Laboratory evaluation of the phoenix CRx diamond valve

Antisiphon device: a review of existing mechanisms and clinical applications to prevent overdrainage in shunted hydrocephalic patients

Overdrainage of cerebrospinal fluid is one of the most notorious complications after ventriculoperitoneal shunt implantation. Siphon effect plays a major role in the development of overdrainage. Various overdrainage-preventing devices have been invented to counteract the siphon effect. Though some of the devices are designed to reduce the flow instead of providing antisiphoning effect, they are generally called antisiphon devices (ASDs). The basics of siphoning, the mechanisms and physical properties of currently available devices are described in this article. The clinical efficacy, shunt survival, and considerations on patient factors are also discussed. There are three kinds of ASD design, diaphragm, gravitational, and flow reducing devices. Flow reducing ASD is always open and the flow it controls is relatively stable. On the other hand, it may not provide sufficient flow in nocturnal intracranial pressure elevations. Diaphragm and gravitational devices are sensitive to the position of the patients. Diaphragm device is sensitive to the external pressure and the relative position of the device to the mastoid process. The gravitational device is sensitive to the angle between the axis of the device and the head. Many studies showed encouraging results with gravitational devices. Studies regarding diaphragm devices either showed better or similar outcomes comparing to differential pressure valves. Clinical studies regarding flow-reducing devices and head-to-head comparison between different mechanisms are warranted. This review aims to provide a useful reference for clinical practice of hydrocephalus.

CSF Dynamics for Shunt Prognostication and Revision in Normal Pressure Hydrocephalus

BACKGROUND

Despite the quantitative information derived from testing of the CSF circulation, there is still no consensus on what the best approach could be in defining criteria for shunting and predicting response to CSF diversion in normal pressure hydrocephalus (NPH).

OBJECTIVE

We aimed to review the lessons learned from assessment of CSF dynamics in our center and summarize our findings to date. We have focused on reporting the objective perspective of CSF dynamics testing, without further inferences to individual patient management.

DISCUSSION

No single parameter from the CSF infusion study has so far been able to serve as an unquestionable outcome predictor. Resistance to CSF outflow (Rout) is an important biological marker of CSF circulation. It should not, however, be used as a single predictor for improvement after shunting. Testing of CSF dynamics provides information on hydrodynamic properties of the cerebrospinal compartment: the system which is being modified by a shunt. Our experience of nearly 30 years of studying CSF dynamics in patients requiring shunting and/or shunt revision, combined with all the recent progress made in producing evidence on the clinical utility of CSF dynamics, has led to reconsidering the relationship between CSF circulation testing and clinical improvement.

CONCLUSIONS

Despite many open questions and limitations, testing of CSF dynamics provides unique perspectives for the clinician. We have found value in understanding shunt function and potentially shunt response through shunt testing in vivo. In the absence of infusion tests, further methods that provide a clear description of the pre and post-shunting CSF circulation, and potentially cerebral blood flow, should be developed and adapted to the bed-space.

How to Choose a Shunt for Patients with Normal Pressure Hydrocephalus: A Short Guide to Selecting the Best Shunt Assembly

Most patients with hydrocephalus are still managed with the implantation of a cerebrospinal fluid (CSF) shunt in which the CSF flow is regulated by a differential-pressure valve (DPV). Our aim in this review is to discuss some basic concepts in fluid mechanics that are frequently ignored but that should be understood by neurosurgeons to enable them to choose the most adequate shunt for each patient. We will present data, some of which is not provided by manufacturers, which may help neurosurgeons in selecting the most appropriate shunt. To do so, we focused on the management of patients with idiopathic “normal-pressure hydrocephalus” (iNPH), as one of the most challenging scenarios, in which the combination of optimal technology, patient characteristics, and knowledge of fluid mechanics can significantly modify the surgical results. For a better understanding of the available hardware and its evolution over time, we will have a second look at the design of the first DPV and the reasons why additional devices were incorporated to control for shunt overdrainage and its related complications. We try to persuade the reader that a clear understanding of the physical concepts of the CSF and shunt dynamics is key to understand the pathophysiology of iNPH and to improve its treatment.

A Review of Passive Constant Flow Regulators for Microfluidic Applications

This review gives an overview of passive constant flow regulators dedicated to microfluidic applications. Without external control and energy consumption, these devices deliver a constant flow rate regardless of pressure variations, making them very attractive for various microfluidic applications, including drug delivery, flow chemistry, point-of-care tests, or microdialysis. This technical review examines progress over the last three decades in the development of these flow regulators and focuses on the working principle, fabrication methods, performance, and potential applications.

Shunt survival rates by using the adjustable differential pressure valve combined with a gravitational unit (proGAV) in pediatric neurosurgery

OBJECT

Overdrainage is a chronic complication in shunted pediatric patients with hydrocephalus. The use of adjustability of differential pressure (DP) valves in combination with antisiphoning devices may help to overcome this sequela and may diminish the rate of possible shunt failures. The purpose of this retrospective study is to report our experience on shunt survival and infection rate with an adjustable DP valve with integrated gravitational unit in pediatric hydrocephalus.

METHODS

The proGAV consists of an adjustable differential pressure (DP) valve and a gravitational unit. During the time period of July 2004 and December 2009, a total of 237 adjustable gravitational valves were used in 203 children (age, 6.5 ± 6.54; 0-27 years). In the follow-up period, valve and shunt failures as well as rate of infection were recorded.

RESULTS

Within the average follow-up time of 21.9 ± 10.3 months (range, 6-72 months), the valve survival rate was 83.8 %. The overall shunt survival rate including all necessary revisions was 64.3 %. Looking at the group of infants (<1 year of age) within the cohort, the valve survival rate was 77.3 % and the shunt survival rate was 60.9 %. The overall infection rate was 4.6 %.

CONCLUSION

In a concept of avoiding chronic overdrainage by using the proGAV in hydrocephalic children, we observed a good rate of valve and shunt survival. Compared to previous reported series, we experienced the proGAV as a reliable tool for the treatment of pediatric hydrocephalus.

Effect of transcranial magnetic stimulation on four types of pressure-programmable valves

BACKGROUND

Exposure to powerful magnetic fields may alter the settings of programmable ventriculoperitoneal shunt valves or even cause permanent damage to these devices. Transcranial magnetic stimulation (TMS) and magnetic resonance imaging both generate a high-intensity, focal magnetic field. To the best of our knowledge, there is no literature data on the compatibility of TMS with neurosurgical implants. The aim of the present in vitro study was to investigate the effects of TMS on four types of pressure-programmable valves (the Strata 2 from Medtronic, the Polaris from Sophysa, the ProGAV from Miethke, and a cylindrical valve from Codman-Hakim).

METHODS

We used a Magpro X100 stimulator (Medtronic) for monophasic or biphasic TMS via a circular or a figure-of-eight coil. Each valve setting was tested before and after exposure to TMS. Experiment 1: The effect of the coil-valve distance (10, 5, 2.5, and 1 cm) was assessed. Experiment 2: We mimicked in situ stimulation with a human mannequin by placing the valve in a retroauricular position, the TMS circular coil on the apex, and figure-of-eight coil centered over the primary motor area site. Temperature changes were monitored throughout the experiments. Experience 3: TMS-induced valve movements were assessed by using an in-house accelerometric setup.

RESULTS

Our results primarily demonstrated that the Strata 2 and Codman-Hakim valves' settings were perturbed by TMS. There was no heating effect for any of the valves. However, TMS induced movements of the Strata 2, Polaris, and ProGAV valves. Experiment 1: The unsetting frequencies observed for the Strata 2 and the Codman-Hakim valve showed an influence of the distance, the coil model, and the magnetic field characteristics, whereas the Polaris and ProGAV's settings remained unchanged. Experiment 2: Unsetting occurred for Strata 2 valve with the circular coil only, whereas the Polaris, ProGAV, and Codman-Hakim valves' settings remained stable. Experiment 3: The Strata 2, Polaris, and ProGAV valves showed high-amplitude oscillations during TMS under all stimulation conditions, whereas the Codman-Hakim valve did not move.

CONCLUSIONS

Our in vitro experiments showed that TMS can interfere with programmable shunt valves by inducing unsetting or movement. This finding suggests that great care must be taken if applying TMS in hydrocephalic, shunted patients.

Investigation of the hydrodynamic properties of a new MRI-resistant programmable hydrocephalus shunt

Background

The Polaris valve is a newly released hydrocephalus shunt that is designed to drain cerebrospinal fluid (CSF) from the brain ventricles or lumbar CSF space. The aim of this study was to bench test the properties of the Polaris shunt, independently of the manufacturer.

Methods

The Polaris Valve is a ball-on-spring valve, which can be adjusted magnetically in vivo. A special mechanism is incorporated to prevent accidental re-adjustment by an external magnetic field. The performance and hydrodynamic properties of the valve were evaluated in the UK Shunt Evaluation Laboratory, Cambridge, UK.

Results

The three shunts tested showed good mechanical durability over the 3-month period of testing, and a stable hydrodynamic performance over 45 days. The pressure-flow performance curves, operating, opening and closing pressures were stable. The drainage rate of the shunt increased when a negative outlet pressure (siphoning) was applied. The hydrodynamic parameters fell within the limits specified by the manufacturer and changed according to the five programmed performance levels. Hydrodynamic resistance was dependant on operating pressure, changing from low values of 1.6 mmHg/ml/min at the lowest level to 11.2 mmHg/ml/min at the highest performance level. External programming proved to be easy and reliable. Even very strong magnetic fields (3 Tesla) were not able to change the programming of the valve. However, distortion of magnetic resonance images was present.

Conclusion

The Polaris Valve is a reliable, adjustable valve. Unlike other adjustable valves (except the Miethke ProGAV valve), the Polaris cannot be accidentally re-adjusted by an external magnetic field.

Treatment of hydrocephalus determined by the European Orbis Sigma Valve II survey: a multicenter prospective 5-year shunt survival study in children and adults in whom a flow-regulating shunt was used

OBJECT

The goal of this study was to evaluate the long-term results of a flow-regulating shunt (Orbis Sigma Valve [OSV] II Smart Valve System; Integra NeuroSciences, Sophia Antipolis, France) in the treatment of hydrocephalus, whether it was a first insertion procedure or surgical revision of another type of shunt, in everyday clinical practice in a multicenter prospective study.

METHODS

Patients of any age who had hydrocephalus underwent implantation of an OSV II system. The primary end point of the study was defined as any shunt-related surgery. The secondary end point was a mechanical complication (shunt obstruction, overdrainage, catheter misplacement, migration, or disconnection) or infection. The overall 5-year shunt survival rates and survival as it applied to different patient subgroups were assessed. Five hundred fifty-seven patients (48% of whom were adults and 52% of whom were children) were selected for OSV II shunt implantation; 196 patients reached the primary end point. Shunt obstruction occurred in 75 patients (13.5%), overdrainage in 10 patients (1.8%), and infection in 46 patients (8.2%). The probability of having experienced a shunt failure-free interval at 1 year was 71% and at 2 years it was 67%; thereafter the probability remained quite stable in following years (62% at the 5-year follow-up examination). No difference in shunt survival was observed between the overall pediatric (< or = 16 years of age) and adult populations. In the pediatric age group, however, there was a significantly lower rate of shunt survival in children younger than 6 months of age (55% at the 5-year follow-up examination).

CONCLUSIONS

In this prospective study the authors demonstrate the effectiveness of flow regulation in the treatment of hydrocephalus both in children and in adults. Flow-regulating shunts limit the incidence of overdrainage and shunt-related complications. The overall 5-year shunt survival rate (62%) compares favorably with rates cited in other recently published series.