Neuro – ICP

Master answer

Intro

ICP: hydrostatic pressure within the cranial vault

• Normal value is 5-15 mmHg
  • focal ischaemia when ICP > 20 mmHg
  • global ischaemia when ICP > 50mmHg

Munro-Kellie

• The rigid and closed cranial vault forms a fixed brain volume containing
  • Brain parenchyma (80%, 1400 g)
  • CSF (10%; 75 mL)
  • Cerebral blood and vessels (10%; 75 mL)
• Δ’s in volume of any components → Δ’s in others

Drugs Control:

Volume of Brain Parenchyma

• Osmotic Agents
  • Mannitol (Response Augmented by concurrent use of Loop Diuretics
  • Hypertonic Saline

Changes in Cerebral Blood Flow (CBF)

• ↑ CBF from ↑
  • CO (thus HR and SV)
    • Inotropes
  • SVR
    • Vasopressors
• ↓ CBF from ↑
  • radius (thus peripheral metab (esp adenosine), incr CO2, decreased O2, vagal stimulation)
    • Induction agents (thiopental) → ↓ CMRO2 → ↓ CO2 production → ↓ CBF → ↓ Volume
    • Other ↓CMRO2 agents
      • Anticonvulsants (phenytoin, levitiractam) → ↓CMRO2 and ↓ Temperature
      • Analgesic (opiods etc)
      • Sedatives (benzodiazepine)
      • Antipyretics should be instituted to reduce fever which will increase metabolic demands
  • viscosity
    • ↑ Free water excretion (frusemide + mannitol)

Volume of CSF

• Acetazolamide (Carbonic Anhydrase Inhibitor): ↓ CSF production

Gladwin 2016

Answer by Gladwin