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

INTRODUCTION

Noninvasive manipulation of programmable shunt valves may allow customization of intracranial pressure (ICP) dynamics in individual shunted patients. Manipulations of the recently FDA-approved Codman-Medos variable 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 using a noninvasive telemonitor as an alternative to radiographic confirmation and as a method for validating the ICP changes.

METHODS

TeleSensor devices (Radionics) were implanted in-line with 12 VPV shunt systems. ICP was assessed telemetrically in the supine position whenever the valve pressure was adjusted (both before and 2-5 min after the manipulation).

RESULTS

Valve manipulation was confirmed by radiograph for the initial manipulations only and matched the telemetric pressure changes observed in all cases. Confirmed manipulations of the valve were generally followed by a near equivalent relative change in ICP (</=2 cm difference 74% of the time); however, the absolute value of the supine ICP was dependent on the entire shunting system and was equivalent to the valve setting only 11% of the time. Supine ICP and ICP dynamics were also dependent more on the shunt system than simply on the valve setting and were different for each of the shunt systems tested.

CONCLUSIONS

We have confirmed that the VPV does cause ICP changes in shunted hydrocephalic patients that are essentially equivalent 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 shunting system render the ICP absolutely equivalent to the VPV setting only rarely, implying that a programmable shunt valve is not necessarily equivalent to programmable ICP.