Programmable Shunt Assistant Tested in Cambridge Shunt Evaluation Laboratory

The applicability of fixed and adjustable gravitational shunt valves in two different clinical settings

BACKGROUND

Gravitational shunt valves and most recently the adjustable proSA® gravitational valve have been designed to counteract overdrainage and thereby improving clinical outcome. So far, the applicability in a broader mix of hydrocephalus patients is unrevealed. The aim of this study was to evaluate the utility of gravitational valves in two different clinical settings.

METHODS

This retrospective double-center cohort study was enabled by two different shunt management policies. At Rigshospitalet, patients with a complicated shunt history receiving a proGAV® and proSA® shunt system during surgical revision were included, and clinical outcome in the follow-up periods before and after was compared. At Aarhus University Hospital, a combination of a proGAV® and a fixed (SA®) or adjustable (proSA®) gravitational valve was used in all shunt procedures. Clinical outcome in a 2-year follow-up period was compared to a cohort receiving non-gravitational valves in the period before the transition to gravitational valves.

RESULTS

Twenty-two patients were included at Rigshospitalet. Mean follow-up time before and after proGAV® and proSA® implantation was 2.3 and 1.5 years, respectively. In each patient, roughly two surgical revisions (p 0.031) and two hospitalizations (p 0.009) were avoided each year after proGAV® and proSA® implantation. At Aarhus University Hospital, 90 patients with non-gravitational valves and 98 patients with gravitational valves were included. Changes in clinical outcome parameters and shunt survivals were either stable or statistically insignificant.

CONCLUSIONS

Gravitational valves are safe and useful in clinical practice and represent an equivalent alternative as a first-line shunt valve in a broad mix of patients, while proSA® valves should be considered for complex shunt patients.

In vitro performance of the fixed and adjustable gravity-assisted unit with and without motion-evidence of motion-induced flow

BACKGROUND

Anti-siphon devices and gravitational-assisted valves have been introduced to counteract the effects of overdrainage after implantation of a shunt system. The study examined the flow performance of two gravitational-assisted valves (shunt assistant - SA and programmable shunt assistant - proSA, Miethke & Co. KG, Potsdam, Germany) in an in vitro shunt laboratory with and without motion.

METHODS

An in vitro laboratory setup was used to model the cerebrospinal fluid (CSF) drainage conditions similar to a ventriculo-peritoneal shunt and to test the SA (resistance of +20 cmH2O in 90°) and proSA (adjustable resistance of 0 to +40 cmH2O in 90°). The differential pressure (DP) through the simulated shunt and tested valve was adjusted between 0 and 60 cmH2O by combinations of different inflow pressures (40, 30, 20, 10, and 0 cmH2O) and the hydrostatic negative outflow pressure (0, -20, and -40 cmH2O) in several differing device positions (0°, 30°, 60°, and 90°). In addition, the two devices were tested under vertical motion with movement frequencies of 2, 3, and 4 Hz.

RESULTS

Both gravity-assisted units effectively counteract the hydrostatic effect in relation to the chosen differential pressure. The setting the proSA resulted in flow reductions in the 90° position according to the chosen resistance of the device. Angulation-related flow changes were similar in the two devices in 30-90° position, however, in the 0-30° position, a higher flow is seen in the proSA. Repeated vertical movement significantly increased flow through both devices. While with the proSA a 2-Hz motion was not able to induce additional flow (0.006 ± 0.05 ml/min), 3- and 4-Hz motion significantly induced higher flow values (3 Hz: +0.56 ± 0.12 ml/min, 4 Hz: +0.54 ± 0.04 ml/min). The flow through the SA was not induced by vertical movements at a low DP of 10 cmH2O at all frequencies, but at DPs of 30 cmH2O and higher, all frequencies significantly induced higher flow values (2 Hz: +0.36 ± 0.14 ml/min, 3 Hz: +0.32 ± 0.08 ml/min, 4 Hz: +0.28 ± 0.09 ml/min).

CONCLUSIONS

In a static setup, both tested valves effectively counteracted the hydrostatic effect according to their adjusted or predefined resistance in vertical position. Motion-induced increased flow was demonstrated for both devices with different patterns of flow depending on applied DP and setting of the respective valve. The documented increased drainage should be considered when selecting appropriate valves and settings in very active patients.

Female gender predisposes for cerebrospinal fluid overdrainage in ventriculoperitoneal shunting

BACKGROUND

Gravitational valves (GVs) prevent overdrainage in ventriculoperitoneal shunting (VPS). However, there are no data available on the appropriate opening pressure in the shunt system when implementing a GV. We performed a retrospective analysis of hydrocephalic patients who were successfully treated with VPS which included one or more GV.

METHOD

In this retrospective study in adult VPS patients with GVs, we analysed all available data, including the most recent computed tomography (CT) scans, to determine the best adjustments for alleviating any symptoms of overdrainage and underdrainage. Vertical effective opening pressure (VEOP) of the entire shunt system, including the differential pressure valve, was determined.

RESULTS

One hundred and twenty-two patients were eligible for the study. Of these, female patients revealed a higher VEOP compared with males (mean, 35.6 cmH2O [SD ± 2.46] vs 28.9 cmH2O [SD ± 0.87], respectively, p = 0.0072, t-test). In patients older than 60 years, lower VEOPs, by a mean of 6.76 cmH2O ± 2.37 (p = 0.0051), were necessary. Mean VEOP was found to be high in idiopathic intracranial hypertension (IIH; 41.6 cmH2O) and malresorptive and congenital HC (35.9 and 36.3), but low in normal pressure HC (27.5, p = 0.0229; one-way ANOVA). In the total cohort, body mass index (BMI) and height did not correlate with VEOP. Twelve patients required a VEOP of more than 40 cmH2O, and in eight of these patients this was accomplished by using multiple GVs. All but one of these eight patients were of female gender, and none of the latter were treated for normal pressure hydrocephalus (NPH) (p = 0.0044 and p = 0.0032, Fisher's exact test).

CONCLUSIONS

In adult VPS patients, female gender increases the risk of overdrainage requiring higher VEOPs. Initial implantation of adjustable GV should be considered in female patients treated with VP shunts for pathology other than NPH.

Feasibility of telemetric ICP-guided valve adjustments for complex shunt therapy

OBJECT

The advances in shunt valve technology towards modern adjustable differential pressure (DP) valves and adjustable gravitational assisted valves result in an increasing complexity of therapeutical options. Modern telemetric intracranial pressure (ICP) sensors may be helpful in their application for diagnostic purposes in shunt therapy. We present our first experiences on telemetric ICP-guided valve adjustments in cases with the combination of an adjustable DP valve and adjustable gravitational unit.

METHODS

Four consecutive cases were evaluated in a retrospective review who had received a proGAV adjustable, gravitational assisted DP valve with secondary in-line implantation of an adjustable shunt assistant (proSA), together with a telemetric ICP sensor (Neurovent-P-tel) between December 2010 and June 2012 in our institution. The measured ICP values and the corresponding valve adjustments were analyzed in correlation with the clinical course and the cranial imaging of the patients.

RESULTS

No surgery-related complications were observed after implantation of the proSA and the telemetric ICP sensor additional to the proGAV. ICP values could actively be influenced by adjustments of the respective valve units. An increase of the position depending resistance of the proSA resulted in significant attenuated negative ICP values for the standing position, while adjustments of the proGAV could be detected not only in a supine position but also in a standing position. A clinical improvement could be achieved in all cases.

CONCLUSION

The combination of adjustability in the differential pressure valve and the gravitational unit reveals a complex combination which may be difficult to adapt only according to clinical information. Telemetric ICP-guided valve adjustments seem to be a promising tool as an objective measure according to different body positions. Further investigations are needed to select the patients for these costly implants.