Considerations in the Use of Gravitational Valves in the Management of Hydrocephalus. Some Lessons Learned with the Dual-Switch Valve

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. These valves fail to maintain IVP within physiological limits due to the changes in hydrostatic pressure in the drainage system. To solve this problem more complex third-generation hydrostatic valves have been designed. These gravitational devices aim to reduce flow through a shunt system when the patient is upright but there are important technical differences between them. Here we review the main characteristics of the Miethke^® Dual-Switch valve, 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 paper specifies the main advantages and drawbacks of this device and 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 some the caveats neurosurgeons should take into consideration when using gravitational devices in 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 more than 45° might eliminate the beneficial effect of these devices.

Keywords: Dual-Switch valve; complications; gravitational valves; hydrocephalus; hydrostatic valves; shunt dysfunction.

Figure 1

(A) Cross-section of the Miethke^® Dual-Switch valve (DSV). It has a solid titanium casing (1). Two titanium plates (3) are integrated into diaphragms made of silicone (2). Each plate, together with a ball (4), creates a valve seat, which is integrated into the casing as an opening and closing mechanism. Two different springs control the position of the plates. There is a stronger spring for the high-pressure chamber (5) and a weaker one for the low-pressure chamber (6). A heavy tantalum ball (7) is used to shift the flow path to either chamber. Titanium lips are used for the inlet (8) and outlet (9) tubing connection. When patients are supine (B), the low-pressure chamber operates like a conventional DPV and is activated when the differential pressure is above the opening pressure of the valve. In the upright position (C), the low-pressure valve is closed, and the postural changes move a tantalum ball that opens the flow path for the high-pressure controller [7].

Figure 2

Method of selecting a suitable pressure for the high-pressure valve in the Miethke^® Dual-Switch valve. (1) Measure the distance between the third ventricle (external auditory meatus) and the patient’s diaphragm (costal arch); (2) subtract 5 cm from the measured distance; (3) choose a valve whose high-pressure setting exceeds the final measured value by the smallest amount.

Figure 3

Intracranial pressure (ICP) readings from a patient with idiopathic intracranial hypertension before (A) and after the implantation of a 10/40-cm H2O Miethke^® Dual-Switch valve (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.

Figure 4

(A) A 10/50-cm H2O Miethke^® Dual-Switch valve (M-DSV) implanted in a 75-year-old woman affected by normal pressure hydrocephalus (NPH). Note how the vertical axis of the valve is perfectly aligned with the vertical axis of the patient’s spine. This is the recommended position when this type of valve is inserted. The device is anchored to the muscular plane by a 0-silk suture. (B,C) Chest X-ray of the thoracic implantation site of the M-DSV in several 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.

Figure 5

Images of Miethke^® Dual-Switch valves (M-DSV) explanted after diagnosing a fracture 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 sutured to the connector, indicating that a fracture of the catheter at the distal end of the connector had occurred and not a disconnection of the catheter due to failure of the suture.

Figure 6

Schematic diagrams and real images of the first (A), second (B), and third (C) generation of the Miethke^® Dual-Switch Valve. Among other aspects, the most important design improvement was the mechanical robustness of the catheter-connector linkage (arrows).