ICP monitoring provides continuous measurement of pressure within the cranial vault, enabling early detection of dangerous elevations and guiding therapy. Normal ICP is 5-15 mmHg; sustained pressures above 20 mmHg require intervention. The external ventricular drain (EVD/ventriculostomy) is the gold standard — it measures ICP AND allows therapeutic CSF drainage. A catheter is placed into the lateral ventricle (usually right, non-dominant hemisphere) and connected to a fluid-coupled transducer and drainage system. The intraparenchymal monitor (e.g., Codman or Camino) is a fiber-optic or strain-gauge sensor placed directly into brain tissue — it cannot drain CSF but has lower infection risk and does not require releveling. ICP waveforms provide critical information about intracranial compliance: P1 (percussion wave) originates from arterial pulsation transmitted through choroid plexus; P2 (tidal wave) reflects brain tissue compliance; P3 (dicrotic wave) follows the dicrotic notch. In normal compliance, P1 > P2 > P3 (descending staircase). When P2 exceeds P1 (ascending morphology), intracranial compliance is DECREASED — the brain cannot accommodate further volume increases and herniation risk is elevated. Lundberg A waves (plateau waves: sustained ICP elevations to 50-100...