- Intracranial Pressure
– Skull is an enclosed space with three variables
– Brain tissue
– 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
– Blood gases