1. Objectives
To understand and know:
• The physiology of CSF production and
understand the sign and symptoms of raised ICP
• The pathophysiology of hydrocephalus and its
treatment
2. Intracranial Pressure
• Intracranial pressure is the pressure inside the skull and
thus in the brain tissue and cerebrospinal fluid.
• Normal ICP varies from 5 to 15 mmHg in the adult at rest.
• ICP varies with venous pressure and is thus affected by
factors such as gravitational drainage an manoeuvres that
raise intrathoracic pressure
• Normal values in small children and infants are lower
than for adults.
3. Raised intracranial pressure
• Results in reduced cerebral perfusion and
brain herniation
• The major causes of raised ICP are
haematomas, tumours and hydrocephalus
4. Pathophysiology Of Raised ICP
The Monroe Ke1Iie Hypothesis: lt is the pressure volume
relationship between ICP, of CSF, brain tissue and
Cerebral Perfusion Pressure.
• The hypothesis states that cranium is incompressible and
the volume inside the cranium is fixed.
• The additiOn of a new mass lesion can initially be
compensated for by the egress of CSF and venous blood
from the skull. During this compensation phase, there is
only a small increase in ICP.
• When compensation is maximal, there is then a rapid rise
in ICP. This increased pressure causes compression and
herniation of the brain
5. Raised ICP and CerebrovascularPhysiology
• The brain does not store much energy and is
unable to utilise anaerobic metabolism.
• Cerebral Perfusion Pressure=MAP —ICP
• In normal circumstances, cerebral blood flow is
maintained at a constant rate despite fluctuations
in mean arterial pressure (MAP) of between 50 and
150 mmHg via mechanisms termed cerebral
autoregulation.
• In the injured brain, cerebral autoregulation may
be impaired either locally or globally.
