Assessment of cerebrospinal fluid outflow conductance using constant-pressure infusion—a method with real time estimation of reliability

Abstract

The outflow conductance (Cout) of the cerebrospinal fluid (CSF) system is a parameter considered to be predictive in selection for hydrocephalus surgery. Cout can be determined through an infusion test. A new apparatus for performing infusion tests in a standardized and automated way was developed. The objective was to evaluate repetitiveness as well as to propose and evaluate a method for real time estimation of the reliability of individual Cout investigations. Repeated investigations were performed on an experimental model simulating the CSF system, and on 14 patients with hydrocephalus. ΔCout, calculated as the 95% confidence interval of Cout, was introduced as an estimate of the reliability of individual Cout investigations. On the model, no significant difference was found between ΔCout and the actual Cout variation in repeated investigations (p = 0.135). The correlation between the first and the second patient investigation was high (R = 0.99, p < 0.05), although there was a significant difference between the investigations (p < 0.05). The standard deviation of difference was 2.60 µl (s kPa)−1. The repetitiveness of Cout with the new apparatus was high, and ΔCout reflected the reliability of each investigation. This feature has to be taken into account in every individual case, before making a decision or performing research based on measurements of Cout in the future.