Shunt Technology Research Articles

Impedance Changes Indicate Proximal Ventriculoperitoneal Shunt Obstruction In Vitro.

Extracranial cerebrospinal fluid (CSF) shunt obstruction is one of the most important problems in hydrocephalus patient management. Despite ongoing research into better shunt design, robust and reliable detection of shunt malfunction remains elusive. The authors present a novel method of correlating degree of tissue ingrowth into ventricular CSF drainage catheters with internal electrical impedance. The impedance based sensor is able to continuously monitor shunt patency using intraluminal electrodes. Prototype obstruction sensors were fabricated for in-vitro analysis of cellular ingrowth into a shunt under static and dynamic flow conditions. Primary astrocyte cell lines and C6 glioma cells were allowed to proliferate up to 7days within a shunt catheter and the impedance waveform was observed. During cell ingrowth a significant change in the peak-to-peak voltage signal as well as the root-mean-square voltage level was observed, allowing the impedance sensor to potentially anticipate shunt malfunction long before it affects fluid drainage. Finite element modeling was employed to demonstrate that the electrical signal used to monitor tissue ingrowth is contained inside the catheter lumen and does not endanger tissue surrounding the shunt. These results may herald the development of "next generation" shunt technology that allows prediction of malfunction before it affects patient outcome.

Ventriculoperitoneal Shunt 30-Day Failure Rate

With the need for transparency of surgical results, 30-day outcome measures have become increasingly important. Ventriculoperitoneal (VP) shunt failure is a substantial burden to patients and health care systems. This study introduces the 30-day VP shunt failure rate as a possible barometer of surgical outcome and demonstrates its use in a national (United Kingdom [UK]) study and makes comparison with 2 published randomized, controlled trials (RCT). A cohort study of all (except 1) pediatric neurosurgical centers in the UK and Ireland. All new and revision VP shunt operations were recorded for 2008 and 2009. Both newly placed and revised VP shunts were subject to Kaplan-Meier analysis, and 30-day failure rate was obtained. Data from 2 RCTs investigating new VP shunt technology were analyzed, and the 30-day failure rate was extracted for comparative purposes. The overall 30-day and 1-year failure rates for new shunts were 12.9% and 28.8%, respectively. The 30-day failure rate from 2 RCTs was comparable (14% and 16%, respectively). The failure rate of the subsequent revision of those new shunts was 20.7% at 30 days and 40.4% at 1 year. According to these data, shunt survival appears to be better if performed by a consultant pediatric neurosurgeon for revision surgery only. VP shunt survival in the UK is comparable to the published multicenter data investigating shunt survival. The 30-day failure rate may represent a better barometer of surgical outcome and should be used as a separate outcome measure in the design of future trials.

In-Vitro Evaluation of a Drainage Catheter with Integrated Bioimpedance Electrodes to Determine Ventricular Size

Patients suffering from Hydrocephalus show an increased accumulation of cerebrospinal fluid, which needs to be drained into another body compartment by an im- planted shunt. To prevent from over-drainage, which some- times still occurs despite improvements in shunt technology, a possible future shunt could contain sensors and supervise the ventricular size electrically. This work approaches this and presents the in vitro study of a drainage catheter with integrated bioimpedance evaluation capabilities.

Pre- and post-shunting observations in adult sheep with kaolin-induced hydrocephalus

BackgroundThe objective of this study was to examine host-shunt interactions in sheep with kaolin-induced hydrocephalus.MethodsForty-two sheep (29–40 kg) were utilized for this study. In 20 animals, various kaolin doses were injected into the cisterna magna including 10 and 50 mg/kg as well as 2–4 ml of a 25% kaolin suspension. Based on animal health and hydrocephalus development, 3 ml of a 25% kaolin suspension was chosen. In 16 animals, kaolin was administered and 6–8 days later, the animals received a custom made ventriculo-peritoneal shunt. In 8 animals ventricular CSF pressures were measured with a water manometer before kaolin administration and 7–8 days later. The sheep were allowed to survive for up to 9–12 weeks post-kaolin or until clinical status required euthanasia. Brains were assessed for morphological and histological changes. Ventricle/cerebrum cross sectional area ratios (V/C) were calculated from photographs of the sliced coronal planes immediately anterior to the interventricular foramina.ResultsIntraventricular pressures increased from 12.4±1.1 cm H2O to 41.3±3.5 cm H2O following kaolin injection (p < 0.0001, n = 8). In all animals, we observed kaolin on the basal surface of the brain and mild (V/C 0.03-0.10) to moderate (V/C >0.10) ventricular expansion. The animals lost weight between kaolin administration and shunting (33.7±1.2 kg versus 31.0±1.7 kg) with weights after shunting remaining stable up to sacrifice (31.6±2.2 kg). Of 16 shunted animals, 5 did well and were sacrificed 9–12 weeks post-kaolin. In the remainder, the study was terminated at various times due to deteriorating health. Hydrocephalus was associated with thinning of the corpus callosum, but no obvious loss of myelin staining, along with reactive astroglial (glial fibrillary acidic immunoreactive) and microglial (Iba1 immunoreactive) changes in the white matter. Ventricular shunts revealed choroid plexus ingrowth in 5/16, brain tissue ingrowth in 1/16, problems with shunt insertion in 3/16, occlusion by hemorrhagic-inflammatory material in 5/16, or no obstruction in 2/16. Free flowing CSF indicated that the peritoneal catheter was patent.ConclusionsCerebrospinal fluid shunts in hydrocephalic sheep fail in ways that are reminiscent of human neurosurgical experience suggesting that this model may be helpful in the development of more effective shunt technology.

Addressing the siphoning effect in new shunt designs by decoupling the activation pressure and the pressure gradient across the valve

Although several improvements have been observed in the past few years in shunt technology, currently available systems still present several associated problems. Among these, overdrainage along with its complications remains one of the great challenges for new shunt designs. To address the so-called siphoning effect, the authors provide a practical example of how it is possible to decouple the activation pressure and the pressure gradient across the valve through a 3-key component system. In this new shunt design, the flow is expected to depend only on the intracranial pressure and not on the pressure gradient across the valve, thus avoiding the so-called siphoning effect. The authors used computer models to theoretically evaluate the mechanical variables involved in the operation of the newly designed valve, such as the fluid's Reynolds number, proximal pressure, distal pressure, pressure gradient, actual flow rate, and expected flow rate. After fabrication of the first superscaled model, the authors performed benchmark tests to analyze the performance of the new shunt prototype, and the obtained data were compared with the results predicted by the previous mathematical models. The final design of the new paddle wheel valve with the 3-key component antisiphoning system was tested in the hydrodynamics laboratory to prove that the siphoning effect did not occur. According to the calculations obtained using the LabVIEW program during the experiments, each time the distal pressure decreased without an increase in the proximal pressure (despite the range of the pressure gradient), the pin blocked the spinning of the paddle wheels, and the calculated fluid velocity through the system tended to zero. Such a situation was significantly different from the expected flow rate for such a pressure gradient in a siphoning situation without the new antisiphon system. The design of this new prototype with a 3-key component antisiphoning system demonstrated that it is possible to decouple the activation pressure and the pressure gradient across the valve, avoiding the siphoning effect. Although further developments are necessary to provide a model compatible to clinical use, the authors believe that this new prototype illustrates the possibility of successfully addressing the siphoning effect by using a simple 3-key component system that is able to decouple the activation pressure and the pressure gradient across the valve by using a separate pressure chamber. It is expected that such proof of concept may significantly contribute to future shunt designs attempting to address the problem of overdrainage due to the siphoning effect.

Acquired isolated unilateral fourth nerve palsy after ventriculoperitoneal shunt surgery

Ventriculoperitoneal shunt has been the surgical procedure of choice for many years for both communicating and noncommunicating hydrocephalus.(1) High failure rates and complications have been reported, despite major improvements in shunt technology(2); however, fourth (trochlear) nerve palsy has not been reported after this procedure. We describe 2 patients who developed a fourth nerve palsy after shunt surgery. Recovery was incomplete, and strabismus surgery was required.

Complications of Lumboperitoneal Shunts

In Reply: As Dr. Lehman points out, in his letter in response to our article (1), LP shunts have been in existence for over 50 years. Throughout the years, advancements in surgical technique and shunt parts have improved LP shunt efficacy while reducing the complication rate. As Dr. Lehman notes, the introduction of the horizontal-vertical valve is a relatively recent advance in LP shunt technology. We believe that the horizontal-vertical valve has overcome many of the shortcomings of LP shunts from the past, such as overdrainage and the inability to access the shunt for testing. As experience is gained from the newer LP shunt technology, it is likely that LP shunts will prove their utility in selected groups of patients for cerebrospinal fluid diversion. Vincent Y. Wang Michael McDermott San Francisco, California

Preliminary study of shunt related death in paediatric patients

Hydrocephalus is a condition commonly encountered in paediatric and adult neurosurgery and cerebrospinal fluid (CSF) shunting remains the treatment of choice for many cases. Despite improvements in shunt technology and technique, morbidity and mortality remain. The incidence of early shunt obstruction is high with later failures seen less frequently. This review aims to examine mortality associated with mechanical failure of CSF shunts within Queensland. Neurosurgical and Intensive Care databases were reviewed for cases of mortality associated with shunt failure. Eight cases were identified between the years of 1992 and 2002 with the average age at death 7.7 years. Deaths occurred on average 2 years after last shunt revision. Seven of the eight patients lived outside the metropolitan area. Shunting remains an imperfect means of treating hydrocephalus. Mortality may be encountered at any time post surgery and delays to surgical intervention influence this. Alternative measures such as third ventriculostomy or the placement of a separate access device should be considered. In the event of emergency, a spinal needle could be used to access the ventricle along the course of the ventricular catheter.

Cerebrospinal Fluid Shunt Survival and Etiology of Failures: A Seven-Year Institutional Experience

Background: Innovations in shunt technology and neuroendoscopy have been increasingly applied to shunt management. However, the relative life span of shunts and the etiology of shunt failure have not been characterized recently. Methods: We reviewed the records of all shunting procedures at our institution between January 1992 and December 1998. Independent predictors of shunt failure were analyzed via multivariate Cox regression analysis in 836 shunting procedures. Independent predictors of the etiology of failure (infection, proximal obstruction, distal malfunction) were analyzed via multivariate logistic regression analysis in the 383 shunts which failed. Results: A total of 353 pediatric patients underwent 308 shunt placements and 528 revisions. The risk (hazard ratio; HR) of shunt failure decreased as a function of time in both primary placements and revised shunts. In failed shunts, the odds of infection decreased 4-fold per year of shunt function, while the odds of distal malfunction increased 1.45-fold per year. Increasing number of shunt revisions (HR 1.31, p < 0.05), decreasing patient age in years (HR 1.04, p < 0.001), gestational age <40 weeks (HR 2.15, p < 0.001) but not the etiology of hydrocephalus were associated with an increased risk of shunt failure. Revisions versus primary placements, Dandy-Walker cysts and gestational age <40 weeks were independently associated with proximal, distal and infectious causes of failure, respectively. Conclusions: The long-term shunt revision rates observed here are similar to those reported over the past 2 decades. Shunt life span remains poorer in shunt revisions and in younger patients. Patient characteristics may suggest a specific risk and mechanism of failure, aiding in the long-term management of shunted hydrocephalus.

O-29-425 - Shunt technology. What is the state-of-the-art?

O-29-425 - Shunt technology. What is the state-of-the-art?

The CSF accumulator: its role in the central nervous system and implications for advancing hydrocephalus shunt technology.

The 'cerebrospinal fluid (CSF) accumulator' plays an important physiological role in the healthy central nervous system as both a shock absorber and regulator of drainage. In the presence of hydrocephalus, this function is compromised by resistance to the flow of CSF. It is further compromised by the placement of a standard shunt which allows only for one-way directional diversion of the fluid. Complications associated with shunt dependency may be a direct consequence of both the condition, and a failure of existing systems to restore the normal accumulator function. This article reviews the pathophysiology of the 'CSF accumulator' as it relates to hydrocephalus and its management, and proposes a biomimetic shunt designed to restore the 'CSF accumulator' toward normal. It is hoped that such a device will support normalization of intracranial pressure and restore an appropriate level of CSF volume in the shunted patient.

Portal hypertension in children.

Portal hypertension is an uncommon but serious complication in children. The etiology may be intrahepatic or from an extrahepatic vascular occlusion. The pathophysiology is unknown, but the development of increased vascular resistance and portal flow are believed to be the primary changes. Increased portal flow is created by a decrease in systemic vascular resistance regionalized to the splanchnic vascular bed. Abnormally reduced response to vasoactive substances may be responsible. Advances in ultrasonography and endoscopy may improve our ability to evaluate portal hypertensive vascular changes. However, pharmacologic management is still limited to controlling the hemodynamic disturbances after they have occurred. Nonsurgical shunt management is increasingly being used in children, limiting the need for surgical shunt placement. Liver transplantation is now a viable option for managing end-stage disease. Future management depends on understanding the role of vasoactive substances controlling portal flow velocity, subsequent development of targeted pharmacologic therapy, and application of nonsurgical shunt technology in children. Transjugular intrahepatic portosystemic shunt placement is the next technologic advance moving from the adult into the pediatric realm.

Overdrainage and shunt technology

When vertical body position is simulated, conventional differential pressure valves show an absolutely unphysiological flow, which is 2-170 times the normal liquor production rate. Although this is compensated in part by the resistance of the silicon tubes, which may produce up to 94% of the resistance of the complete shunt system, a negative intracranial pressure (ICP) of up to 30-44 cmH2O is an unavoidable consequence, which can be followed by subdural hematomas, slit ventricles, and other well-known complications. Modern shunt technology offers programmable, hydrostatic, and "flow-controlled" valves and anti-siphon devices; we have tested 13 different designs from 7 manufacturers (56 specimens), using the "Heidelberg Valve Test Inventory" with 16 subtests. "Programmable" valves reduce, but cannot exclude, unphysiological flow rates: even in the highest position and in combination with a standard catheter typical programmable Medos-Hakim valves allow a flow of 93-232 ml/h, Sophy SU-8-valves 86-168 ml/h with 30 cmH2O. The effect of hydrostatic valves (Hakim-Lumbar, Chhabra) can be inactivated by movements of daily life. The weight of the metal balls in most valves was too low for adequate flow reduction. Antisiphon devices are highly dependent on external, i.e. subcutaneous, pressure which has unpredictable influences on shunt function, and clinically is sometimes followed by shunt insufficiency. Two new Orbis-Sigma valves showed relatively physiological flow rates even when the vertical position (30 cmH2O) was simulated. One showed an insufficient flow (5.7 ml/h), and one was primarily obstructed. These have by far the smallest outlet of all valves. Additionally, the ruby pin tends to stick. Therefore, a high susceptibility to obliterations and blockade is unavoidable. Encouraging results obtained in pediatric patients contrast with disappointing experiences in some German and Swedish hospitals, which suggests that our laboratory findings are confirmed by clinical results. The concept of strict flow limitation seems to be inadaequate for adult patients, who need a relatively high flow during (nocturnal) ICP crises. The problem of shunt overdrainage remains unsolved.