BRAIN INJURY

1
BRAIN INJURY

• TYPES OF INJURY TO BRAIN TISSUE
• - ischemia
• - excitatory amino acids
• - cerebral edema and ? ICP
• ALTERED CONSCIOUSNESS
• BRAIN DEATH

2
HYPOXIA AND ISCHEMIA

• Brain uses 20 of body O2 consumption
• Hypoxia ? ? brain function, anaerobic
• 
  metabolism
• Severe hypoxia ? cardiac arrest ? global
• 
  ischemia
• Ischemia inadequate blood flow for brain
  metabolic needs
• (global - cardiac arrest, shock focal - stroke)

3
ISCHEMIA

• Glucose and ATP depleted in 4-5 mins
• ? Na/K pump ? ?Nai ? cell edema
• ? Ca2i ?release of enzymes? cell death
• Some changes are reversible if blood flow returns
  rapidly enough
• Deficits which result depend on duration of
  ischemia, sensitivity of brain regions, temp.

4
EXCITATORY AMINO ACID INJURY

• Excitatory a.a. glutamate is involved in many
  brain functions (memory, movement)
• Prolonged ischemia ? ? glutamate reuptake ? ?
  receptor stimulation
  ? ? Ca2 entry ? cell death
• Cerebral cortex and hippocampus are particularly
  vulnerable
• Research into glutamate antagonists, or Ca2
  channel blockers may ? excitotoxic damage

5
? ICP

• Cranium is rigid, fixed volume
• Many types of brain injury ? ? ICP
• Cranial contents brain 80
• blood 10
• CSF 10
• ? ICP ? compression, obstructed blood flow, brain
  tissue displacement herniation
• Normal variations in ICP with respiration,
  straining, coughing

6
? ICP

• Abnormal causes
• ?Tissue tumour, edema, bleeding in tissue
• ?Blood vasodilation (due to hypoxia or ?pCO2),
  ? venous outflow
• ?CSF ? formation,? absoption, ?circulation
• Reciprocal compensation normally occurs between
  the 3 compartments to maintain normal ICP
• ?ICP treatment - monitor,burr hole, diuretic

7
EFFECTS OF ? ICP

• If ICP ? CPP, inadequate perfusion ? hypoxia
  ?confusion ?lose consciousness
• Severely ? ICP with ischemic compression of the
  brainstem ? CNS ischemic response
• (intense vasoconstr., ?BP, wide pulse pr.)
• Downward displacement of brain may ? herniation
  of medulla into foramen magnum ? death

8
? ICP AND BRAIN HERNIATION

• Cranial cavity surrounded and divided by dura
  (falx cerebri, tentorium cerebelli)
• Tentorial notch is the opening for midbrain
• Cerebral arteries and oculomotor nerve (Cranial
  III) pass through, below tentorium
• Brain herniation is displacement of tissue under
  or through membrane spaces
• Compression of oculomotor nerve by down-ward
  herniation ? ipsilateral pupil dilation

9
HYDROCEPHALUS

• ? CSF is usually due to blocked flow or ?
  reabsorption into arachnoid villi
• During development in utero, skull able to
  expand, signs of ?ICP are absent
• In adults, acute or chronic, use shunt or clear
  arachnoid villi

10
ALTERED CONSCIOUSNESS

• Brain injury manifests as altered sensory motor
  function, level of consciousness
• Consciousness has 2 aspects
• - arousal, wakefulness (intact RAS)
• - cognition, awareness (functioning cortex)
• Levels of consciousness a continuum
• conscious-confusion-delirium-stupor-coma

11
COMA AND BRAIN DEATH

• Coma usually follows rostral ? caudal progression
  with characteristic changes in consciousness,
  pupillary response, muscle tone, respiratory
  control
• Glasgow Coma Scale (0-15)
• Brain death irreversible loss of function,
  including brainstem (confirmatory tests)
• Persistent vegetative state loss of cognition
  retain reflex, vegetative functions