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Cerebrospinal fluid (CSF) opening pressure is a measurement of the pressure found inside the spinal canal when a care practitioner initially penetrates it to collect a sample of fluid for analysis. Doctors routinely note the CSF opening pressure because it can provide important information about a patient's health. Tests are not usually performed just to measure pressure; if a patient's pressure is a cause for concern and a doctor recommends monitoring, the patient's skull may be fitted with a device to measure pressure inside the brain case. Variations in CSF opening pressure can be a sign of disease, or of an improperly performed test.
To measure CSF opening pressure, a care provider carefully inserts a needle into the spinal canal in a procedure known as a lumbar puncture or spinal tap. The patient needs to lie in a slightly curled position and hold still during this procedure. An anesthetic makes it more comfortable. Once the needle is in place, the care provider can attach a meter and allow the CSF to flow up into the meter until it levels out. The care provider bases the CSF opening pressure measurement on the amount of fluid collected.
This information is noted in millimeters of water (mmH2O); while the cerebrospinal fluid actually contains a mixture of compounds, not just water, this is the standardized measurement used. In very young children, it may be as low as 10 mmH2O, while obese adults may have pressure as high as 250 mmH2O. The doctor can consider the patient's age and size when comparing the pressure measurement to a chart of normal ranges to determine if the patient's pressure is abnormal.
Patients in shock or coma tend to have a low CSF opening pressure, as do patients who have just fainted and those with low blood pressure. High pressure is typically the result of high pressure inside the skull, which may be caused by injury, improper drainage of CSF, hemorrhage, and other issues. The care provider can also evaluate the sample of CSF collected during the pressure measurement to check for signs of disease like clots of white blood cells that indicate inflammation.
The care provider can note the CSF opening pressure on the patient's chart and may also make a note of the collection technique used during the procedure. This assures that anyone reviewing the chart understands the circumstances of the measurement. If a measurement appears to be off, care providers may consider the fact that an error could have been made during the measurement. In this case, the patient's pressure might not actually be abnormal, or the doctor might need another test to check.