Telemetric assessment of intracranial pressure changes consequent to manipulations of the Codman-Medos programmable shunt valve

Introduction: Noninvasive manipulation of programmable shunt valves may all ow customization of intracranial pressure (ICP) dynamics in individual shun ted patients. Manipulations of the recently FDA-approved Codman-Medos varia ble pressure valve (VPV) are monitored by radiographic changes in the valve mechanism, necessitating a skull radiograph with each pressure change. We wished to assess the in vivo impact of VPV manipulations on ICP changes usi ng a noninvasive telemonitor as an alternative to radiographic confirmation and as a method for validating the ICP changes. Methods: Tele-Sensor devic es (Radionics) were implanted in-line with 12 VPV shunt systems. ICP was as sessed telemetrically in the supine position whenever the valve pressure wa s adjusted (both before and 2-5 min after the manipulation). Results: Valve manipulation was confirmed by radiograph for the initial manipulations onl y and matched the telemetric pressure changes observed in all cases, Confir med manipulations of the valve were generally followed by a near equivalent relative change in ICP (less than or equal to 2 cm difference 74% of the t ime); however, the absolute value of the supine ICP was dependent on the en tire shunting system and was equivalent to the valve setting only 11% of th e time. Supine ICP and ICP dynamics were also dependent more on the shunt s ystem than simply on the valve setting and were different for each of the s hunt systems tested. Conclusions: We have confirmed that the VPV does cause ICP changes in shunted hydrocephalic patients that are essentially equival ent to programmed relative changes in the valve settings. These changes can be as easily monitored by noninvasive telemetry as by repeated radiography . However, our observations demonstrate that additional factors in the shun ting system render the ICP absolutely equivalent to the VPV setting only ra rely, implying that a programmable shunt valve is not necessarily equivalen t to programmable ICP. Copyright (C) 2001 S. Karger AG, Basel.