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

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Abstract
With the commercial availability of a variety of shunt systems, there is considerable controversy over the choice of the most appropriate shunt valve for each individual with hydrocephalus. Although the performance characteristics of all shunt systems are well documented in the laboratory setting, 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 systems to measure the performance characteristics of these valve systems with respect to intraventricular pressure (IVP) at increments of head elevation. Twenty-five patients with different shunt systems and three control 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 elevation, and the resultant curves were analyzed for the best-fit regression coefficient. 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 patients); there were three control patients without shunts (r = -0.112 +/- 0.037). The authors found that differential-pressure valves always caused ICP to drop to 0 by 30 degrees of head elevation, whereas all other valve systems caused a more gradual drop in ICP, more consistent with pressures observed in the control patients without shunts. Not surprisingly, the differential-pressure valve group was found to have a significant difference in mean regression coefficient when compared with those in whom nonsiphoning shunts (p < 0.023) or no shunts were placed (p < 0.049). These data provide a basis for evaluating shunt valve performance and for predicting valve appropriateness in patients in whom characteristics such as pressure and flow dynamics are weighed in the choice of a specific valve for implantation.