A novel approach to CSF pressure measurement via lumbar puncture that shortens the measurement time with a high level of accuracy

Abstract

Intracranial pressure (ICP) is an important parameter in clinical management and diagnosis of several neurological diseases which is indirectly measured via lumbar puncture (LP). In routine measurements of cerebrospinal fluid pressure (P_CSF) from lumbar region, a spinal needle and a spinal manometer are used. P_CSF measurement via LP with the use of a spinal manometer may not yield correct P_CSF results due to prolonged times required to obtain an accurate pressure value. Equilibrium pressure may be underestimated in circumstances where spinal manometry procedure is terminated prematurely, with the wrong assumption that equilibrium pressure is reached. Elevated P_CSF levels can lead to visual loss and brain damage when go undiagnosed. In this study, the spinal needle-spinal manometer combination was modelled with a first-order differential equation and a time constant (τ) was defined as the product of the resistance to flow of the needle with the bore area of the manometer divided by the dynamic viscosity of CSF, i.e. τ= RA/ρ_CSF. Each needle/manometer combination had a unique constant as a predictor of the equilibrium pressure. The fluid pressure in the manometer rose in an exponential manner which was tested in a simulated environment using 22G spinal needles namely Braun-Spinocan, Pajunk-Sprotte and M.Schilling. Curve fitting of the manometer readings were obtained with regression coefficients of R² ≥ 0.99 to determine measurement time constants. The residual differences between predicted and true values were less than 1.18 cmH₂O. For a given needle/manometer combination, time required to reach equilibrium pressure was identical for all pressure levels. P_CSF measured at reduced times can easily be interpolated to their equilibrium level allowing clinicians to obtain P_CSF values with high accuracy within seconds. This method can be used as an indirect estimation of ICP in routine clinical practice.

Keywords: Cerebrospinal fluid pressure; Diagnostic lumbar puncture; Neurological diseases; Spinal manometer; Spinal needle; Time constant.