In vivo intracranial pressure dynamics in patients with hydrocephalus treated by shunt placement

Object. With the commercial availability of a variety of shunt systems, the re is considerable controversy over the choice of the most appropriate shun t valve for each individual with hydrocephalus. Although the performance ch aracteristics of all shunt systems are well documented in the laboratory se tting, there is little description of the in vivo dynamics of intracranial pressure (ICP) after implantation of commonly used shunt systems in humans. The authors coupled telemonitoring devices to several different shunt syst ems to measure the performance characteristics of these valve systems with respect to intraventricular pressure (IVP) at increments of head elevation. Methods. Twenty-five patients with different shunt systems and three contro l patients without shunts were studied for IVP at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees of head elevat ion, and the resultant curves were analyzed for the best-fit regression coe fficient. For purposes of analysis the authors grouped shunt valve systems by design characteristics into three groups: differential-pressure valves ( r = -0.321 +/- 0.061; 11 patients), nonsiphoning systems (r = -0.158 +/- 0. 027; 10 patients), and flow-regulated valves (r = -0.16 +/- 0.056; four pat ients);there were three control patients without shunts (r = -0.112 +/- 0.0 37). Conclusions. The authors found that differential-pressure valves always cau sed ICP to drop to 0 by 30 degrees of head elevation, whereas all other val ve systems caused a more gradual drop in ICP, more consistent with pressure s observed in the control patients without shunts. Not surprisingly, the di fferential-pressure valve group was found to have a significant difference in mean regression coefficient when compared with those in whom nonsiphonin g shunts (p < 0.023) or no shunts were placed (p < 0.049). These data provi de a basis for evaluating shunt valve performance and for predicting valve appropriateness in patients in whom characteristics such as pressure and fl ow dynamics are weighed in the choice of a specific valve for implantation.