Brain Impact Apnoea

OVERVIEW

• brain impact apneoa is an under-appreciated cause of morbidity and mortality in traumatic brain injury (TBI)
• hypoxia can markedly worsens outcome in TBI
• aka ‘impact brain apnoea’
• rapid correction (e.g. by bystanders) of brain impact apnoea may facilitate full neurological recovery

PATHOPHYSIOLOGY

The first 10 minutes following TBI has been described as ‘the critical phase’ (it is followed by exponential, plateau and resolution phases) and is thought to involve 2 key components:

• apnoea
• catecholamine surge

Apnoea

• Always occurs with concussive head injury
• greater the energy delivered to the brain, the longer the subsequent apnea and the poorer the respiratory recovery
• In severe forms respiratory recovery does not occur spontaneously, leading to death without resuscitation at the scene
• Prolonged apnoea causes:
  • hypoxia over a period of minutes leading to direct neuronal injury and cell death
  • hypercapnia resulting in cerebral vasodilation and increased cerebral blood volume
  • the end result can be massive, early cerebral oedema resulting in death or poor neurological outcomes
• in addition to centrally driven apnoea, obstructive apnoea resultant from loss of airway patency may also occur

Catecholamine surge

• massive sympathetic discharge occurs resulting in hypertension
• hypertension compounds hypercapnia-induced cerebral vasodilatation resulting in early vasogenic edema, endothelial injury, and blood-brain barrier disruption
• intracranial pressure (ICP) progressively increases depending on the magnitude of the adrenergic surge and hypercapnia
• other vascular beds may develop sustained vasoconstriction, resulting on complications such as  ischemic gastric mucosal ulceration and neurogenic pulmonary oedema
• direct catecholamine tissue injury can occur, such as myocardial necrosis

ASSESSMENT

Clinical features

• history of traumatic brain injury
• apnoeic since time of impact
• respiratory failure may progress to lethal cardiac arrest unless there is appropriate intervention

Imaging

• CT Head (may be normal, underlying severe anatomical injury may or may not be present)

MANAGEMENT

• requires prompt prehospital intervention (e.g. by bystanders, may be facilitated by innovations such as the GoodSam app)
• open airway (with cervical spine protection if appropriate)
• correct hypoxia and hypoventilation
• if cardiac arrest has not supervened some patients will spontaneously rouse or be extubated neurologically intact after further investigation (sometimes with a normal CT head)
• start usual severe TBI management if required (see TBI Management)

References and Links

Journal articles

• Atkinson JL. The neglected prehospital phase of head injury: apnea and catecholamine surge. Mayo Clin Proc. 2000 Jan;75(1):37-47. Review. PubMed PMID: 10630756. [Free Full Text]
• Wilson MH, Hinds J, Grier G, Burns B, Carley S, Davies G. Impact Brain Apnoea–a forgotten cause of cardiovascular collapse in trauma. Resuscitation. 2016. [article]

FOAM and web resources

• St.Emlyn’s — Impact Brain Apnoea with Gareth Davies from London HEMS (2015; podcast)
• Spanos A. Impact brain apnoea: a critical phase of head injury. 2021