Postanoxic Coma - Anoxia

Diagnosis

Indications for Testing

  • Helps aid in predicting outcome in coma >48 hours after anoxic event without evident metabolic or structural etiology

Laboratory Testing

  • Recent reports suggest combining somatosensory evoked potentials (SSEP) with specific serum neurobiochemical markers
    • Neuron specific enolase (NSE)
      • Poor outcome prediction highly likely when N20 SSEP is absent and NSE >33µg/L at 72 hours post-event
    • S-100B protein
      • Levels indicating poor outcome not concretely established
      • Level normals are highly variable in children
      • Not specific for brain injury – increased serum concentrations are found in patients with melanoma, liver and renal injury, inflammation, and infection

Clinical Background

Acquired brain injury (ABI) is caused by a variety of insults, including trauma, stroke, tumor, infection, and hypoxia. A portion of ABI patients suffer from postanoxic coma.

Epidemiology

  • Prevalence
    • ~20% of patients receiving mechanical ventilation
    • 80% of survivors of cardiac arrest are comatose following resuscitation

Pathophysiology

  • Brain oxygen depleted within 20 seconds
  • Central nervous system (CNS) neurons have sufficient glucose stores to support 5 minutes of brain activity
  • Prolonged resuscitation or anoxia does not provide adequate circulation to the brain
  • Brain becomes ischemic, producing cytoxic cascade that activates brain-damaging processes
    • Further damage may ensue and result in neuronal death
    • These processes may result in permanent brain damage
  • S-100B involved in signal transduction and found in glial cells
    • Released into peripheral circulation after neural injury
    • Considered surrogate marker of CNS injury

Clinical Presentation

  • Patient remains unconscious and minimally responsive or unresponsive to stimulation
  • Absent brain stem reflexes – pupil, cornea, gag/cough responses
  • Absent motor responses
  • Absent vestibular reflexes – oculomotor (doll’s eyes and cold calorics)
  • Seizures

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Neuron Specific Enolase 0098198
Method: Quantitative Enzyme-Linked Immunosorbent Assay

Aid in predicting outcome in postanoxic coma

Absolute values not established

Should be ordered with SSEP and used in conjunction with clinical findings

S-100B Protein, Serum 2001766
Method: Quantitative Enzyme-Linked Immunosorbent Assay
Aid in predicting outcome in postanoxic coma

Absolute values not established due to the short half-life and rapid decrease of serum S-100B; knowledge of the time of injury is important for accurate interpretation and outcome prediction

Not specific for brain injury

Should be ordered with SSEP and used in conjunction with clinical findings

Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Neuron Specific Enolase, CSF 0081226
Method: Quantitative Enzyme-Linked Immunosorbent Assay

Adjunctive test

Normal CSF NSE concentrations do not rule out neuronal disease