From the Guidelines
The normal opening pressure for a lumbar puncture (LP) is between 10-20 cmH2O (or 100-200 mmH2O) when measured with the patient in the lateral recumbent position. This pressure represents the hydrostatic pressure of the cerebrospinal fluid (CSF) within the subarachnoid space. Values above 25 cmH2O are generally considered elevated and may indicate conditions such as idiopathic intracranial hypertension, meningitis, subarachnoid hemorrhage, or mass lesions. Conversely, pressures below 6 cmH2O may suggest CSF leakage or volume depletion. When performing an LP, it's essential to have the patient properly positioned with knees drawn to chest and neck flexed to optimize the intervertebral spaces, and to ensure the patient is relaxed as anxiety and pain can transiently elevate the pressure reading. The pressure should be measured before any CSF is withdrawn to obtain an accurate baseline value. The manometer should be held vertically and the measurement taken once the fluid column stabilizes 1.
Some studies suggest that the normal opening pressure may be slightly higher in certain populations, such as children, with a normal range of up to 280 mm of cerebrospinal fluid in children (or >250 mm cerebrospinal fluid if the child is not sedated and not obese) 1. However, these values are not universally accepted, and the generally accepted range of 10-20 cmH2O (or 100-200 mmH2O) is still widely used as a reference point.
It's also important to note that the measurement of opening pressure should be done in a standardized manner, with the patient in the lateral decubitus position, as recommended by recent guidelines 1. This ensures that the pressure reading is accurate and reliable, allowing for proper diagnosis and management of conditions affecting intracranial pressure.
In clinical practice, it's crucial to consider the patient's individual characteristics, medical history, and presenting symptoms when interpreting the opening pressure measurement. A thorough evaluation, including neuroimaging and laboratory tests, may be necessary to determine the underlying cause of elevated or decreased intracranial pressure.
Key points to consider when measuring opening pressure include:
- Patient position: lateral recumbent position
- Measurement technique: manometer held vertically, measurement taken once the fluid column stabilizes
- Normal range: 10-20 cmH2O (or 100-200 mmH2O)
- Elevated pressure: values above 25 cmH2O may indicate conditions such as idiopathic intracranial hypertension, meningitis, subarachnoid hemorrhage, or mass lesions
- Decreased pressure: values below 6 cmH2O may suggest CSF leakage or volume depletion.
From the Research
Normal Opening Pressure for Lumbar Puncture
The normal opening pressure for a lumbar puncture (LP) can vary based on several factors including body position, age, and body mass index (BMI).
- A study published in the Journal of neuro-ophthalmology 2 suggests that the normal range of intracranial pressure (ICP) measured by LP in adults is between 6 to 25 cmH2O, with a population mean of about 18 cmH2O.
- Another study published in Cerebrospinal fluid research 3 measured cerebrospinal fluid (CSF) opening pressure in the lumbar subarachnoid space and found mean pressures of 178.54 mmH2O for the flexed position and 160.52 mmH2O for the relaxed position.
- A more recent study published in The American journal of emergency medicine 4 defined elevated intracranial pressure (ICP) as a CSF opening pressure greater than 25 cmH2O.
- A population-based study published in Frontiers in neurology 5 found that the mean opening pressure was 155.4 mmH2O, with a 95% reference interval of 82-242 mmH2O, and that increasing age was associated with lower opening pressure, while increasing BMI was associated with higher opening pressure.
- A study published in Journal of clinical neuroscience 6 found that elevated lumbar puncture opening pressure (ELPOP) was associated with higher BMI and younger age in patients with aseptic meningitis, with a mean opening pressure of 31.7 cmH2O in the ELPOP group.
Factors Influencing Opening Pressure
Several factors can influence the opening pressure measured during a lumbar puncture, including:
- Body position: The study published in Cerebrospinal fluid research 3 found that the flexed position resulted in higher mean pressures than the relaxed position.
- Age: The study published in Frontiers in neurology 5 found that increasing age was associated with lower opening pressure.
- Body mass index (BMI): The studies published in Frontiers in neurology 5 and Journal of clinical neuroscience 6 found that increasing BMI was associated with higher opening pressure.
- Obstructive sleep apnea (OSA): The study published in Frontiers in neurology 5 found that OSA was more common in participants with higher opening pressures.