Increased intracranial pressure
Also known as: intracranial hypertension, elevated ICP
Increased intracranial pressure is a rise in pressure inside the skull above the normal range of roughly 5–15 mmHg, caused by brain swelling, bleeding, tumors, or excess cerebrospinal fluid. It compresses brain tissue and reduces cerebral blood flow.
Increased intracranial pressure (ICP) is an abnormal rise in the pressure within the skull. The Monro-Kellie doctrine explains why it is dangerous: the rigid skull holds a fixed volume of brain tissue, blood, and cerebrospinal fluid (CSF), so an increase in any component — cerebral edema, hemorrhage, tumor, or CSF accumulation (hydrocephalus) — must displace the others or raise pressure.
Rising ICP threatens the brain in two ways. First, it reduces perfusion: cerebral perfusion pressure equals mean arterial pressure minus ICP, so as ICP climbs, blood flow to brain tissue falls. Second, pressure gradients can physically shift brain structures, causing herniation syndromes that compress the brainstem.
Classic findings include headache that is worse in the morning or when lying flat, nausea and vomiting, papilledema on fundoscopic exam, and declining level of consciousness. Cushing's triad — hypertension with widened pulse pressure, bradycardia, and irregular respirations — is a late, ominous sign of brainstem compression. Recognized management principles include elevating the head of the bed, osmotic therapy such as mannitol or hypertonic saline, CSF drainage, and controlled ventilation.
USMLE Step 1 tests the Monro-Kellie doctrine, causes, and herniation syndromes; the NCLEX emphasizes recognizing early neurological changes and Cushing's triad in vital signs; and the CCMA covers increased ICP among traumatic neurological injuries and the medical assistant's role in neurologic examination.
Key takeaways
- Normal ICP is roughly 5–15 mmHg; increases follow the Monro-Kellie doctrine's fixed-volume logic.
- Cerebral perfusion pressure = mean arterial pressure − ICP, so rising ICP starves the brain of blood flow.
- Common causes include cerebral edema, hemorrhage, tumors, and hydrocephalus.
- Cushing's triad — widened pulse pressure hypertension, bradycardia, irregular respirations — is a late sign of brainstem compression.
- USMLE Step 1, the NCLEX, and the CCMA all test increased ICP, from mechanism to bedside recognition.