Intracranial Pressure

Intracranial pressure

  • Intracranial Pressure
    –    Skull is an enclosed space with three variables
    –    Brain tissue
    –    Blood
    –    Cerebrospinal fluid

–    Mechanisms that control total volume in    cranial vault (chamber) contribute to maintenance of normal ICP.

–    Brain tissue accounts for 80% of total volume, composed of neurons and glial cells plus interstitial and intracellular fluids.
–    Cerebral blood volume accounts for 10% of total cranial volume, affected by cerebral blood flow. Vessel diameter is affected by small changes in carbon dioxide levels, a slight increase causing vasodilation and increased cerebral blood flow.
–    Cerebrospinal fluid is 10% of total cranial volume. Constant volume of only 125-150ml even though production is 500-700ml/day. Produced by choroid plexus in ventricles, reabsorbed via arachnoid villi.
Increase Intracranial Pressure
–    Increase intracranial Pressure or  hypertension is when intracranial pressure exceeds 15 mmHg, with a pressure range of 10-20 mm mercury possibly requiring intervention. Pressures over 30mm mercury warrant (demand) immediate attention.
–    Any increase in volume of one component without decrease of another will result in IICP. (Mass lesions increase brain tissue volume: tumor, abscess, hematoma. Increase in CSF volume if unable to circulate CSF out or be reabsorbed: acute transition hydrocephalus, chronic increase in CSF).

*    Other factors that influence intracranial pressure
–    Arterial pressure
–    Venous pressure
–    Intraabdominal and intrathoracic pressure
–    Posture
–    Temperature
–    Blood gases

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