Intracranial pressure

Intracranial pressure (ICP) is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid (CSF). 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 (intra-abdominal pressure), valsalva maneuver, and communication with the vasculature (venous and arterial systems). Intracranial pressure (ICP) is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid (CSF). 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 (intra-abdominal pressure), valsalva maneuver, and communication with the vasculature (venous and arterial systems). Intracranial hypertension, commonly abbreviated IH, IICP or raised ICP, 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. One of the most damaging aspects of brain trauma and other conditions, directly correlated with poor outcome, is an elevated intracranial pressure. ICP is very likely to cause severe harm if it rises too high. Very high intracranial pressures are usually fatal if prolonged, but children can tolerate higher pressures for longer periods. An increase in pressure, most commonly due to head injury leading to intracranial hematoma or cerebral edema, can crush brain tissue, shift brain structures, contribute to hydrocephalus, cause brain herniation, and restrict blood supply to the brain. It is a cause of reflex bradycardia. Spontaneous intracranial hypotension may occur as a result of an occult leak of CSF into another body cavity. More commonly, decreased ICP is the result of lumbar puncture or other medical procedures involving the brain or spinal cord. Various medical imaging technologies exist to assist in identifying the cause of decreased ICP. Often, the syndrome is self-limiting, especially if it is the result of a medical procedure. If persistent intracranial hypotension is the result of a lumbar puncture, a 'blood patch' may be applied to seal the site of CSF leakage. Various medical treatments have been proposed; only the intravenous administration of caffeine and theophylline has shown to be particularly useful. 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 which may wake them from sleep. The brain is relatively poorly supplied by oxygen as a result of mild hypoventilation during the sleeping hours and also 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 the Cushing's triad. Cushing's triad involves an increased systolic blood pressure, a widened pulse pressure, bradycardia, and an abnormal respiratory pattern. In children, a low heart rate is especially suggestive of high ICP. Irregular respirations occur when injury to parts of the brain interfere with the respiratory drive. Biot's respiration, in which breathing is rapid for a period and then absent for a period, occurs because of injury to the cerebral hemispheres or diencephalon. Hyperventilation can occur when the brain stem or tegmentum is damaged.