Comparison between 3 infusion methods to measure cerebrospinal fluid outflow conductance Clinical article

Object. There are several infusion methods available to estimate the outflow conductance (C-out) or outflow resistance (R-out= 1/C-out) of the CSF system. It has been stated that for unknown reasons, the bolus infusion method estimates a higher C-out than steady-state infusion methods. The aim of this study was to compare different infusion methods for estimation of C-out. Methods. The following 3 different infusion methods were used: the bolus infusion method (C-out bol); the constant flow infusion method, both static (C-out stat) and dynamic (C-out dyn) analyses; and the constant pressure infusion method (C-out cpi). Repeated investigations were performed on an experimental model with well-known characteristics, with and without physiological pressure variations (B-waves, breathing, and so on). All 3 methods were also performed in a randomized order during the same investigation in 20 patients with probable or possible idiopathic normal-pressure hydrocephalus: 6 of these patients had a shunt and 14 did not. Results. Without the presence of physiological pressure variations, the concordance in the experimental model was good between all methods. When they were added, the repeatability was better for the steady-state methods and a significantly higher C-out was found with the bolus method in the region of clinically relevant C-out (p < 0.05). The visual fit for the bolus infusion was dependent on subjective assessment by the operator. This experimental finding was confirmed by the clinical results, where significant differences were found in the investigations in patients without shunts between C-out of the visual bolus method and C-out (stat), C-out dyn, and C-out cpi (4.58, 4.18, and 6.12 mu l/[second x kPa], respectively). Conclusions. This study emphasized the necessity for standardization of C-out measurements. An experienced operator could partly compensate for difficulties in correctly estimating the pressure parameters for the bolus infusion method, but for the general user this study suggests a steady-state method for estimating C-out. (DOI: 10.3171/2010.8.JNS10157)