How does intrathecal pressure measured in the sitting position by lumbar puncture (LP) correlate to intracranial pressure (ICP) measured by external ventricular drainage (EVD)?

From the Guidelines

Intrathecal pressure measured in sitting position by lumbar puncture does not accurately correlate with intracranial pressure (ICP) measured by external ventricular drainage (EVD). The sitting position creates a hydrostatic pressure gradient that artificially lowers the lumbar pressure reading compared to the actual ICP, as noted in guidelines for managing spontaneous intracerebral hemorrhage 1. For accurate ICP assessment, lumbar puncture should be performed in the lateral recumbent position, which better correlates with EVD measurements, though still with limitations. Even in the lateral position, lumbar pressure may not reflect true ICP in cases of obstructed CSF flow, such as with brain tumors, hydrocephalus, or other mass lesions. EVD remains the gold standard for ICP monitoring as it provides direct measurement from the ventricular system. The pressure gradient exists because the cerebrospinal fluid system functions as a continuous column of fluid, and in the sitting position, gravity pulls the fluid downward, creating lower pressure readings at the cranial level and higher readings at the lumbar level. This hydrostatic effect can lead to significant measurement discrepancies, potentially missing elevated ICP if relying solely on sitting lumbar puncture readings.

Some key points to consider when measuring ICP include:

• The method of measurement: EVD is considered the gold standard for ICP monitoring 1
• The position of the patient during measurement: lateral recumbent position is preferred over sitting position
• The potential for obstructed CSF flow: brain tumors, hydrocephalus, or other mass lesions can affect the accuracy of lumbar pressure readings
• The risks associated with ICP monitoring: infection and intracranial hemorrhage are potential complications, with higher risks associated with ventricular catheters compared to parenchymal catheters 1.

Given the potential for significant measurement discrepancies and the limitations of lumbar puncture in certain cases, EVD should be used for accurate ICP measurement, especially in patients with suspected elevated ICP or those requiring close monitoring of ICP. The decision to use a VC or a parenchymal catheter device should be based on the specific need to drain CSF in patients with hydrocephalus or “trapped ventricle” and the balance of monitoring risks with the unknown utility of ICP management in patients with ICH 1.

From the Research

Correlation Between Intrathecal Pressure and ICP Pressure

• The correlation between intrathecal pressure measured in a sitting position by lumbar puncture and ICP pressure measured by external ventricular drainage is not directly addressed in the provided studies 2, 3, 4, 5, 6.
• However, studies have investigated the use of lumbar drainage in managing elevated intracranial pressure, which may provide some insight into the relationship between intrathecal pressure and ICP pressure.
• A study by 4 found that controlled lumbar drainage can reduce ICP in patients with medically refractory increased intracranial pressure, suggesting a potential correlation between intrathecal pressure and ICP pressure.
• Another study by 6 found that external lumbar drainage has a significant immediate effect on ICP, with a pooled effect size of -19.5 mmHg, which may indicate a correlation between intrathecal pressure and ICP pressure.

Measurement and Management of ICP

• ICP is typically measured using invasive methods such as ventriculostomy or external ventricular drainage 2, 3.
• The management of elevated ICP involves a range of therapeutic interventions, including decompressive surgery, osmotherapy, hyperventilation, and pharmacological interventions 3, 5.
• Lumbar drainage has been shown to be a safe and effective treatment for elevated ICP refractory to medical management 4, 6.

Limitations and Future Directions

• The provided studies do not directly address the correlation between intrathecal pressure measured in a sitting position by lumbar puncture and ICP pressure measured by external ventricular drainage.
• Further research is needed to investigate the relationship between intrathecal pressure and ICP pressure, as well as the optimal management strategies for elevated ICP 5, 6.