Intracranial pressure (ICP)

• Normal ICP: <10-15 mmHg, varies w/ age, position, straining, & coughing

ICP & intracranial volume

• Brain parenchyma: 1400 ml (80% total, 10% solid, 70% tissue water)
• CBV: 150 ml (10% total)
• CSF: 150 ml (10% total) (tot. ~1700 ml)

Monro-Kellie doctrine

• ↑ in vol. of one intracranial compartment → ↑ ICP unless offset by ↓ vol. in another compartment
• Brain parenchyma predominantly incompressible fluid, CBV & CSF key in buffering additional intracranial volume by ↑ venous outflow/↓ CBF, displacing/↓ intracranial CSF
• Infants have extra volume compensation w/ open fontanelle
• Pathologic processes can easily ↑ ICP by exceeding compensatory capacity due to small size of CBV & CSF compartments

Pressure-Volume curve

• Additional intracranial volume initially accommodated w/ little/no Δ ICP (flat part of curve)
• Once craniospinal buffering capacity exhausted (decompensation point), small ↑ in intracranial vol. → substantial ↑ ICP

Davson equation

ICP = If * Rout - PSS

• resistance to cerebrospinal fluid outflow (Rout)
• formation of cerebrospinal fluid (If)
• sagittal sinus pressure (PSS)