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Some practitioners prefer it for lumbar puncture in obese patients, where lying on their side would cause a scoliosis and unreliable anatomical landmarks. However, opening pressures are notoriously unreliable when measured in the seated position. Therefore, patients will ideally lie on their side if practitioners need to measure opening 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 and at rest, is normally 7–15 mmHg for a supine adult. This equals to 9–20 cmH 2 O, which is a common scale used in lumbar punctures. [1]
Lumbar puncture is performed to measure the opening pressure, as well as to obtain cerebrospinal fluid (CSF) to exclude alternative diagnoses. If the opening pressure is increased, CSF may be removed for transient relief (see below). [8] The CSF is examined for abnormal cells, infections, antibody levels, the glucose level, and protein levels.
Patients with CSF leaks have been noted to have very low or even negative opening pressures during lumbar puncture. However, patients with confirmed CSF leaks may also demonstrate completely normal opening pressures. In 18–46% of cases, the CSF pressure is measured within the normal range.
Given normal anatomy, the intracranial pressure will be reflected as a rapidly rising pressure measured from the lumbar needle, within 10–12 seconds. If there is a stenosis in the spine, there will be a damped, delayed response in the lumbar pressure, thus a positive Queckenstedt's maneuver.
For example, if a person’s actual blood pressure is 134, and blood pressure is measured on a dangling arm, the reading could end up over 140, which is considered to be stage 2 hypertension.
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Under normal conditions, regular movements such as leaning forward, normal heartbeat and breathing can cause changes to the ICP. Intracranial monitoring accounts for this by averaging measurements over 30 minutes in non-comatose patients. Readings between 7-15mmHg are considered normal in an adult, 3-7mmHg in children, and 1.4-6mmHg in infants. [4]