Episode Details

Intracranial Regulation & Monro-Kellie Doctrine The skull contains brain tissue (78%), blood (12%), and CSF (10%). Under Monro-Kellie, because this volume is constant, an increase in any one component must be offset by displacing another; otherwise, intracranial pressure (ICP) rises. Compensations include displacing CSF, collapsing cerebral veins, and compressing tissue. Decompensation causes ischemia. Normal ICP is 5 to 15 mm Hg; sustained pressure >20 mm Hg is abnormal.

Cerebral Perfusion Pressure (CPP) & Blood Flow CBF requires constant O2 and glucose. Autoregulation maintains constant CBF when MAP is between 70 and 150 mm Hg. CPP = MAP - ICP. Normal CPP is 60 to 100 mm Hg; <50 mm Hg causes ischemia and neuron death, while <30 mm Hg is incompatible with life. Hypercapnia (high PaCO2) and acidosis dilate cerebral vessels, increasing CBF and ICP.

Pathophysiology of Worsening ICP Insult triggers edema, compressing ventricles and vessels. This decreases CBF, causing hypoxia and brain cell death. The resulting acidosis and hypercapnia trigger vasodilation, raising blood volume and worsening ICP in a lethal feedback loop. Unrelieved pressure causes brainstem compression and downward herniation through the foramen magnum, causing respiratory arrest and death.

Assessment & Clinical Findings

• LOC: The most sensitive indicator of neurologic status.
• Cushing’s Triad: Systolic hypertension with widening pulse pressure, bradycardia, and irregular respirations—an emergency indicating impending herniation.
• Ocular: Compression of CN III causes an ipsilateral fixed, dilated pupil, indicating herniation.
• Motor: Rising ICP leads to decorticate flexion (cortical interruption) or decerebrate extension (midbrain/brainstem damage; arms stiff, hyperpronated).
• CSF Leak: Rhinorrhea/otorrhea from basilar fractures poses a high meningitis risk. Confirm CSF via glucose testing or the halo sign (yellow ring around blood) on gauze.

Interventions & Management

1. Airway first: Intubate if GCS ≤ 8. Limit suction to <10s and 2 passes, pre-oxygenating with 100% O2.
2. Positioning: Elevate HOB to 30 degrees midline to promote venous drainage, avoiding extreme hip/neck flexion.
3. Osmotherapy: Give IV Mannitol (25%) or Hypertonic Saline to shift fluid from cells into vessels. Monitor sodium and osmolality.
4. Diagnostics: Head CT is the gold standard. Lumbar puncture is contraindicated due to herniation risk.
5. Ventriculostomy: Gold standard for monitoring ICP. Level the transducer with the tragus of the ear. If P2 wave is higher than P1, compliance is compromised.