Introduction

An acquired brain injury (ABI) refers to damage sustained by the brain after the time of birth and is therefore not caused by a congenital abnormality. Examples of ABI include the various types of stroke, infections such as meningococcal meningitis and any injury to the brain from physical trauma. This article discusses some of the issues involved in the aeromedical retrieval of this patient group. Secondary / tertiary retrieval missions, during which a patient is transferred from a hospital facility to another healthcare facility, such as a hospital in another country, is the main focus for discussion. Primary retrieval of brain-injured patients is also common, and typically involve helicopter emergency medical services (HEMS); these are referred to at the end of the article.

Acquired brain injury is increasing in frequency and represents a significant burden for healthcare providers, including within the aeromedical transfer and retrieval sector. The latest figures from Headway (the Brain Injury Association charity based in the UK) show that in 2016-17, there were 348,453 admissions to UK hospitals with ABI. That represents 531 admissions per 100,000 population, and a National Health Service (NHS) admission occurring approximately every 90 seconds. Admissions with ABI have increased in the UK by 10 per cent in the last 10 years.1

Sufferers from ABI may be left with devastating and life-changing loss of brain function, including disorders of thinking, feeling, talking and walking. Survivors of ABI, their families and carers often require significant degrees of help and support in the aftermath of injury. When ABI occurs away from home, for example when on holiday or when working overseas, patients and their carers have an even greater level of difficulty and distress. Aeromedical transfer providers have an important role in delivering patients and relatives to the comfort of familiar surroundings and a healthcare system more able to service complex long-term medical and rehabilitation requirements. Crucially, the patient transfer, although in itself is unlikely to improve the outcome for the patient, should not cause further harm. It should certainly be as painless and stress-free as possible during an undoubtedly difficult time.

Primary and secondary brain injury

The clinical pathology of ABI is commonly referred to as ‘primary’ and ‘secondary’ brain injury. Primary brain injury refers to the damage caused to the brain at the time of the event. This would include, for example, direct trauma to the brain resulting from a serious road traffic collision. By definition, the damage caused in primary brain injury has happened before there was an opportunity to perform medical interventions. Little can be done later to mitigate this.

Aeromedical transfer providers should aim to prevent secondary brain injury during patient transportation and continue therapies and management strategies already in place with this aim

Secondary brain injury is that which occurs in the hours, days and weeks after the primary injury has occurred. Examples would include complications from impaired blood flow to healthy areas of the brain due to swelling and raised intracranial pressure. Medical interventions following ABI are generally aimed at preventing or reducing secondary brain injury. Aeromedical transfer providers should aim to prevent secondary brain injury during patient transportation and continue therapies and management strategies already in place with this aim

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Preventing and reducing secondary brain injury

The Brain Trauma Foundation (BTF) Guidelines for management of severe traumatic brain injury (TBI) are now in their fourth edition2. In this patient group, good quality evidence for interventions that improve outcomes with good functional recovery remains lacking. General principles involve managing raised intracranial pressure (the pressure within the cranial vault), targeting cerebral perfusion pressures (the pressure driving blood flow to the brain) and avoiding even short periods of hypoxia and hypotension.

Cerebral perfusion and blood pressure targets

Cerebral perfusion pressure (CPP) can be calculated when the intracranial pressure (measured from a direct indwelling pressure monitor or ‘bolt’) is subtracted from the mean arterial blood pressure. The BTF advocate targeting a CPP of 60-70mmHg following TBI (level IIb evidence). Blood pressure should be targeted as maintaining a systolic blood pressure >100mmHg in patients 50-69 years old and >110mmHg in patients 15-49 or over 70 years old (level III evidence).

Simple measures such as ensuring the tube ties (on intubated patients) are not so tight that they occlude venous drainage, and sitting the patient at 30-45 degrees to aid venous drainage and minimise fluid shifts during take-off and landing are well-known and commonly practised.

Other therapies

Other therapies such as osmotherapy and decompressive craniectomy are used, but evidence of long-term improvement in outcomes remains lacking. Active cooling is no longer advocated and, instead, the maintenance of normothermia and avoidance of hyperthermia are important principles used in many neurosurgical intensive care units. Phenytoin or Keppra (Levetiracetam)3 may be used following brain injury as prophylaxis against seizures; however, post-traumatic seizures have not always been associated with worse outcomes2.

Stroke

In the UK, recent emphasis has been placed on the rapid diagnosis of stroke in the pre-hospital environment and expedited transfer of the patient to a tertiary specialist stroke centre. Ambulance services often use pre-hospital triage tools such as FAST (face-arm-speech-test). Tertiary units are able to provide specialist advanced interventions such as stroke thrombolysis. The London Hyper-Acute Stroke model has improved patient outcome by offering such specialist services whilst saving the NHS money4, 5.

Practicalities of transporting the brain-injured patient

There are times (such as in the acute phase of the illness or immediately following a deterioration in condition) when ABI patients may be less suitable for transfer and the risks of undertaking such a mission may outweigh the benefits. Any transportation of a patient in the early stages following serious injury, either within the confines of a hospital or outside, can be difficult and dangerous for the patient. During an aeromedical transfer, particularly, there are the issues associated with cabin pressure, relative hypoxia and the physical forces placed on the body, particular under heavy acceleration and deceleration during take-off and landing.

Air ambulance or commercial airliner

The decision relating to the platform on which to transfer a patient depends on the complexity and acuity of the injury. This is also sometimes influenced by financial constraints, particularly when the retrieval mission is to be privately funded by individuals, as opposed to through an insurance policy. In these circumstances, if a commercial airliner is to be used, it is generally wiser to wait for relative patient stability, removal of tubes and lines and when the risks of any patient deterioration during flight is felt to be low. In more complex injuries requiring a higher level of care and where the risks of patient deterioration during flight are felt to be higher, it is generally accepted that an air ambulance would be the transfer modality of choice.

Acute phases of illness

In the days immediately following ABI, patients are often unstable. TBI patients may well have other traumatic injuries, which require complex intensive care prior to transfer. Intracranial pressure is often labile and significant fluctuations can occur on minimal patient movement. In these situations, it is often prudent to wait until the clinical picture is more stable and more favourable. However, there may be a perceived need to quickly move such a patient to a higher level of care, from a remote area or location with only basic medical facilities and less able to manage the case. Clearly, a thorough risk assessment needs to be made and individualised to each case, taking these factors and others into account.

a thorough risk assessment needs to be made and individualised to each case, taking these factors and others into account

If intracranial pressure monitoring is still in-situ, in the form of a bolt or an extra-ventricular drain, this may indicate that the patient remains somewhat unstable in terms of their head injury. Caution should be taken when considering transfer of these patients. Intracranial pressure monitors are often removed when a period of stability has been achieved and when the likelihood of further deterioration (such as a re-bleed from an aneurysm) is lower.

Moving patients with intracranial pressure monitors can therefore be more hazardous, both in terms of a labile intra-cranial pressure and in managing the devices themselves in the flight environment. Retrieval providers may wish to wait for removal of these devices and the patient stability that this infers. However, this needs to be balanced against the clinical urgency of the transfer.

Post-neurosurgery

If the patient has required some form of brain surgery, the clinical picture is likely to take some time to stabilise post-operatively. Following some types of surgeries, air may be present within the cranial vault. This in itself rarely causes a problem, but if there is no route of egress for this air, problems can be encountered during transfer. At normal cabin pressures of 5,000-8,000ft, humidified air may expand by up to 30 per cent and this expansion could cause dangerous rises in intracranial pressure. A period of days, or sometimes even weeks, may need to elapse to facilitate safe repatriation. Direct consultation between the aeromedical retrieval team and the treating neurosurgical team is good practice.

Direct consultation between the aeromedical retrieval team and the treating neurosurgical team is good practice

In cases where transfer is needed expeditiously, careful consideration of using a lower cabin altitude throughout the flight needs to be made. Any decision to fly at lower altitudes, and hence at a sea-level cabin pressure, needs to be balanced against the additional time taken for such a transfer, which may also negatively impact the patient.

Agitation and delirium

Following ABI, it is common for patients to experience disorders of cognition. The ‘irritable brain’ may lead to patients becoming agitated, difficult to manage and potentially a danger to themselves and / or the transferring team. Clearly, this is particularly important in the confines of an aeromedical retrieval mission, with the safety of the aircraft, patient and crew at the forefront of considerations.

Agitation and delirium can sometimes settle with the course of time and again it may be prudent to wait if there is potential for resolution of these symptoms. However, should transfer be indicated, effective plans for managing agitation, including controlled and targeted pharmacological sedation, should be agreed during the planning phase.

References

1. Headway. The Brain Injury Association. www.headway.org.uk. Website accessed November 2018

2. Carney N, Totten A, et al. Guidelines for the Management of Severe Traumatic Brain Injury. 4Th Edition. September 2016. Brain Trauma Foundation

3. Chaari A, Mohamed AS. Levetirecetam versus phenytoin for seizure prophylaxis in brain injured patients: a systematic review and meta analysis. In J Clin Pharm. 2017 Oct; 39(5): 998-1003

4. Jauch EC, Saver JL. et al. Guidelines for the Early Management of Patients with Acute Ischemic Stroke. AHA/ASA Guideline. 2013

5. Bouverie J. Major changes in stroke care can save lives. Blog. www.england.nhs.uk 19 July 2017

6. Whitely S. MacCartney I. et al. Guidelines for the transport of the critically ill adult (3rd Edition 2011). Intensive Care Society

7. National Institute for Health and Care Excellence. NG39. Major trauma: initial assessment and management. February 2016