From the Guidelines
Normal opening pressure, measured during a lumbar puncture, typically ranges from 10 to 20 cmH2O (or 70-200 mmH2O) in adults when lying in the lateral recumbent position. This pressure represents the cerebrospinal fluid (CSF) pressure in the subarachnoid space, as noted in the study by 1. Values may be slightly higher in obese patients or those who are anxious and tensing their abdominal muscles during the procedure. Children generally have similar normal ranges, though infants may have slightly lower values. Factors that can artificially elevate opening pressure include being in a seated position rather than lateral recumbent, holding breath, straining, or having legs extended rather than flexed during measurement.
The most recent and highest quality study, 1, although focused on a different context, does not provide a conflicting range for normal opening pressure, thus the established range of 10 to 20 cmH2O (or 70-200 mmH2O) remains applicable. Opening pressure is an important diagnostic parameter that helps identify conditions like idiopathic intracranial hypertension (elevated pressure) or CSF leaks (decreased pressure). The measurement should be taken before any CSF is removed to ensure accuracy, with the patient relaxed and breathing normally. It's also worth noting that the definition of elevated intracranial pressure can vary, with some studies like 1 defining it as an opening pressure of 1200 mm H2O or higher in the context of cryptococcal meningitis, but this does not alter the normal range.
Key points to consider:
- Normal opening pressure range: 10 to 20 cmH2O (or 70-200 mmH2O)
- Positioning during measurement: lateral recumbent position
- Factors affecting measurement: obesity, anxiety, breathing, and muscle tension
- Importance of accurate measurement: diagnosis of conditions like idiopathic intracranial hypertension or CSF leaks.
From the Research
Normal Opening Pressure
The normal opening pressure is a topic of discussion in the medical field, with various studies providing insights into its definition and influencing factors.
- The normal range of intracranial pressure (ICP) measured by lumbar puncture (LP) in adults is considered to be 6 to 25 cmH2O (95% confidence intervals), with a population mean of about 18 cmH2O 2.
- However, there is considerable variability, with some normal individuals having pressures of 30 cmH2O or even higher, emphasizing the need to interpret pressure measurements in the clinical context 2.
- A population-based study found that the mean opening pressure was 155.4 mmH2O, with a 95% reference interval of 82-242 mmH2O, and increasing age was associated with lower opening pressure, while increasing body mass index (BMI) was associated with higher opening pressure 3.
Factors Influencing Opening Pressure
Several factors can influence opening pressure, including:
- Age: Increasing age is associated with lower opening pressure 3.
- Body Mass Index (BMI): Increasing BMI is associated with higher opening pressure 3.
- Obstructive Sleep Apnea (OSA): Presence of OSA is associated with higher opening pressure 3.
- Abdominal circumference: Increased abdominal circumference is associated with increased cerebrospinal fluid (CSF) pressure in patients with spontaneous intracranial hypotension (SIH) 4.
- Symptom duration: Longer symptom duration is associated with increased CSF pressure in patients with SIH 4.
Clinical Implications
The variability in opening pressure highlights the importance of considering individual factors and clinical context when interpreting pressure measurements.
- Normal CSF pressure is common in patients with SIH, and the absence of a low opening pressure should not exclude this condition 4.
- The use of acetazolamide, a carbonic anhydrase inhibitor, is effective in treating idiopathic intracranial hypertension (IIH) by decreasing CSF fluid secretion and controlling intracranial pressure 5, 6.