Summary
Background
We have previously reported that the intracranial pulse pressure amplitudes were elevated in idiopathic normal pressure hydrocephalus (NPH) patients responding to shunt surgery. Whether or not shunt implantation or adjustment of the shunt valve opening pressure modifies the intracranial pulse pressure amplitudes in NPH patients remains to be established. This report summarises our observations.
Patients and methods
Thirteen patients with NPH (idiopathic in nine and secondary in four) are presented in whom continuous intracranial pressure (ICP) monitoring was done before and after shunt implantation. In two, ICP monitoring was also done during adjustment of shunt valve opening pressure. The mean ICP and mean ICP wave amplitude (i.e. pulse pressure amplitudes) were determined in 6-s time windows.
Results
After shunt implantation there was a fall in both mean ICP and mean ICP wave amplitude; the reduction in the two ICP parameters correlated significantly. However, mean ICP in the supine position was normal (i.e. <15 mmHg) in 12 of 13 patients before shunt placement, and remained normal after shunting. According to our criteria, the mean ICP wave amplitudes were elevated before shunting in 12 of 13 patients and became “normalised” the day after shunting in nine patients. The reduction in mean ICP wave amplitude after shunt was highly significant at the group level. Moreover, adjustment of shunt valve opening pressure modified the levels of mean ICP wave amplitudes.
Conclusions
The present observations in 13 NPH patients indicate that shunt implantation reduces mean ICP wave amplitudes. Moreover, the level of reduction can be tailored by adjustment of the shunt valve opening pressure.
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This paper describes further work from this group on the puslatility of the ICP waveform in patients who either have, or may benefit from, a shunt.
Previously they have shown that higher ICP pulse pressure amplitudes may be a useful index for positive shunt response.
This study addressed the question of whether shunt implantation reduces pre- pulse pressure amplitude. Although the numbers in this study are small this does appear to the case even whilst the mean value of ICP remained within normal range throughout.
This methodology appears to give useful clinical information. In comparison to other methods, such as B wave analysis, implementation is simpler and therefore there may be greater potential to have such monitoring and analysis in real time at the bedside.
As the authors point out the goal of finding the optimal shunt valve opening pressure is still elusive. The production of intelligent shunts where not only the opening pressure can be altered but also the ICP waveform externally measured and monitored should improve the way patients with hydrocephalus are managed.
Iain Chambers
The James Cook University Hospital
ICP monitoring and measurement of the mean ICP wave amplitude was performed in 13 patients with Normal Pressure Hydrocephalus before and one day after shunting. As one would expect shunting resulted in a reduction of both ICP and ICP wave amplitude. No relation was found, however, with clinical improvement. As clinical improvement may take weeks or months such a relation was not very likely. Therefore, leaving a pressure transducer inside one day after shunting does not seem useful in clinical practise.More interesting were the results of measuring ICP and wave amplitude during adjustments of the valve opening pressure. By gradual lowering of this opening pressure first a reduction of both parameters was seen later followed by diverging changes of mean ICP and mean ICP wave amplitude permitting fine tuning of the valve opening pressure and clinical improvement. Here the availability of continuous online data is advantage compared to measurement of CSF outflow resistance by an infusion test.
Jos Th J Tans
Medical Center Haaglanden, The Hague
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Eide, P.K., Sorteberg, W. Changes in intracranial pulse pressure amplitudes after shunt implantation and adjustment of shunt valve opening pressure in normal pressure hydrocephalus. Acta Neurochir (Wien) 150, 1141–1147 (2008). https://doi.org/10.1007/s00701-008-0138-8
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DOI: https://doi.org/10.1007/s00701-008-0138-8