Fixed-Pressure vs Adjustable Shunt Valves: How the Choice Is Made

A fixed-pressure shunt valve opens at one factory-set category, low, medium or high, that stays the same after implantation. An adjustable valve can have its setting changed afterwards without another operation. In the DESU range, Defit and Decurve are fixed-pressure only, Depus comes in fixed and adjustable forms, and adjustable Depus valves are set with the Depus Adjustment Kit. The final choice belongs to the surgeon.

The questions behind that choice map directly onto the shunt systems DESU manufactures in Ankara, Türkiye, and onto what neurosurgeons, theatre teams and hospital buyers decide to order and stock. For the engineering of adjustable valves themselves, see our article on adjustable shunt technology.

What is the difference between a fixed-pressure and an adjustable shunt valve?

Every shunt valve controls when cerebrospinal fluid (CSF) is allowed to leave the ventricles and flow to the drainage site, usually the peritoneal cavity. The difference between the two types is when the opening level is decided.

• Fixed-pressure valve: the pressure category is chosen before surgery, when the valve is ordered. If the surgeon later wants a different category, the valve has to be replaced.
• Adjustable valve: the same implanted valve can be moved between pressure levels from outside the body, using a dedicated tool set.

Which DESU valves are fixed and which are adjustable?

DESU makes three shunt valve families. Two are fixed-pressure only; one covers both routes.

• Defit: a fixed-pressure, flat-bottom silicone valve in Ultra Small, Small and Regular sizes (35, 40 and 45 mm overall length), with low, medium and high pressure options. It contains no metal and is suitable for MRI and CT.
• Decurve: a fixed-pressure, round burr-hole silicone valve with a reservoir, in a 23 mm paediatric and a 28 mm adult size, with low, medium and high options. It also contains no metal.
• Depus: a polysulfone valve with a ruby ball and titanium spring mechanism that opens automatically under positive ventricular pressure. It is offered in low, medium and high fixed pressures and as adjustable valves in paediatric and adult sizes, in ventriculoperitoneal (VP) and lumboperitoneal (LP) kits.

The VP kits share the same core components: the valve, a 23 cm ventricular catheter, a 120 cm peritoneal catheter, a stylet and a right-angled connector. All shunt systems are single-use and sterilised by ethylene oxide.

When is a fixed-pressure valve a reasonable choice?

Fixed-pressure valves remain widely used in hydrocephalus surgery. The question for the surgeon is whether one pressure category is likely to serve the patient well over time. Situations where a fixed valve often leads the discussion include:

• The surgeon is confident about the pressure category the patient needs, based on the clinical picture.
• The hospital prefers an implant with no follow-up hardware to manage, store or train staff on.
• Valve shape matters for placement: Defit’s flat-bottom body and Decurve’s burr-hole body are both fixed-pressure designs.
• A metal-free valve is preferred, which in the DESU range means Defit or Decurve.

Fixed valves also simplify ordering. A department can cover its needs with three pressure categories in the sizes it uses, without a separate accessory.

When does an adjustable valve make more sense?

The value of an adjustable valve is that a change of setting does not require a return to theatre. Over- and underdrainage are recognised concerns in shunt management, and a patient’s needs can change after implantation. Surgeons tend to consider an adjustable Depus valve when:

• The right pressure category is uncertain at the time of surgery.
• The team expects to fine-tune drainage as the patient recovers or as their condition changes.
• The surgeon wants the option of answering signs of over- or underdrainage by changing the setting rather than the valve.
• The hospital has, or will acquire, the matching Depus Adjustment Kit and staff familiar with it.

Adjustable Depus systems come in 3 Pressure and 5 Pressure versions. The choice between them is part of the same conversation: how many levels the surgeon wants available after implantation.

What does each option mean for follow-up?

With a fixed valve, there is nothing to read or set after surgery. The implanted pressure category is recorded in the patient’s implant documentation, and follow-up is clinical.

With an adjustable Depus valve, the setting becomes part of the patient’s record and of each follow-up visit. The Depus Adjustment Kit has three tools:

• Locator: identifies the valve and the target directions of the pressure levels.
• Magnet: sets the valve to the target pressure.
• Compass: checks the pressure level.

The kit is non-sterile and stored in a dedicated reusable case. It is offered in 3 Pressure and 5 Pressure versions, so the clinic needs the version that matches the implanted valve. Our article on adjustable VP shunts covers the adjustment workflow in more detail. Every step follows the instructions for use.

How do antisiphon, reservoir and antibiotic options fit in?

These options sit alongside the fixed-or-adjustable decision rather than replacing it:

• Antisiphon device: optional on Defit, Decurve and Depus VP kits, intended to prevent the siphon effect that can occur when the peritoneal catheter moves from horizontal to vertical. Kits that include it have a reference code ending in “-ASD”.
• Reservoir: built into the Decurve valve, and available as an add-on for Depus kits.
• Antibiotic-impregnated components: the antibiotic is impregnated into the material and released in a controlled manner over 28 days. Defit and Decurve are offered with valve-body-only impregnation, as semi-antibiotic kits (standard valve, impregnated catheters) and as full-antibiotic kits; Depus with impregnated ventricular and peritoneal catheters, and adjustable Depus valves also with an impregnated valve body. Impregnated catheters are orange, standard ones white.

What should a hospital keep in stock?

For a fixed-pressure programme, the stock plan is a grid: valve family, size and pressure category, with or without antisiphon and antibiotic options. For an adjustable programme, the plan adds the Depus Adjustment Kit in the version that matches the valves, kept where the follow-up clinic can reach it. Many neurosurgery departments keep both, so the valve follows the patient rather than the shelf. Our product specialists can help a department map its case mix to a practical starting range.

Talk to a DESU product specialist

If you are deciding between fixed-pressure and adjustable valves for a department or tender, a DESU product specialist can walk through the options and configurations with you. Write to sales@desu.tr, use the contact page, or request a quote.