Intracranial pressure

Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 mmHg for a supine adult. The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF. Changes in ICP are attributed to volume changes in one or more of the constituents contained in the cranium. CSF pressure has been shown to be influenced by abrupt changes in intrathoracic pressure during coughing (which is induced by contraction of the diaphragm and abdominal wall muscles, the latter of which also increases intra-abdominal pressure), the valsalva maneuver, and communication with the vasculature (venous and arterial systems). Intracranial hypertension (IH), also called increased ICP (IICP) or raised intracranial pressure (RICP), is elevation of the pressure in the cranium. ICP is normally 7–15 mm Hg; at 20–25 mm Hg, the upper limit of normal, treatment to reduce ICP may be needed. In general, symptoms and signs that suggest a rise in ICP include headache, vomiting without nausea, ocular palsies, altered level of consciousness, back pain, and papilledema. If papilledema is protracted, it may lead to visual disturbances, optic atrophy, and eventually blindness. The headache is classically a morning headache that may wake the person up. The brain is relatively poorly supplied by oxygen as a result of mild hypoventilation during the sleeping hours leading to hypercapnia and vasodilation. Cerebral edema may worsen during the night due to the lying position. The headache is worse on coughing, sneezing, or bending and progressively worsens over time. There may also be personality or behavioral changes. In addition to the above, if mass effect is present with resulting displacement of brain tissue, additional signs may include pupillary dilatation, abducens palsies, and Cushing's triad.