risk Pregnancy
    1. Transport to maternal fetal medicine (e.g. HELLP Syndrome, surgical interventions)
    2. Neonatal ICU available (e.g. severe prematurity)
  9. Pediatric or Neonatal patient
    1. Severe Illness (e.g. PICU, NICU)
    2. Significant comorbidity (e.g. Congenital Heart Disease)

IV. Contraindications

  1. Logistic factors
    1. Adverse weather conditions (flight grounded)
    2. Resource availability
    3. Distance
      1. Ground EMS within 30 miles may be faster in urban and suburban communities
  2. Patient factors
    1. See specific condition management below

V. Pathophysiology

  1. See High Altitude Related-Conditions
  2. Ambient air pressure (atmospheric pressure) decreases with increasing altitude, allowing for an increase in Gas Volume
    1. Allows trapped air (e.g. Pneumothorax) to expand
    2. A helicopter transport with 5000 foot rise from sea level
      1. Results in a pressure drop (14.7 psi to 12.7 psi)
      2. Results in a Gas Volume increase of 15-20%
        1. Boyles Law states P1*V1=P2*V2
  3. Oxygen Partial Pressure decreases with altitude related drop in total Ambient air pressure (atmospheric pressure)
    1. Oxygen maintains its percentage (21%) of overall gas constituents in atmospheric pressure (78% Nitrogen, 1% Argon)
    2. However, Oxygen Partial Pressure drops in relation to total atmospheric pressure decrease
      1. DRY Sea level Partial Pressure: 160 mmHg (21% of total atmospheric pressure, 760 mmHg)
      2. DRY Partial Pressure at 5000 feet: 132 mmHg (21% of total atmospheric pressure, 630 mmHg)
    3. Partial Pressure is lowered by the humidified, heated air we inspire through our upper airways
      1. Saturated vapor pressure at Body Temperature (98.6 F or 37 C) is 47 mmHg
      2. Alveolar Partial Pressure of oxygen at sea level = 0.21 * (760 - 47 mmHg) = 0.21 * 713 = 150 mmHg
    4. Decreased oxygen Partial Pressure results in fewer oxygen molecules available on inspiration of a given Lung Volume
      1. Hypoxia risk increases

VI. Types

  1. Helicopter Transport (rotor wing aircraft)
    1. Travels 100-150 mph and can transport directly between facilities (assuming helipad availability)
    2. Not pressurized, and typically at <3000 feet elevation (gas expands 15%, unless crossing mountains)
    3. Unable to fly during poor weather conditions or decreased visibility as limited by visual flight rules (VFR)
    4. Mobile Intensive Care Unit level of care (unless air rescue helicopters which are typically BLS or ALS)
    5. Endotracheal Tube cuffs may need adjustment (Foley Catheter and Gastric Tube cuffs may remain unchanged)
    6. Discuss small Pneumothorax pre-flight management (consider Chest Tube before transport)
    7. Safety: 2.5 accidents per 100,000 flight hours in 2016 (non-medical accident rate 30 per 100,000 hours)
    8. Air Ambulance transport costs as of 2019, frequently exceed $50,000, often only partially paid by insurance
      1. Helicopter companies operate on a single digit profit margin
      2. Costs per mile are most expensive, followed by 24 hour readiness staffing and supplies
      3. Helicopter purchase, medical refitting and maintenance are also very expensive
      4. In rural areas, households may subscribe at $50-80/year to cover emergent Ambulance transport
      5. Swadron and Farah in Herbert (2019) EM:Rap 19(9): 1-2
  2. Fixed Wing Aircraft Transport
    1. Travels 250 to 600 miles per hour, and preferred for distances >200 miles
    2. Travel at higher altitude and cabin pressurized to 7000 feet (gas expands 30%)
    3. Less limited by weather than helicopter as fixed wings can travel by instrument flight rules (IFR)
    4. Mobile Intensive Care Unit level of care
    5. As with helicopter, Endotracheal Tube cuffs and small Pneumothorax are pre-transport considerations

VII. Adverse Effects

  1. Trapped gas expansion
    1. Example: Pneumothorax (see pathophysiology above)
    2. Decompress trapped gas before transport (e.g. Chest Tube, Nasogastric Tube)
    3. Consider ground transport in high risk cases (e.g. intraocular bubble)
  2. Hypoxia
    1. Due to lower oxygen Partial Pressure (see pathophysiology above)
    2. Administer Supplemental Oxygen
    3. Consider pre-transport Endotracheal Intubation
  3. Aircraft Noise and Vibration
    1. Limits patient assessment and interventions
    2. Increased patient stress and anxiety
      1. Obtain consent from patient for air travel and discuss what they may experience in flight
      2. Consider Anxiolytics in the peri-flight period
      3. Provide comfort measures (warm blankets, ear protection)
  4. Fluid Shifts during take-off and landing
    1. Tilt of aircraft and patient positioning may result in trendelenburg positioning (or reverse)
    2. May affect cerebral perfusion or venous return
  5. In-flight decompensation
    1. Unstable Patients pre-flight are more likely to decompensate in the air
    2. Increased decompensation risks
      1. Hemodynamically Unstable Patients (MAP <60 mmHg, SBP <80 mmHg, Vasopressors)
      2. Mechanical Ventilation
    3. Prevention
      1. Perform thorough assessment and diagnostics before transport
      2. Resuscitate and stabilize as much as possible before transport
      3. Complete important stabilization procedures before transport (e.g. reliable IV Access, Chest Tube)
      4. Maintain inflight fluid Resuscitation (including dextrose containing solutions for children)
  6. Venous Thromboembolism
    1. Consider VTE Prophylaxis (Anticoagulation and Compression Stockings) in prolonged air travel (hours)
  7. Aircraft Accident
    1. Helicopter EMS: 1.8 fatalities per 100,000 flight hours
  8. Financial Costs, Insurance Coverage and Medicolegal Liability
    1. Helicopter EMS Cost (U.S. 2026): $25,000 to $60,000 (up to $100,000)
    2. Fixed Wing EMS Cost (U.S. 2026): $12,000 to $50,000
    3. Carefully document indications for air transport
    4. Documentation points
      1. Clinical urgency
      2. Failure of Alternatives
      3. Medical contraindications to ground transport (if present)
      4. Nearest appropriate facility

VIII. Management: Specific Conditions Peri-Transport

  1. Pneumothorax
    1. Risk of progression to Tension Pneumothorax
    2. Decompression with Chest Tube prior to air transport is often recommended
  2. Small Bowel Obstruction or recent abdominal surgery
    1. Gas expansion risk (bowel ischemia, wound dehiscence, impaired lung excursion)
    2. Consider nasogastric or orogastric descompression prior to transport
  3. Pneumocephalus (Basilar Skull Fracture, recent neurosurgery)
    1. Intracranial air expansion may risk sudden increase in Intracranial Pressure
  4. Intraocular Bubble (recent Vitrectomy, pneumatic retinopexy)
    1. Intraocular bubble expansion risks Retinal Artery Occlusion and irreversible blindness
    2. Air flight may be contraindicated
      1. Except if cabin pressure can reliably be maintained at sea level (default cabin pressure is 7000 feet)
  5. Acute Mountain Sickness (and High Altitude Cerebral Edema)
    1. Returning to altitude for transport may exacerbate conditions
  6. Decompression Sickness
    1. May be a contraindication to air travel (weigh risks versus benefit in severe Decompression Sickness)
    2. Altitude related pressure changes may be offset with other interventions
      1. Intravenous Fluids
      2. Supplemental Oxygen
      3. Lower altitude transport (or sea level cabin pressurization)
    3. Decompression Sickness may be exacerbated by air travel
      1. Atmospheric Pressure at 5000 feet: 12.2 psi
      2. Atmospheric Pressure at sea level: 14.7 psi (1 ATA or atmosphere absolute)
      3. Total Pressure at Depth 66 feet: 3 ATA (44 psi)
    4. Compressed air contains inert gas (e.g. Nitrogen)
      1. As divers descend to higher water pressures, more nitrogen gas is dissolved in the blood stream (Henry's Law)
      2. As divers ascend to lower pressures, gradual off-gassing of nitrogen is required
    5. Rapid ascent (decompression) does not allow for adequate nitrogen off-gassing
      1. Insoluble nitrogen bubbles instead precipitate, resulting in Decompression Sickness

IX. References

  1. Aydin, Fritz, Duncan and Cohen (2022) Crit Dec Emerg Med 36(10): 23-29
  2. Katzer (2018) Crit Dec Emerg Med 32(6): 3-10
  3. Shen (2026) Crit Dec Emerg Med 40(9): 4-13

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