CC | PRIMER Acute Brain Injury

Core Intracranial Dynamics (The 20%)

• Volume Distribution: The enclosed skull holds 78% brain tissue, 12% blood, and 10% CSF[1][2].
• Monro-Kellie Doctrine: Intracranial volume is constant; an increase in any component requires compensatory displacement of others to maintain constant volume within the skull[2].
• Key Clinical Target Values: Normal ICP is 5–15 mm Hg (sustained >20 mm Hg is abnormal)[2]. Normal CPP is 60–100 mm Hg (CPP = MAP − ICP)[3]. A CPP <50 mm Hg causes cerebral ischemia, while <30 mm Hg is incompatible with life[3]. Cerebral autoregulation maintains constant blood flow between a MAP of 70–150 mm Hg[2].
• PaCO2 Impact: Elevated PaCO2 causes potent cerebral vasodilation, increasing blood volume and ICP[4].

2. Essential Recognition & Red Flags

• LOC: Change in level of consciousness is the most sensitive and reliable indicator of neurological decline[5].
• Cushing's Triad: Systolic hypertension with widening pulse pressure, bradycardia, and irregular respirations signify brainstem compression and impending herniation[5].
• Pupils & Motor Response: A fixed, unilateral dilated pupil indicates ipsilateral CN III compression[6]. Decerebrate posturing (extensor) reflects midbrain/brainstem damage and is more severe than decorticate (flexor) posturing[6].
• Compliance Loss: A ventriculostomy waveform where P2 is higher than P1 indicates compromised compliance[7][8].

3. High-Yield Condition Comparisons

• Epidural Hematoma (EDH): Arterial tear (middle meningeal artery) causing rapid compression; presents with unconsciousness → lucid interval → rapid decline[9]. Requires emergency surgical evacuation[9].
• Subdural Hematoma (SDH): Venous tear (bridging veins) progressing slower; chronic forms are common in older adults due to brain atrophy[9][10].
• Basilar Skull Fracture: Marked by Battle's sign, raccoon eyes, and CSF otorrhea/rhinorrhea (verified via halo sign or positive glucose)[11][12].
• Bacterial Meningitis: Presents with fever, severe headache, and nuchal rigidity[13]. Diagnostic LP reveals decreased CSF glucose, elevated protein, and high neutrophils[13][14].

4. Priority Clinical Actions

• Airway & Position: Secure airway (GCS ≤8 requires intubation)[15]. Maintain HOB elevated 30 degrees with head midline to optimize venous drainage and CPP[16]. Avoid extreme neck or hip flexion[16].
• Medical Interventions: Administer Mannitol or Hypertonic Saline to draw edema from tissue into circulation[17]. Give prompt IV antibiotics right after cultures for meningitis[14].
• Critical Contraindications: Lumbar puncture is contraindicated with elevated ICP due to herniation risk[18]. Avoid NG tubes and nasotracheal suctioning in basilar fractures/CSF leaks[15][19]. Enforce respiratory isolation for meningococcal meningitis[20].