Journal of Clinical Medicine Review Considerations in the Use of Gravitational Valves in the Management of Hydrocephalus. Some Lessons Learned with the Dual-Switch Valve Maria A. Poca 1,2,3, * , Dario F. Gándara 1,2 , Katiuska Rosas 1,2 , Aloma Alcina 1 , Diego López-Bermeo 1 and Juan Sahuquillo 1,2,3 1 Department of Neurosurgery, Vall d’Hebron Hospital Universitari, Vall d’Hebron Barcelona Hospital Campus, Passeig Vall d’Hebron 119-129, 08035 Barcelona, Spain; dfgandara@vhebron.net (D.F.G.); krosas@vhebron.net (K.R.); aalcina@vhebron.net (A.A.); y2961706x@vhebron.net (D.L.-B.); sahuquillo@neurotrauma.net (J.S.) 2 Neurotrauma and Neurosurgery Research Unit, Vall d’Hebron Institut de Recerca (VHIR), Vall d’Hebron Hospital Universitari, Vall d’Hebron Barcelona Hospital Campus, Passeig Vall d’Hebron 119-129, 08035 Barcelona, Spain 3 Department of Surgery, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain * Correspondence: pocama@neurotrauma.net; Tel.: +34-93-489-35-14; Fax: +34-93-489-41-88 Abstract: In the past decade, there has been a clear trend towards better outcomes in patients with hydrocephalus, especially those with normal pressure hydrocephalus (NPH). This is partly due to the availability of more sophisticated hardware and a better understanding of implants. However, there is little evidence to show the superiority of a specific type of valve over another. The most commonly reported consequence of hydrodynamic mismatch is shunt over-drainage.  Simple differential pressure valves, with a fixed opening pressure or even adjustable valves, lead to  non-physiologic intraventricular pressure (IVP) as soon as the patient moves into an upright posture. Citation: Poca, M.A.; Gándara, D.F.; These valves fail to maintain IVP within physiological limits due to the changes in hydrostatic Rosas, K.; Alcina, A.; López-Bermeo, pressure in the drainage system. To solve this problem more complex third-generation hydrostatic D.; Sahuquillo, J. Considerations in valves have been designed. These gravitational devices aim to reduce flow through a shunt system the Use of Gravitational Valves in the when the patient is upright but there are important technical differences between them. Here we Management of Hydrocephalus. review the main characteristics of the Miethke® Dual-Switch valve, which includes two valve Some Lessons Learned with the chambers arranged in parallel: a low-opening pressure valve, designed for working in the supine Dual-Switch Valve. J. Clin. Med. 2021, position, and a second high-opening pressure valve, which starts working when the patient assumes 10, 246. https://doi.org/10.3390/ the upright position. This paper specifies the main advantages and drawbacks of this device and jcm10020246 provide a series of recommendations for its use. The discussion of this specific gravitational valve allows us to emphasize the importance of using gravitational control in implanted shunts and Received: 13 December 2020 Accepted: 7 January 2021 some the caveats neurosurgeons should take into consideration when using gravitational devices in Published: 12 January 2021 patients with hydrocephalus. The correct function of any gravitational device depends on adequate device implantation along the vertical body axis. Misalignment from the vertical axis equal to or Publisher’s Note: MDPI stays neu- more than 45◦ might eliminate the beneficial effect of these devices. tral with regard to jurisdictional clai- ms in published maps and institutio- Keywords: complications; Dual-Switch valve; gravitational valves; hydrocephalus; hydrostatic nal affiliations. valves; shunt dysfunction Copyright: © 2021 by the authors. Li- 1. Introduction censee MDPI, Basel, Switzerland. This article is an open access article Hydrocephalus is a common disease treated in neurosurgical departments. Valve se- distributed under the terms and con- lection is an important factor for optimizing patient outcome. When differential-pressure ditions of the Creative Commons At- valves (DPV) were introduced in the late 1950s, the neurosurgeon could select between tribution (CC BY) license (https:// high, medium, or low opening pressure valves. However, it soon became evident that creativecommons.org/licenses/by/ over-drainage and its related complications (e.g., postural headaches, subdural bleeding, 4.0/). J. Clin. Med. 2021, 10, 246. https://doi.org/10.3390/jcm10020246 https://www.mdpi.com/journal/jcm J. Clin. Med. 2021, 10, 246 2 of 14 and subdural collections) were a direct consequence of the gravitationally-induced over- drainage when patients assume a standing or sitting position. The transition from the first generation of DPV to the more complex designs introduced later was a consequence of both neurosurgeons’ and engineers’ attempts to control the siphon effect that the DPV causes when the patient stands. In the early 1970s, measurements of intracranial pressure (ICP) in patients revealed that pressure in the lateral ventricles was sub-atmospheric when the patient is erect [1]. The first DPV generation systematically induced a significant increase in the magnitude of negative ICP when patients were sitting or standing [1,2]. The negative shunt-induced ICP was attributed to the gravity-induced ‘siphoning’ effects, an intrinsic flaw of DPVs that were designed to work on the differential pressure between the ICP and the pressure where the distal catheter was placed, usually in the right atrium or in the peritoneum. Siphoning induces shunt over-drainage and is the cause of many reported adverse effects after shunting [3]. In recent decades, a wide variety of valves, shunt designs, and devices for siphon- control or gravity-compensating devices have been introduced [4]. Today, we must choose among valves with different opening pressures, variable hydrodynamics, and adjustable (‘programmable’) valves with or without incorporated ‘antisiphon’ or gravitational devices. The use of gravitational devices incorporated into the valve or added in series into the distal catheter can produce a more physiological cerebrospinal fluid (CSF) drainage through the shunt, reducing the complications of over-drainage. A pragmatic randomized controlled study in patients with idiopathic NPH (iNPH) showed that the use of a gravitational valve prevented one over-drainage complication in every third patient undergoing shunting compared with a non-gravitational programmable valve [5]. One of the first gravitational valves designed was the Miethke® Dual-Switch valve (M- DSV; Aesculap, AG, Tuttlingen, Germany), which includes two valve chambers arranged in parallel: a low-opening pressure valve, designed for working in the supine position, and a second high-opening pressure valve, which starts working when the patient assumes the upright position. This device has been used for decades, especially in Europe and Japan [5]. The M-DSV has also been the main device used at our center since the second half of the 1990s. Subsequently, other smaller gravitational valves have displaced the use of the M-DSV in most centers. The M-DSV is still available, is a good example of the gravitational device, and presents some differential characteristics that must be considered when selecting a valve for a spe- cific patient. Here, we describe the characteristics of the M-DSV, its main advantages and drawbacks, and use our center learning curve with gravitational devices to make some recommendations for their use. The discussion of this gravitational valve allows us to emphasize the importance of using gravitational control in patients with hydro- cephalus in which a shunt is implanted. We also want to discuss some of the issues that neurosurgeons should take into consideration when using gravitational devices in patients with hydrocephalus. 2. The Miethke® Dual-Switch Valve The M-DSV is a robust device with a titanium casing designed by biomedical engi- neers at the Technical University of Berlin in close cooperation with the neurosurgical department of the Virchow Klinikum, Free University Berlin (nowadays Charité, Hum- boldt University, Berlin, Germany) and the neurosurgical department of the University Hospital Essen. It is designed for subcutaneous implantation in the thoracic region of adult patients [6,7]. The device has a diameter of approximately 28 mm and is 6 mm thick, a thickness that is comparable to other valves and is distinctly thinner than a pacemaker, another device typically implanted subcutaneously in the thoracic region. Because of its design, subcutaneous pressure does not influence the M-DSV performance, as has been shown with other over-drainage-compensating devices, such as antisiphon valves [8]. M-DSV safety is also increased because it is better than other conventional valves for the J. Clin. Med. 2021, 10, x FOR PEER REVIEW 3 of 14 J. Clin. Med. 2021, 10, 246 3 of 14 valves [8]. M-DSV safety is also increased because it is better than other conventional valves for the drainage of viscous CSF, which might include proteins and cell debris [6,7]. This is because in the M-DSV, the area exposed to the fluid pressure is about 200-times drainage larger thanof viscous in otherCSF, which valves mightsystematically which include proteins andtocell leads debrisacting higher [6,7]. This is because (spring) forces in the M-DSV, the area exposed to the fluid pressure is about 200-times larger than in other which are consequently less affected by changed viscosity or debris [6]. The M-DSV in- valves which systematically leads to higher acting (spring) forces which are consequently cludes two valve chambers arranged in parallel. The first, low-opening pressure valve is less affected by changed viscosity or debris [6]. The M-DSV includes two valve chambers designed for working in the supine position, and the second, high-opening pressure arranged in parallel. The first, low-opening pressure valve is designed for working in valve starts working when the patient assumes the upright position. The pressure of both the supine position, and the second, high-opening pressure valve starts working when of these elements is controlled by ball-in-cone valves, and their main objective is to the patient assumes the upright position. The pressure of both of these elements is con- maintain ICP values within physiological ranges regardless of the patient’s posture trolled by ball-in-cone valves, and their main objective is to maintain ICP values within (Figure 1) [7]. When patients are supine, the low-pressure chamber operates like a con- physiological ranges regardless of the patient’s posture (Figure 1) [7]. When patients are ventional DVP and is activated when the differential pressure is above the opening supine, the low-pressure chamber operates like a conventional DVP and is activated when pressure (OP) of the valve. In the upright position, the low-pressure valve is closed by a the differential pressure is above the opening pressure (OP) of the valve. In the upright tantalum ball. Afterward the control of the ventricular pressure in the upright position of position, the low-pressure valve is closed by a tantalum ball. Afterward the control of the the patient pressure ventricular is shifted in to thethe high-pressure-chamber upright position of the patient of the M-DSV, is shifted andhigh-pressure- to the the postural changes move chamber of theaM-DSV, tantalum and ball the[7] that opens postural the flow changes movepath for the high-pressure a tantalum control- ball [7] that opens the flow path for the high-pressure controller (Figure 1). The OP of this second valve is the ler (Figure 1). The OP of this second valve is higher and takes into consideration ad- higher ditional hydrostatic pressure of at least +35 cm H 2O, which occurs in the upright position. and takes into consideration the additional hydrostatic pressure of at least +35 cm H2 O, The opening which occurs pressure for theposition. in the upright upright Theposition mustpressure opening be selected according for the uprighttoposition the height mustof the patient. At present, the M-DSV is available with an OP of 5–16 cm H be selected according to the height of the patient. At present, the M-DSV is available with2O for the supine position an OP of and 5–1630–50 cm HcmH 2O for the upright position. For lumboperitoneal (LP) shunts, the 2 O for the supine position and 30–50 cmH2 O for the upright position. available For pressure settings lumboperitoneal for the lower-pressure (LP) shunts, valve issettings the available pressure 10 cm Hfor2O the andlower-pressure for the upright position it is 30–50 cmH O. Table 1 summarizes the pressures provided valve is 10 cm H2 O and for the upright position it is 30–50 cmH2 O. Table 1 summarizes 2 by the manu-the facturer. pressures provided by the manufacturer. Figure 1.1. (A) Figure (A)Cross-section Cross-sectionofofthe the Miethke Miethke ® Dual-Switch valve (DSV). It has a solid titanium casing (1). Two titanium ® Dual-Switch valve (DSV). It has a solid titanium casing (1). Two titanium plates plates (3) are integrated into diaphragms made of silicone (2). Each plate, together with a ball (4), creates a valve seat, (3) are integrated into diaphragms made of silicone (2). Each plate, together with a ball (4), creates a valve seat, which is which is integrated into the casing as an opening and closing mechanism. Two different springs control the position of integrated into the casing as an opening and closing mechanism. Two different springs control the position of the plates. the plates. There is a stronger spring for the high-pressure chamber (5) and a weaker one for the low-pressure chamber There (6). A is a stronger heavy tantalum spring ballfor (7)the high-pressure is used to shift thechamber (5) to flow path and a weaker either one for chamber. the low-pressure Titanium lips are used chamber for the (6). inletA(8) heavy and tantalum outlet (9)ball (7) isconnection. tubing used to shift the flow When path are patients to either supinechamber. (B), theTitanium lips are low-pressure used foroperates chamber the inletlike (8) and outlet (9) tubing a conventional DPV connection. When and is activated whenpatients are supinepressure the differential (B), the low-pressure chamber is above the opening operates pressure oflike the avalve. conventional DPV and In the upright is activated position (C), the low-pressure when valve pressure the differential is closed, and the is above postural pressure the opening changesofmove a tantalum the valve. ball that In the upright opens position (C),the the flow path for low-pressure the valve high-pressure is closed, and thecontroller postural[7]. changes move a tantalum ball that opens the flow path for the high-pressure controller [7]. J. Clin. Med. 2021, 10, 246 4 of 14 Table 1. Closing pressures stated by the manufacturers (left) compared to the pressure values found in the tested shunts by Czosnyka at the UK Shunt Evaluation Laboratory (right, in parenthesis) for different models of Dual-Switch valves. Pressure Settings for Ventriculoperitoneal Shunts Low Pressure High Pressure Low Pressure High Pressure (Supine Position) (Upright Position) (Supine Position) (Upright Position) mm H2 O mm H2 O mm Hg mm Hg 5* 30 3.7 22.0 5* 40 3.7 29.4 5* 50 3.7 36.8 10 30 7.4/(7 ± 0.6) ** 22.0/(22 ± 2.1) ** 13 30 9.5/(9.5 ± 0.4) ** 22.0 16 30 11.8/(12 ± 1.1) ** 22.0 10 40 7.4 29.4/(28 ± 1.9) ** 13 40 9.5 29.4 16 40 11.8 29.4 10 50 7.4 36.8/(38 ± 2.2) ** 13 50 9.5 36.8 16 50 11.8 36.8 Pressure Settings for Lumboperitoneal Shunts 10 30 7.4 22.0 10 40 7.4 29.4 10 50 7.4 36.8 * Valves especially designed for patients with normal pressure hydrocephalus. Adapted from the UK Shunt Evaluation Laboratory Report [9]. ** Pressure values found in the tested shunts by Czosnyka et al. [10] Values here are given as mean ± standard deviation. 3. Dual-Switch Valve Performance Reported by the Manufacturer In in vitro tests carried out by the manufacturers, the M-DSV has shown good and pre- dictable performance [6,7]. In terms of sensitivity to changes in CSF viscosity, composition, and sticking, as well as the influence of the pressure of the subcutaneous tissues, the M-DSV has superior performance compared with other valves [6,7]. Stepwise changes conducted in the laboratory–simulating changes from the upright to the supine position–demonstrated that ICP remains consistently within physiological limits [6]. The authors emphasize that all in vitro testing carried out provided strong evidence for the capability of the M-DSV to maintain intraventricular pressure within physiological ranges, regardless of changes in CSF flow and posture. The investigations substantiate the theoretical concept that the M-DSV is less affected by atypical CSF compositions in contrast to all other clinically used valves for treatment of hydrocephalus. 4. Independent Evaluation of the Performance of the Dual-Switch Valve The UK Shunt Evaluation Laboratory assess the hydrodynamic properties of all types of shunts available in the UK [11,12]. This group has evaluated many valves available in the market, offering important and independent information that every neurosurgeon should consider when selecting a valve for a specific patient. The main aims of these authors have always been to: (1) assess hydrodynamic properties of a shunt regardless of the manufacturer; (2) check whether the shunt performs according to the manufac- turer’s specifications and whether it complies with international standards (ISO/DIS7197); (3) characterize drainage capabilities with a more extensive range of tests than those listed in the ISO standard, and (4) summarize what is known from the literature about a shunt’s performance [9]. In these studies, the long-term stability of valve performance is tested in a laboratory environment that simulates the conditions within the human body, with the aim of demonstrating whether the shunt is susceptible to alterations in CSF drainage caused by postural changes, external pressure, change in ambient temperature, and/or the presence of a pulsating pattern in the inlet pressure, among other aspects [9]. J. Clin. Med. 2021, 10, 246 5 of 14 In the report evaluation of the M-DSV, 11 valves were tested [9]. The authors demon- strated that M-DSV valves could limit drainage in a stepwise manner when the gravitational valve axis changed from horizontal to vertical. The performance was stable and durable, regardless of ambient pressure, temperature, or magnetic field. None of the parameters (OP, closing pressure (CP), and resistance of the shunt ()) were altered by changes in temperature (30–40 ◦ C). Both OP and CP displayed minor variations (less than 1.5 mm Hg) in all tests. Good agreement of the operating pressures with the manufacturer’s data was recorded (differences of less than 1 mm Hg), and differences in measured parameters were minor among all tested valves. The valves did not show reflux when tested according to the ISO standard and did not exhibit a reversal of flow for an outlet-inlet differential pressure of up to 100 mm Hg [9,10]. Table 2 summarizes the technical findings reported by this group. Table 2. Evaluation of the performance and hydrodynamic properties of Miethke® Dual-Switch valves (M-DSV) by the U.K. Shunt Evaluation Laboratory. All the shunts showed mechanical durability over the period of testing (>48 days) Mechanical Durability and good stability of hydrodynamic performance over a 28-day period. Very well defined and stable in time, linearly changing with performance level. The Opening and Closing Pressures distal catheter did not change the opening and closing pressure significantly. The PFPC, operating, opening, and closing pressures were stable, with minimal Pressure-Flow Performance Curves scatter, and were in accordance with data reported by the manufacturer for valves (PFPC) working in both horizontal and vertical positions. There was no hysteresis of PFPC. Slight hysteresis (but very narrow, 1 mm Hg of Hysteresis of the PFPC width) appeared after connection of the distal catheter. Pressure Changes Related to Body The valves showed increased stepwise operational pressure in vertical position Posture when compared to horizontal position, according to its fixed parameters. The valves have rather low and stable hydrodynamic resistance (2.2 ± 0.8 mm Hg/mL/min) and therefore are able to stabilize ICP according to the fixed settings. Hydrodynamic Resistance The addition of a distal catheter increases the shunt resistance to 2.9 ± 1.1 mm Hg/mL/min. Small particles (10 microns diameter) temporarily increased the valve’s hydrodynamic resistance to 7 mm Hg/mL/min. Large microspheres (with a diameter greater than erythrocytes—25 µm) were found to open the shunt Effect of Particles in Reagent temporarily (closing pressure decreased from around 9 to 3 mm Hg). In both cases, these effects were only temporary when the particles were washed out spontaneously and on the next day the valve returned to normal performance. The M-DSV complied with this international standard for the testing of ISO/DIS 7197 Compliances hydrocephalus valves. Preassembled junctions did not break when a test specimen was subjected to a load Resistance to Breakage and Leakage of of 1 Kg of force for 1 min. All junctions remained free from leakage when the water Preassembled Junctions pressure was increased to 3 kPa (about 25 mm Hg). The valves did not show any reflux when tested according to the ISO standard. Reflux Valves did not exhibit flow reversal for an outlet-inlet differential pressure of up to 100 mm Hg. Magnetic Influence Magnetic field 3T did not have any influence on the shunt’s performance. No change in operating pressure occurred when an environmental pressure of External Pressure Influence 7 mm Hg was applied. None of the parameters (opening, closing pressure, and resistance) were altered by a Temperature Influence temperature change of 30 ◦ C to 40 ◦ C. Adapted from the UK Shunt Evaluation Laboratory Report [9,10]. J. Clin. Med. 2021, 10, 246 6 of 14 5. The Effect of MRI on the Function of M-DSV The MR-compatibility of CSF shunts has become increasingly important with the growing number of high-field MR scanners employed and the new, powerful magnetic fields that will be available soon. Lindner et al. [13] evaluated three M-DSV valves before and after exposure to 3T MRI. The M-DSV does not have ferromagnetic properties because it is made of titanium, tantalum, and silicone [6,9]. In vivo, the valve is positioned in the thoracic region. All MRI experiments were performed on a 3T human-scale whole-body scanner (MAGNETOM Trio, Siemens, Erlangen, Germany) using a protocol analogous to clinical practice and with the valves mounted either on the side of a phantom aligned parallel to the axis of the main magnetic field or mounted perpendicularly [13]. Due to the chemical constituents of the valves, displacement or extensive heating of the devices was not expected, and the authors centered their evaluations on the functioning of the valves J. Clin. Med. 2021, 10, x FOR PEER REVIEW 6 of 14 as the crucial parameter. The authors found that 3T magnetic fields did not influence the stability and safety of the M-DSV, with clear evidence that the valves continued to function correctly [13]. after Due to the MR constituents chemical scanning of [13]. the valves, displacement or extensive heating of the devices was not expected, and the authors centered their evaluations on the func- 6. Pressure tioning Selection of the valves of the as the crucial Two Valves parameter. in the The authors foundM-DSV that 3T magnetic fields did not influence the stability and safety of the M-DSV, with clear evidence that the The M-DSV valves continued is available to function with correctly after MRseveral scanningOPs [13]. for the supine position and for the upright position as listed in Table 1. The most reliable procedure for selecting a valve OP is based 6. Pressure Selection of the Two Valves in the M-DSV on the results of continuous ICP monitoring before surgery. In practice, however, when ICP The M-DSV is available with several OPs for the supine position and for the upright recording is unavailable, most clinicians rely on the manufacturer’s recommendations [14]. position as listed in Table 1. The most reliable procedure for selecting a valve OP is based According on the results oftocontinuous the manufacturer, ICP monitoring the recommended before standard surgery. In practice, pressure however, when setting for the lower- pressure ICP recordingvalve (DualSwitch is unavailable, valve® most clinicians , Instructions rely for use. on the manufacturer’s C. Miethke GmbH & Co. KG, recommenda- tions [14]. According to the manufacturer, the recommended standard pressure setting Potsdam, Germany) is 10 cm H2O (5 cm H2 O for patients with NPH). The high-pressure for the lower-pressure valve (DualSwitch valve®, Instructions for use. C. Miethke GmbH &side of the Co. KG, valveGermany) Potsdam, is calculated is 10 cmas H2O a function (5 cm H2of thepatients O for patient’swithheight NPH). Theand is chosen so that with the patientside high-pressure upright, a ventricular of the valve is calculatedpressure of at as a function of least −5 cm the patient’s H2 Oand height is ismaintained (DualSwitch chosen valveso ® ,that with the patient Instructions upright,Adequate for use). a ventricular pressure of pressure isatcalculated least −5 cm H as2Ofollows: is (1) measurement maintained (DualSwitch valve®, Instructions for use). Adequate pressure is calculated as of the distance between the third ventricle (at the level of the follows: (1) measurement of the distance between the third ventricle (at the level of the foramen of Monro, roughly measured foramen fromroughly of Monro, the external measured auditory meatus) from the external and the auditory diaphragm meatus) (roughly measured at the and the dia- phragm level of (roughly measured the costal at the arch); (2)level of the costal subtract 5 cmarch); from(2)the subtract 5 cm from measured the distance; (3) choose a valve measured distance; (3) choose a valve with a high-pressure setting that exceeds the final with a high-pressure setting that exceeds the final measured measured value by the smallest amount (Figure 2). When these criteria are met, patient value by the smallest amount (Figure ICP would2). be When expectedthese criteria are to be maintained met, patient between −5 and +5ICPcmHwould 2O even beafterexpected the to be maintained betweenof− placement 5 shunt the and [14]. +5 cmH2 O even after the placement of the shunt [14]. Figure Figure 2. Method 2. Method of selecting of selecting a suitable a suitable pressure pressure for the for valve high-pressure the high-pressure valve in the Miethke® Dual- in the Miethke® Du- al-Switch Switchvalve. valve.(1) (1) Measure the distance Measure between the the distance third ventricle between (external the third auditory (external ventricle meatus) auditory meatus) and the and the patient’s diaphragm (costal arch); (2) subtract 5 cm from the measured distance; (3) choose patient’s diaphragm (costal arch); (2) subtract 5 cm from the measured a valve whose high-pressure setting exceeds the final measured value by the smallest amount. distance; (3) choose a valve whose high-pressure setting exceeds the final measured value by the smallest amount. J. Clin. Med. 2021, 10, 246 7 of 14 Hertel et al. used a different strategy in which the opening pressure for the upright position (UPP) was dependent upon the patient’s height (180 cm or less, UPP = 30 cm or 40 cm H2 O; height over 180 cm, UPP = 50 cm H2 O) [15]. However, these authors did not J. Clin. Med. 2021, 10, x FOR PEER REVIEW 7 of 14 consider the weight of the patient, which also determines the expected intra-abdominal pressure [16] and may explain the functional underdrainage found by some authors when using hydrostatic Hertel valves et [17,18]. al. used a different strategy in which the opening pressure for the upright position (UPP) was dependent upon the patient’s height (180 cm or less, UPP = 30 cm or 7. Intracranial40Pressure Changes cm H2O; height after over 180 M-DSV cm, UPP = 50 cmImplantation H2O) [15]. However, these authors did not consider the weight of the patient, which also determines the expected intra-abdominal The M-DSV was [16] pressure designed and mayto adjust explain theICP according functional to the supine underdrainage found byor upright some authorsposition of the patient,when avoiding over-drainage. using hydrostatic However, switching between pressure settings valves [17,18]. is not gradual but instead occurs at an angle of approximately 60–70◦ [6]. Consequently, 7. Intracranial Pressure Changes after M-DSV Implantation when changing patient position from horizontal to vertical, there is a short period in The M-DSV was designed to adjust ICP according to the supine or upright position which ICP reaches a non-physiological of the patient, avoiding over-drainage. negative However,value switchingdue to a pressure between delayed switching settings is of the tantalum ball. Thus, not gradual butifinstead the patient occurs at changes an angle of slowly from60–70° approximately the supine to the upright [6]. Consequently, when changing position, a situation patient position of moderate from horizontal over-drainage to vertical, can occur [6]. there is a period In this short period the in tantalum which ICP reaches a non-physiological negative value due to a delayed switching of the ball only diminishes tantalum ball. Thus, if the patient changes slowly from the supine to the upright position, valve- the flow throughout the valve as the ball starts to close the seat. Although this phenomenon a situation of temporary of moderate over-drainage can occurover-drainage has [6]. In this period the no serious tantalum ball only clinical consequences,diminishes it explains the the flowheadaches throughout the valve that as thepatients some ball startsmight to closepresent the valve-seat. during Alt- the first hough this phenomenon of temporary over-drainage has no serious clinical conse- days after shunt implantation when they assume the sitting or standing position. quences, it explains the headaches that some patients might present during the first days To avoid headaches, during the implantation after shunt first two days when after valvethe they assume implantation theposition. sitting or standing patient’s bed should To avoid preferably be headaches, kept flat during and not partly the first raised. two days Figure after valve 3 illustrates implantation the posture-induced the patient’s bed should preferably be kept flat and not partly raised. Figure 3 illustrates the posture-induced ICP ICP changes in a patient with idiopathic intracranial hypertension before and after the changes in a patient with idiopathic intracranial hypertension before and after the im- implantation of a 10/40 plantation of cm H2cm a 10/40 OH M-DSV. 2O M-DSV. Figure 3. Intracranial pressure (ICP) readings from a patient with idiopathic intracranial hypertension Figure 3. Intracranial pressure (ICP) readings from a patient with idiopathic intracranial hypertension before (A) and af- ® Dual-Switch valve ter thebefore (A) and implantation of a after theH2O 10/40-cm implantation of a 10/40-cm Miethke® Dual-Switch valve (B). H2O In the Miethke (B). In the posture-induced ICP changes after shunting (B), the patient remained supine for 1 h and then sat up and remained sitting for 3 h. posture-induced ICP changes after shunting (B), the patient remained supine for 1 h and then sat up and remained sitting for 3Aspects 8. Surgical h. in the Implantation of the M-DSV Antisiphon devices (ASDs) control over-drainage by increasing the resistance of the 8. Surgical Aspects in the Gravitational shunt (Rshunt). Implantation of (GDs) devices the M-DSV control over-drainage by increasing the OP Antisiphonof the valve through devices (ASDs)the control movementover-drainage of inbuilt metallic balls when the patient by increasing themoves from of the resistance the recumbent position. Consequently, the correct function of any GD depends on an shunt (Rshunt).adequate Gravitational devices (GDs) control over-drainage by increasing the OP of device’s vertical implantation. Any degree of deviation from the vertical axis the valve through the movement equal to or more than 45°of inbuilt metallic might eliminate theballs when beneficial theofpatient effect moves the device. A ret-from the recumbent position. Consequently, the correct function of any GD depends on an adequate device’s vertical implantation. Any degree of deviation from the vertical axis equal to or more than 45◦ might eliminate the beneficial effect of the device. A retro-auricular implantation of other gravitational valves, such as GAV and PaediGAV (Aesculap, AG, Tuttlingen, Germany), is common in both adults and pediatric patients. However, a correct vertical alignment should always be ensured because the movement of the head with relation to the body axis might compromise the performance of the device. In adults, we prefer to implant GDs based on ball technology in the chest to avoid or minimize (Aesculap, AG, Tuttlingen, Germany), is common in both adults and pediatric patients. However, a correct vertical alignment should always be ensured because the movement of the head with relation to the body axis might compromise the performance of the de- vice. In adults, we prefer to implant GDs based on ball technology in the chest to avoid or minimize this problem (Figure 4A). Additionally, the M-DSV has been specifically de- J. Clin. Med. 2021, 10, 246 signed to be implanted in the thorax. When this valve is implanted, the angle between the 8 of 14 vertical axis of the valve should not deviate more than 15° from the gravitational axis to avoid interference with the mechanical design of the valve. Another recommended precaution when implanting an M-DSV in the thorax is that it should be placed on a flat surface. In male patients, the valve can be placed at the in- this problem (Figure fraclavicular 4A). Additionally, or sub-mammary thebecause level. However, M-DSV of has been females’ specifically variable designed breast size, it to be implanted intothe is better thorax. place the valveWhen this valve islevel, at the sub-mammary implanted, thegrid, on the costal angleandbetween at enough the vertical axis ofdistance the valve should so that the bra not does deviate more not coincide withthan 15◦ from the valve. Finally,the gravitational given the dimensions axis to avoid and weight interference of the with thevalve (28×6 mm,design mechanical 11.6 g), itofmust the be sutured in the muscular plane with valve. a non-absorbable suture to ensure that the device does not move (Figure 4A). Figure 4. (A) A 10/50-cm H2O Miethke® Dual-Switch valve (M-DSV) implanted in a 75-year-old woman affected by Figure 4. (A) A 10/50-cm H2O Miethke ® normal pressure hydrocephalus (NPH).Dual-Switch valveaxis Note how the vertical (M-DSV) implanted of the valve is perfectlyin a 75-year-old aligned woman with the vertical axis affected by of the patient’s normal pressure spine. This(NPH). hydrocephalus is the recommended Note howposition when this the vertical type axis ofofthe valve is inserted. valve The device is perfectly is anchored aligned withtothethe vertical axis muscular plane by a 0-silk suture. (B,C) Chest X-ray of the thoracic implantation site of the M-DSV in several patients of the patient’s spine. This is the recommended position when this type of valve is inserted. The device is anchored to showing fractures of the catheters (red arrows). (B) Fracture of the distal catheter of the valve in a patient aged 23 years the muscularwith plane by a 0-silkassociated hydrocephalus suture. with (B,C) Chest spina X-ray bifida with of the thoracic abdominal implantation migration of the cathetersite of the (green M-DSV arrow). in several A fracture of patients showing fractures of the catheters (red arrows). (B) Fracture of the distal catheter of the valve in a patient aged 23 years with hydrocephalus associated with spina bifida with abdominal migration of the catheter (green arrow). A fracture of the distal catheter was diagnosed six years after implantation of the valve. (C) Fracture of the proximal and distal catheters of the valve in a patient with hydrocephalus associated with a Chiari type 1 malformation (red arrows). (D) Early distal catheter fracture (red arrow) when using a lumbo-peritoneal M-DSV. Although it would be expected that this problem would happen a few years after the implantation of the valve, in our center, we observed this problem only ten months after valve implantation in a 12-year-old child. The valve was replaced, and the child presented this problem for the second time one year after this second implantation. Greater mobility in children, when compared to adults, reinforces the fact that this type of valve has been designed for adults and should not be implanted in children. Another recommended precaution when implanting an M-DSV in the thorax is that it should be placed on a flat surface. In male patients, the valve can be placed at the infraclavicular or sub-mammary level. However, because of females’ variable breast size, it is better to place the valve at the sub-mammary level, on the costal grid, and at enough distance so that the bra does not coincide with the valve. Finally, given the dimensions and weight of the valve (28×6 mm, 11.6 g), it must be sutured in the muscular plane with a non-absorbable suture to ensure that the device does not move (Figure 4A). J. Clin. Med. 2021, 10, 246 9 of 14 9. Clinical Experience with M-DSV Use The first clinical experience with this device was reported by Sprung et al. [7,19]. In 1997, who reported on implants conducted in 35 adults with hydrocephalus of different etiologies. In a randomized study, the first 21 patients were compared with 21 patients who received a conventional medium DPV, revealing that DPV patients had a signifi- cantly higher percentage of over-drainage-related complications, such as hygromas and hematomas [19]. Trost et al. (1998) [20] reported their experience of M-DSV implantation in 32 adult patients. The clinical results were excellent to good, except for three cases with previous severe post-traumatic or post-hemorrhagic brain damage. The authors remarked that despite achieving a satisfying clinical improvement in most cases, they saw only minimal to slight reduction in ventricular size. Additionally, apart from one case of non-symptomatic transient hygroma attributed to a suboptimal alignment of the valve with the gravitational axis, the authors observed no valve-related complications, such as over-drainage, underdrainage, or dysfunction. In two patients, however, three revisions were necessary due to disconnections of the peritoneal catheter [20]. Table 3 summarizes the abbreviations and complete names of the valves mentioned in this review. Table 3. Abbreviations and complete names of the valves mentioned in this review. Abbreviation Complete Name Distributed by: Cordis-Standard INTEGRA LIFESCIENCES CSV differential-pressure valve CORPORATION, Ratingen, Germany DPV Differential-pressure valve GAV MIETHKE® gravitational valve Aesculap, AG, Tuttlingen, Germany Pediatric MIETHKE® PaediGAV * Aesculap, AG, Tuttlingen, Germany gravitational valve M-DSV Miethke® Dual-Switch valve Aesculap, AG, Tuttlingen, Germany INTEGRA LIFESCIENCES OSV Orbis Sigma valve CORPORATION, Ratingen, Germany * The MIETHKE paediGAV® is the smallest gravitational valve for the treatment of pediatric hydrocephalus. Zeilinger et al. (2000) reported their clinical experience with the M-DSV in patients with NPH [21]. The authors treated 117 NPH patients, 47 with a Cordis-Standard DPV (CSV, Integra DP™ Valve System, INTEGRA LIFESCIENCES CORPORATION, Ratingen, Germany), 20 with a type 1 Orbis Sigma valve (OSV ITM Valve System, INTEGRA LIFE- SCIENCES CORPORATION, Ratingen, Germany), and 50 with an M-DSV. Ninety-five patients (39, 19, and 49, respectively) were reexamined after a mean time interval of seven months. No statistical differences in mechanical and infectious complications were found between the different models. However, the authors found significant differences in over- drainage complications and subdural hematomas, which occurred in 6% of the patients treated with the CSV, in 26% of those treated with an OSV, and 5% of those treated with an M-DSV. Three patients with an Orbis-Sigma valve developed subdural hematomas that required surgical evacuation. Two patients with an M-DSV also developed subdural hematomas; in one of these patients, the hematoma was resorbed without clinical symp- toms, while in the other, the shunt had to be removed [21]. The authors concluded that the high incidence of over-drainage complications and subdural hematomas in the OSV group might contraindicate the use of this valve and that the hydrostatic M-DSV might be the best valve for NPH patients [21]. Similar conclusions were presented by Meier et al. [22] and later in a prospective multicenter study using the M-DSV in 128 patients with NPH [18]. A Japanese study demonstrated further interesting results derived from the use of M-DSV [23]. The authors implanted 94 M-DSVs in adult patients with hydrocephalus (10 cm H2 O until April 2003 and 5 cm H2 O from May 2003 in the supine position and 30 or 40 cm H2 O in the upright position according to height) and carried out IVP monitoring via the shunt reservoir on all patients for one week after shunt placement. Regardless of the valve settings selected, IVP in the sitting position was slightly below zero in most J. Clin. Med. 2021, 10, 246 10 of 14 patients, but no negative pressures below −15 cm H2 O were observed in any of them [24]. Unfortunately, at least six patients who showed initial clinical improvement after shunting worsened due to underdrainage, despite a patent shunt. These patients had been implanted with a shunt set at an OP of 10 cm H2 O for the supine position. In our experience, the best supine shunt OP for NPH is 5 cm H2 O or even lower. On the other hand, chronic subdural hematoma occurred in three patients. The authors concluded that the M-DSV could maintain physiological IVP in patients with hydrocephalus, regardless of posture, and provide a generally satisfactory clinical outcome, but it could not prevent all over- drainage-related problems [24]. Finally, Hertel et al. reported on the widest clinical experience with the use of the M-DSV to date [15]. Between 1998 and 2005, these authors implanted an M-DSV in 169 adult patients (70 with NPH). They reported a rate of shunt response of 93.2%, an over- drainage rate of 3.2%, and no valve obstruction in the entire series, including patients with relatively high CSF protein content (mean protein content in CSF was 50.1mg (18–122 mg)). The overall shunt survival rates among these patients were 86%, 84%, and 82 % after 1, 2, and 6 years, respectively [15]. The overall complication rate for the study period was 21%, the most frequent complication being revision of the peritoneal catheter (8%), followed by infection (6%), over-drainage (3.5%), revision of the ventricular catheter (1%), and other complications (2.5%) [15]. In this study, it is important to note the high rate of problems with the distal catheter. In our department, between October 2011 and November 2017, 127 ventriculoperi- toneal M-DSV valves were implanted. Forty-two of them had an OP of 5/30 cm H2 O, and in 85, the OP was 5/40 cm H2 O. 10. The Problem of Catheter Dislocation/Fracture in the M-DSV A specific problem associated with the use of VP or LP M-DSV is the potential fracture and disconnection of the proximal and/or distal catheters in the valve (Figures 4 and 5). We have observed this problem in many units of this device after at least 10 months from implantation. Visual inspection of removed devices (Figure 5) showed that the catheters have an irregular fracture surface with well-defined edges and maintain the typical elasticity and rubbery feel of the original catheter. Frequently, when this problem occurs, it is necessary to replace the valve and the distal catheter. In our center, some of the explanted devices have been returned for a bench test of the valves’ performance (Figure 5). In all the explanted valves, the manufacturer reported that the bench test for all these valves was correct. It has been suggested that catheter fractures in the M-DSV might be due to immuno- logical reactions against the silicone of the subcutaneously-fixed catheter [25]. However, to my knowledge this phenomenon has not yet been described in other gravitational valves implanted in the skull, such as the GAV or PaediGAV shunt systems, despite that the same type of materials and connections as the M-DSV valves implanted in the chest are used. The most probable hypothesis to explain this phenomenon is the stress generated by the movement of two different materials with the high inertial loading of the M-DSV due to its unusual weight. The greater mobility of the valves placed in the thorax produces shearing forces in the small region of the catheter where it leaves the device. The literature on catheter problems in hydrocephalus valves focuses mainly on the degradation, calcification, and aging of the catheter material, which becomes brittle over time [26]. Catheter failure or dislocation accounts for approximately 3% of complications in the M-DSV and typically occur more than five years after implantation [25]. Mechanical stress on the catheter combined with material degradation eventually leads to catheter failure, often occurring at places in which the catheter is under great dynamic stress. Some of the valves implanted at our center, however, were explanted before 12 months after implantation (Figure 4), well below the typical degradation time for this type of silicone catheter, and the typical signs of silicone-degradation were observed in none of them. This, therefore, argues that are other mechanical factors that play a role in catheter’s J. Clin. Med. 2021, 10, 246 11 of 14 breakage. J. Clin. Med. 2021, 10, x FOR PEER REVIEW The size and weight of the M-DSV probably plays a role in the mechanical forces 11 of 14 that act at the points were the proximal and distal catheter are attached. Figure 5. Images of Miethke® Dual-Switch valves (M-DSV) explanted after diagnosing a fracture of Figure 5. Images of Miethke® Dual-Switch valves (M-DSV) explanted after diagnosing a fracture the distal catheter of the valve. Fractures typically occur at the connector tip level of first (A) or of the distal catheter of the valve. Fractures typically occur at the connector tip level of first (A) or second (B) generation M-DSV. Note that at the distal end of the valve, there is a catheter fragment second sutured(B) togeneration M-DSV. the connector, Note that indicating thatat the distalofend a fracture the of the valve, catheter there at the is aend distal catheter of the fragment connector sutured to the connector, indicating that a fracture of the catheter at the distal had occurred and not a disconnection of the catheter due to failure of the suture. end of the connector had occurred and not a disconnection of the catheter due to failure of the suture. It has been suggested that catheter fractures in the M-DSV might be due to immu- In ourreactions nological patients, against the characteristics the siliconeofofthe thebroken catheter tips suggest subcutaneously-fixed a mechanical catheter [25]. How- failure ever, to my knowledge this phenomenon has not yet been described in other surface of the catheter following contact with the connector. This type of fracture gravita- is typical of breakage due to pure mechanical stress (Figure 5) and might be amplified tional valves implanted in the skull, such as the GAV or PaediGAV shunt systems, de- by chemical or enzymatical degradation or calcification of the catheter. A degraded spite that the same type of materials and connections as the M-DSV valves implanted in catheter, however, would typically leave a brittle, crumbly surface, and an overall change the chest are used. The most probable hypothesis to explain this phenomenon is the stress of consistency when compared to the newly implanted material, characteristics that were generated by the movement of two different materials with the high inertial loading of not observed in any of the broken catheters. If one assumes the catheter material has not the M-DSV due to its unusual weight. The greater mobility of the valves placed in the been degraded at the time of explantation, the failures reported in our patients suggest thorax produces shearing forces in the small region of the catheter where it leaves the mechanical stress in the catheter generated by the interaction between it and the metallic device. connector. This conclusion, also proposed by Trost et al. [20], is supported by the fact that The literature on catheter problems in hydrocephalus valves focuses mainly on the the medical device manufacturer released a second and third generation of the device degradation, calcification, and aging of the catheter material, which becomes brittle over (Figure 6), improving, among other aspects, the design and mechanical robustness of time [26]. Catheter failure or dislocation accounts for approximately 3% of complications the catheter-connector linkage. Although the manufacturer reinforced the material of in the this M-DSV critical and typically region, occur the first and more than second five years generation after valves of these implantation remain[25]. Mechan- in use and ical stress must on the catheter be controlled combined periodically. with material degradation In lumbo-peritoneal eventually leads valves, the manufacturer to cath- has not yet eter failure, often implemented occurring at places this improvement. in which no Furthermore, thelong-term catheter isstudies under great dynamic stress. on third-generation Some have valves of thebeen valves implanted carried out. at our center, however, were explanted before 12 months after implantation (Figure 4), well below the typical degradation time for this type of sil- icone catheter, and the typical signs of silicone-degradation were observed in none of them. This, therefore, argues that are other mechanical factors that play a role in cathe- ter’s breakage. The size and weight of the M-DSV probably plays a role in the mechanical forces that act at the points were the proximal and distal catheter are attached. In our patients, the characteristics of the broken catheter tips suggest a mechanical failure of the catheter following contact with the connector. This type of fracture surface is typical of breakage due to pure mechanical stress (Figure 5) and might be amplified by chemical or enzymatical degradation or calcification of the catheter. A degraded catheter, however, would typically leave a brittle, crumbly surface, and an overall change of con- sistency when compared to the newly implanted material, characteristics that were not observed in any of the broken catheters. If one assumes the catheter material has not been degraded at the time of explantation, the failures reported in our patients suggest me- chanical stress in the catheter generated by the interaction between it and the metallic connector. This conclusion, also proposed by Trost et al. [20], is supported by the fact that J. Clin. Med. 2021, 10, x FOR PEER REVIEW 12 of 14 the medical device manufacturer released a second and third generation of the device (Figure 6), improving, among other aspects, the design and mechanical robustness of the catheter-connector linkage. Although the manufacturer reinforced the material of this J. Clin. Med. 2021, 10, 246 critical region, the first and second generation of these valves remain in use and must be 12 of 14 controlled periodically. In lumbo-peritoneal valves, the manufacturer has not yet im- plemented this improvement. Furthermore, no long-term studies on third-generation valves have been carried out. Figure 6. Schematic diagrams and real images of the first (A), second (B), and third (C) generation of the Miethke® Du- Figure al-Switch 6. Schematic Valve. diagrams Among other aspects, andimportant the most real images of the firstwas design improvement (A), thesecond generation of (B), mechanical and third robustness of the(C) catheter-connector linkage ® (arrows). the Miethke Dual-Switch Valve. Among other aspects, the most important design improvement was the mechanical robustness 11. Final of theand Considerations catheter-connector Recommendations linkage (arrows). According to Aschoff et al. [27], an ideal shunt system should be: (1) effective in all 11. Final Considerations body positionsand with Recommendations compensation of postural changes in hydrostatic pressures; (2) re- sistant to movements and vibrations of daily life; (3) insusceptible to external pressure, Accordingflexion, to Aschoff et al. and torsion; [27],to an (4) able ideal effect shunt sufficient system drainage of flowshould be:nocturnal); peaks (e.g., (1) effective in all body positions(5)with compensation insensitive of postural to increased content of protein and changes in hydrostatic cellular material; pressures; and (6) able to retain (2) re- the desired properties for a very long time. Added to these characteristics would be the sistant to movements and vibrations of daily life; (3) insusceptible to possibility of adjusting the opening pressure of the valve. Although this ideal shunt sys- external pressure, flexion, and torsion; (4)yet tem has not able beento effect the developed, sufficient M-DSV hasdrainage many of these ofqualities. flow peaks (e.g., nocturnal); The hydrodynamic (5) insensitive to increased content properties of the and of protein M-DSV promise material; cellular to prevent posture-related and (6) able to retain over-drainage. In comparison to ASD, gravitational valves have the important advantage the desired properties for a very long time. Added to these characteristics of being unaffected by external or subcutaneous pressure [9]. Research (both by the would be the possibility of adjusting manufacturertheandopening pressure independently) carried ofout the valve. with Although small (10 this ideal microns diameter) shunt system and big has not yet beenparticles (diameter greater than 25 µm) has shown that the M-DSV has a better tolerance developed, the M-DSV has many of these qualities. to proteins and small quantities of blood in the CSF when compared with other valves The hydrodynamic properties [9,10]. This makes the M-DSV ofideal the for M-DSV promise implantation to prevent in patients posture-related with high levels of pro- over- teins and cells into drainage. In comparison the ASD, CSF. However, if we have implanted gravitational valves M-DSV, have especially of the first advantage the important and second generation without reinforcement at the junction point between the valve and of being unaffected the distalby external catheter (Figureor6C),subcutaneous pressure the follow-up of patients should[9]. includeResearch X-rays for de-(both by the manufacturer and independently) tecting carried potential catheter fracture at thisout pointwith small (10 microns diameter) and big over time. To conclude, based on the information reported in the present paper, a series of particles (diameter greater than 25 µm) has shown that the M-DSV has a better tolerance to recommendations must be considered when selecting the M-DSV: proteins and small • quantities The M-DSV is sof blood hunt devicein thatthe CSFposture-related controls when compared with other valves [9,10]. over-drainage. This makes the •M-DSV ideal The M-DSV for implantation is designed for adults and in patients should with high not be implanted levelsasof in children, proteins and they always have greater body mobility than adults. cells in the CSF. However, if we have implanted M-DSV, especially of the first and second generation without reinforcement at the junction point between the valve and the distal catheter (Figure 6C), the follow-up of patients should include X-rays for detecting potential catheter fracture at this point over time. To conclude, based on the information reported in the present paper, a series of recommendations must be considered when selecting the M-DSV: • The M-DSV is s hunt device that controls posture-related over-drainage. • The M-DSV is designed for adults and should not be implanted in children, as they always have greater body mobility than adults. • When implanting the M-DSV valve, the flattest part of the chest should be selected, and the device correctly fixed to the muscular plane so that the vertical direction of the valve is in line with the vertical axis of the patient’s body. • In terms of sensitivity to changes in CSF viscosity, composition, and sticking, as well as the influence of the pressure of the subcutaneous tissues, the M-DSV has superior performance compared with other valves [6,7]. • Due to the risk of fracture in the catheters at the level of the proximal or distal connectors of the valve, it is advisable to include in the patient’s follow-up periodic radiological controls for ruling out this potential problem. Author Contributions: Conception and design, M.A.P.; acquisition of data, M.A.P., D.F.G., K.R., A.A. and D.L.-B.; analysis and interpretation of data, M.A.P. and J.S.; draft the article, M.A.P. and J.S.; critically revising the article, all authors; review submitted version of manuscript, all authors; J. Clin. Med. 2021, 10, 246 13 of 14 approve the definitive version of the manuscript on behalf of all authors, M.A.P.; study supervision, M.A.P. and J.S. All authors have read and agreed to the published version of the manuscript. Funding: This study was partially supported by grant FIS (Fondo de Investigación Sanitaria) PI18/00468, which were co-financed by the European Regional Development Fund (ERDF), awarded to Maria A. Poca. Acknowledgments: We gratefully acknowledge the nurses of the Neurosurgery Department, espe- cially Eva Corral and Teresa Molina, for their collaboration in the studies performed. 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