Hydrodynamic properties of the Certas hydrocephalus shunt

Laboratory investigation

Restricted access

Object

Independent testing of hydrocephalus shunts provides information about the quality of CSF drainage after shunt implantation. Moreover, hydrodynamic parameters of a valve assessed in the laboratory create a comparative pattern for testing of shunt performance in vivo. This study sought to assess the hydrodynamic parameters of the Certas valve, a new model of a hydrocephalus shunt.

Methods

The Certas valve is an adjustable ball-on-spring hydrocephalus valve. It can be adjusted magnetically in vivo in 7 steps, equally distributed within the therapeutic limit for hydrocephalus, and the eighth step at high pressures intended to block CSF drainage. The magnetically adjustable rotor is designed to prevent accidental readjustment of the valve in a magnetic field, including clinical MRI.

Results

The pressure-flow performance curves, as well as the operating, opening, and closing pressures, were stable, fell within the specified limits, and changed according to the adjusted performance levels. The valve at settings 1–7 demonstrated low hydrodynamic resistance of 1.4 mm Hg/ml/min, increasing to 5.1 mm Hg/ml/min after connection of a distal drain provided by the manufacturer. At performance Level 8 the hydrodynamic resistance was greater than 20 mm Hg/ml/min. External programming of the valve proved to be easy and reliable. The valve is safe in 3-T MRI and the performance level of the valve is unlikely to be changed. However, with the valve implanted, distortion of the image is substantial. Integration of the valve with the SiphonGuard limits the drainage rate.

Conclusions

In the laboratory the Certas valve appears to be a reliable differential-pressure adjustable valve. Laboratory evaluation should be supplemented by results of a clinical audit in the future.

Abbreviations used in this paper:ICP = intracranial pressure; ISO = International Organization for Standardization; NPH = normal-pressure hydrocephalus; UK = United Kingdom.

Article Information

Address correspondence to: Marek Czosnyka, Ph.D., Neurosurgical Unit, Box 167, Addenbrooke's Hospital, Cambridge, United Kingdom CB2 0QQ. email: mc141@medschl.cam.ac.uk.

Please include this information when citing this paper: published online December 7, 2012; DOI: 10.3171/2012.10.PEDS12239.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Schematic diagram of the construction of the Certas valve. This figure was scanned from the leaflet provided by the manufacturer.

  • View in gallery

    Schematic diagram of the shunt testing apparatus (see Methods section in text for description).

  • View in gallery

    Pressure-flow performance curves of a valve at a fixed pressure level. A: Individual pressure-flow curve for the Certas valve set at performance Level 4. B: Summary of pressure-flow curves after 10 tests. C: Pressure-flow curves without (left) and with (right) a distal drain. D: Pressure-flow curve of the valve with SiphonGuard, with the valve set at performance Level 3. Arrows show the direction of change of flow through the shunt system.

  • View in gallery

    Graphs showing the group of pressure-flow curves for different performance levels (upper), and mean values, 95% CIs (vertical bars), and ranges (horizontal bars) for the valve's operating pressure at different performance levels (lower).

  • View in gallery

    Distortion of an MR image by a Certas valve in a water-filled container, with a diameter equivalent to an adult skull. Upper: Gradient echo image. Lower: Spin echo image.

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