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Which shunt adjustment to select for normal pressure hydrocephalus remains a matter of controversy. While many patients do benefit from medium pressure adjustments, some might need ultralow pressure setting to experience satisfying results. In this issue, an article addressing the difficult adjustment of shunts in normal pressure hydrocephalus patients is presented.
When it comes to the details of shunt valve settings, there is a wide range of options to choose from:
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Shall we implant valves regulated by CSF flow or rather use valves regulated by intracranial pressure?
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Shall we use a single differential pressure valve or is a combination with an anti-siphon device (ASD) preferable?
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Shall we opt for valves with a fixed pressure setting or implant valves with an option to adjust the pressure or shall we even implant a combination of fixed pressure valves and adjustable valves?
The application of flow-regulated versus differential pressure-regulated valves in patients with NPH has not been investigated by randomized clinical trials yet [17]. Recently, a study group published two studies about its retrospectively collected data with interesting results concerning outcome and complication rate [14]. Another publication of the same group showed that the use of flow-regulated valves may be comparable with the use of differential pressure valves [15].
It was also demonstrated that the frequency of overdrainage in the flow-regulated group was lower than in the differential pressure valve group. However, it is important to note that no ASD was used, which would have reduced the rate of overdrainage significantly [2, 6, 12].
Generally, there exists substantial data supporting the fact that when a differential pressure valve is used, it should be done in combination with an ASD, since it has been shown repeatedly that this combination is superior to the stand-alone technique. ASD decreases the rate of overdrainage and does not increase the rate of underdrainage [2, 6, 12].
In cases where because of cost factors only one valve can be used, existing data suggests that it may be advisable to use only an ASD instead of a differential pressure valve [5, 11].
The decision between programmable and fixed devices seemed to be clear—the safety and efficiency of programmable valves have been published in several studies [5, 6, 12, 16].
Having the option to adapt the opening pressure is obviously favorable to treat complications like overdrainage and to optimize the outcome [4, 8, 13, 16].
But even after having made all of these decisions above on what valve to use, the question what is the optimal opening pressure for a patient with NPH still remains—and it is not easy to answer.
Overall, low opening pressures seemed to be favorable for the functional outcome of the NPH patient [1, 3, 7, 9], especially when the shunt system included an ASD for prevention from underdrainage [3, 7]. Furthermore, the stepwise lowering of the opening pressure could possibly be favorable [1, 4]. Therefore, programmable valves in combination with an ASD seems to be the optimal choice.
But there is more. In the following study by Funell et al., a cohort of NPH patients with a low-pressure-state NPH is presented. These patients underwent surgery for replacing a fixed ASD with a programmable ASD (proSA). With this adjustable device, the study group attains a treatment option in this subtype of NPH.
In their conclusion—and the authors of this editorial are in consent with this, they suggest for cases of complex hydrocephalus like the NPH a combination of a programmable differential and anti-gravity valve.
At present, clinical data about this valve combination are rare. Mansson et al. show the benefit of such a system in complex shunted patients [8]. The recently started SYGRAVA study will evaluate whether programmable anti-siphon devices compared with fixed anti-siphon devices are able to avoid both over- and underdrainage complications [10].
At present, the combination of adjustable differential pressure and adjustable anti-gravity valves is used especially in patients with complex hydrocephalus and CSF-associated diseases when optimum adjustment is needed. In these, it is a very feasible technique. But more data are to come to further refine indication and settings in this subgroup of patients.
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Oertel, J.M.K., Huelser, M.J.M. Is there an ideal shunt valve and opening pressure setting for NPH?. Acta Neurochir 162, 2965–2966 (2020). https://doi.org/10.1007/s00701-020-04598-x
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DOI: https://doi.org/10.1007/s00701-020-04598-x