Raised intracranial pressure (ICP)
Concise, exam‑focused summary of pathophysiology, clinical recognition and initial emergency management of raised intracranial pressure in head injury and other acute neurological presentations. Key UK sources: NICE NG232 (Head injury: assessment and early management), RCEM guidance on NG232, Resuscitation Council UK guidance on ventilation/hyperventilation, and NICE materials on subarachnoid haemorrhage and lumbar puncture safety.
Physiologic basics
- ICP is the pressure inside the rigid craniospinal compartment that contains brain tissue, blood and CSF. Normal supine adult ICP ≈ 5-15 mmHg.
- Monro‑Kellie principle: intracranial volume is fixed; an increase in one component (brain, blood, CSF) must be offset by reduction in another (CSF/venous outflow) until compensatory reserve is exhausted, after which small volume increases cause large ICP rises.
- Cerebral perfusion pressure (CPP) = MAP - ICP.
- Rising ICP reduces CPP unless MAP is supported; reduced CPP causes cerebral hypoperfusion and secondary brain injury.
Common causes
- Focal mass lesions: extradural haematoma, subdural haematoma, intracerebral haematoma, contusion.
- Diffuse brain swelling/oedema: traumatic, hypoxic/ischaemic, encephalitis.
- Tumour or abscess.
- CSF flow obstruction: communicating or obstructive hydrocephalus.
- Venous outflow obstruction: cerebral venous sinus thrombosis or external compression.
- Systemic contributors: severe hypertension, hypercapnia, raised intrathoracic pressure.