Hypoxic Brain Injury
OVERVIEW
- aka hypoxic encephalopathy; the terms anoxic or ischaemic may also be used
- in adults, typically occurs after cardiac arrest, trauma or drug overdose
- degree of injury proportional to duration and severity of oxygen deprivation to the brain
- brain is entirely dependent on aerobic metabolism and once cardiac arrest takes place oxygen stores are exhausted within 10 seconds
CLINICAL FEATURES
- period of time without circulation or oxygenation to the brain
- coma
- no or abnormal motor response
- myoclonus
PROGNOSIS
AAN Guidelines 2006 state:
“Pupillary light response, corneal reflexes, motor responses to pain, myoclonus status epilepticus, serum neuron-specific enolase, and somatosensory evoked potential studies can reliably assist in accurately predicting poor outcome in comatose patients after cardiopulmonary resuscitation for cardiac arrest.”
“Prognosis cannot be based on the circumstances of CPR.”
“Burst suppression or generalized epileptiform discharges on EEG predicted poor outcomes but with insufficient prognostic accuracy”
NB. These predictors may be confounded by therapeutic hypothermia
Predictors of poor prognosis
- absent pupillary response at 72 hours
- absent corneal reflex at 72 hours
- no motor response or extension to pain at 72 hours (i.e. worse than flexion)
- myoclonic status epilepticus (MSE)
- bilateral absence of cortical SSEPs (N2O response) within 1 to 3 days
- serum neuron-specific enolase >33 μg/L at days 1 to 3
Less useful:
- no CPR for > 8 minutes
- time to ROSC > 30 minutes
- duration of anoxic coma > 72 hours
- Burst suppression or generalized epileptiform discharges on EEG
Predictors of better prognosis:
- recovery of brainstem reflexes within 48 hours (papillary, corneal, oculocephalic)
- return of purposeful response within 24 hours
- primary pulmonary event leading to hypoxaemia
- hypothermia at time of arrest
- young age
INVESTIGATIONS
- EEG: theta activity, diffuse slowing, burst suppression, alpha coma and absence of N20 SSEP (most severe)
- evoked potentials: visual, brainstem and somatosensory (SSEPs) -> test the integrity of neuroanatomical pathways
- CT head and MRI: diffuse oedema or water shed infarcts, loss of grey-white differentiation
- there are other biomarkers in plasma and CSF that are associated with poor outcome (e.g. serum neuron specific enolase, S100 protein)
MANAGEMENT
Resuscitate
- A – intubation for coma, airway protection and prevention of secondary brain injury
- B – titrated O2 to maintain appropriate oxygenation (some data to propose hyperoxia associated with poor outcome)
- C – MAP > 90 ideally to optimize cerebral perfusion, aim for rate controlled SR, pacing
Acid-base and Electrolytes
- aim for normal metabolic state
- support electrolytes
Specific therapy
- identify cause of hypoxic brain injury and treat
- therapeutic hypothermia
- if seizures develop -> anticonvulsants
- normoglycaemia
- no place for steroids, mannitol, Ca2+ channel blockers, high dose barbiturates or glycerol
Underlying cause
- ischaemia: revascularization
- arrhythmia: antiarrhythmics
- congenital:
- electrolyte replacement
- trauma: ATLS protocol
References and Links
CCC Neurocritical Care Series
Emergencies: Brain Herniation, Eclampsia, Elevated ICP, Status Epilepticus, Status Epilepticus in Paeds
DDx: Acute Non-Traumatic Weakness, Bulbar Dysfunction, Coma, Coma-like Syndromes, Delayed Awakening, Hearing Loss in ICU, ICU acquired Weakness, Post-Op Confusion, Pseudocoma, Pupillary Abnormalities
Neurology: Anti-NMDA Encephalitis, Basilar Artery Occlusion, Central Diabetes Insipidus, Cerebral Oedema, Cerebral Venous Sinus Thrombosis, Cervical (Carotid / Vertebral) Artery Dissections, Delirium, GBS vs CIP, GBS vs MG vs MND, Guillain-Barre Syndrome, Horner’s Syndrome, Hypoxic Brain Injury, Intracerebral Haemorrhage (ICH), Myasthenia Gravis, Non-convulsive Status Epilepticus, Post-Hypoxic Myoclonus, PRES, Stroke Thrombolysis, Transverse Myelitis, Watershed Infarcts, Wernicke’s Encephalopathy
Neurosurgery: Cerebral Salt Wasting, Decompressive Craniectomy, Decompressive Craniectomy for Malignant MCA Syndrome, Intracerebral Haemorrhage (ICH)
— SCI: Anatomy and Syndromes, Acute Traumatic Spinal Cord Injury, C-Spine Assessment, C-Spine Fractures, Spinal Cord Infarction, Syndomes,
— SAH: Acute management, Coiling vs Clipping, Complications, Grading Systems, Literature Summaries, ICU Management, Monitoring, Overview, Prognostication, Vasospasm
— TBI: Assessment, Base of skull fracture, Brain Impact Apnoea, Cerebral Perfusion Pressure (CPP), DI in TBI, Elevated ICP, Limitations of CT, Lund Concept, Management, Moderate Head Injury, Monitoring, Overview, Paediatric TBI, Polyuria incl. CSW, Prognosis, Seizures, Temperature
ID in NeuroCrit. Care: Aseptic Meningitis, Bacterial Meningitis, Botulism, Cryptococcosis, Encephalitis, HSV Encephalitis, Meningococcaemia, Spinal Epidural Abscess
Equipment/Investigations: BIS Monitoring, Codman ICP Monitor, Continuous EEG, CSF Analysis, CT Head, CT Head Interpretation, EEG, Extradural ICP Monitors, External Ventricular Drain (EVD), Evoked Potentials, Jugular Bulb Oxygen Saturation, MRI Head, MRI and the Critically Ill, Train of Four (TOF), Transcranial Doppler
Pharmacology: Desmopressin, Hypertonic Saline, Levetiracetam (Keppra), Mannitol, Midazolam, Sedation in ICU, Thiopentone
MISC: Brainstem Rules of 4, Cognitive Impairment in Critically Ill, Eye Movements in Coma, Examination of the Unconscious Patient, Glasgow Coma Scale (GCS), Hiccoughs, Myopathy vs Neuropathy, Neurology Literature Summaries, NSx Literature Summaries, Occulocephalic and occulovestibular reflexes, Prognosis after Cardiac Arrest, SIADH vs Cerebral Salt Wasting, Sleep in ICU
Journal articles
- Wijdicks EF, Hijdra A, Young GB, Bassetti CL, Wiebe S; Quality Standards Subcommittee of the American Academy of Neurology. Practice parameter: prediction of outcome in comatose survivors after cardiopulmonary resuscitation (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2006 Jul 25;67(2):203-10. PMID: 16864809.
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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