Aeromedical Evacuation Considerations

Coordinating care between sending and receiving physicians is of paramount importance during patient movement. Neurosurgeons should discuss all patients being transferred to Role 4 with the receiving neurosurgical team to ensure a common understanding of the patient and the risks and benefits of aeromedical evacuation. Casualties with severe TBI should be manifest with altitude restrictions and the cabin pressured to 5000ft. PaO2 and SaO2 should be closely monitored in flight given the risk of barometric changes in PaO2.

INTRACRANIAL PRESSURE

ICP monitoring is recommended during aeromedical evacuation for patients who would meet the requirements stated below in the surgical management section.61

If appropriate neurosurgical capability and bed capacity are available, observation in theater may be warranted for patients with borderline ICP measurements. Stresses of flight including vibration, temperature, noise, movement, light, hypoxia, and altitude have been shown to increase ICP.62,63

Delayed evacuation may improve outcomes in patients with ongoing resuscitation needs and intracranial hemorrhage or decreased GCS. Since most intubated patients require heavy sedation and often paralysis during transport, neurologic exam cannot be followed and a neurologic deterioration may not be detected for many hours. Some patients have suffered herniation during long range evacuation. For example, this has occurred with patients who have significant burns requiring resuscitation who have intracranial hemorrhage or cerebral edema.

Do not remove a functional ICP monitor in the immediate period prior to aeromedical evacuation. This provides information to the Critical Care Air Transport Team (CCATT) team that can direct in flight treatment. Furthermore, it offers a level of safety in terms of stable ICP in patients who may otherwise require sedation or not have a reliable neurological exam.

DRAINS

Do not remove drains in the immediate period prior to aeromedical evacuation due to the risk of bleeding.

PNEUMOCEPHALUS

The effect of increasing altitude on contained air within the body, including the cranium, will potentially result in expansion of pneumocephalus; this is particularly true for those who have not undergone a decompressive craniectomy prior to the flight.

All patients should be transported with head of bed elevation or reverse Trendelenberg at 30-45°. Typically U.S. Air Force doctrine is to load all patient’s feet first into the aircraft.62 In a patient with TBI, the aeromedical transport physician may consider loading headfirst, to maintain head elevation during flight.

DEEP VEIN THROMBOSIS PROPHYLAXIS

All patients should be started on mechanical Deep Vein Thrombosis (DVT) prophylaxis at a minimum using sequential compression devices on uninjured extremities.

All trauma patients who are non-ambulatory require DVT prophylaxis, including brain-injured casualties. Chemical DVT prophylaxis in all moderate to severe head injured patients with normal coagulation profile should be started once there is a documented stable head CT, ideally no later than 24 hours after injury.

Caution in starting DVT prophylaxis and discussion with neurosurgeon is recommended for the following conditions:

- Polytrauma with or at risk for coagulopathy.
- Have intracranial monitor/drain in place.
- Have one or more of the following TBI features that are “high risk” for progression according to the Norwood-Berne criteria:
  - Subdural hematoma (SDH) > 8mm
  - Epidural hemorrhage > 8mm
  - Largest single contusion > 2cm
  - More than one contusion per lobe
  - Diffuse or scattered subarachnoid hemorrhage.
  - Diffuse or scattered intraventricular hemorrhage.

For these patients, chemical prophylaxis may be started 72 hours post-injury or as neurosurgeon recommends (reference) 64,65

Enoxaparin 30mg subcutaneous BID (preferred) or subcutaneous heparin, 5000U TID may be used as chemoprophylaxis.25,66-68