Programmable vs. Fixed Pressure Valves: Key Differences

What Are Programmable and Fixed Pressure Valves?

When a shunt is placed to manage cerebrospinal fluid (CSF) drainage, a valve is an essential component that controls the flow of fluid out of the brain. The valve ensures that CSF is flows in one direction and tries to manage the drainage at the correct rate to maintain a healthy balance—not too much and not too little.

There are two main types of valves: fixed pressure valves and adjustable (programmable) valves. The key difference between them lies in their ability to adjust drainage settings after implantation. Both of these employ a mechanism that opens the valve at a defined pressure difference between the brain and the end of the shunt – so they are sometimes called ‘differential pressure’ valves. They should ‘open’ when the pressure difference at the head and the other end of the shunt reaches a defined amount.

What Is a Fixed Pressure Valve?

A fixed pressure valve operates at a pre-set pressure level, meaning the pressure the shunt opens at (and thus the resistance to CSF flow) is chosen at surgery and cannot be changed once the valve is surgically placed. It is designed to maintain a consistent level of drainage based on the selected pressure setting, which can be low, medium, high or very high.

When and Why Is It Used?

• Used in patients who do not require adjustments (see below).
• The majority of patients implanted with this type of valve rarely require any change to a valve (a pressure change); the needed pressure is usually predictable.

What Is an Adjustable (Programmable) Valve?

An adjustable (programmable) valve allows doctors to adjust the opening pressure without a surgery (non-invasively) after implantation.  This is done with an external magnetic device (specific to the make of the valve). This valve allows for flexibility in changing the valve pressure to meet the patient’s evolving needs over time.

NOTE: Care must be taken to keep toys with magnets and other sources of magnetic fields away from the implanted device. It’s important to ask your doctor what precautionary measures should be taken.

When and Why Is It Used?

• Selected when CSF drainage needs may change, such as when the ventricles are extremely large and the drainage needs will change as the size decreases
• Useful for those who have had prior shunt complications, such as overdrainage or underdrainage, requiring different pressure settings over time, and the needed pressure is hard to define in advance of the surgery.
• Often recommended for patients with complex hydrocephalus management needs, where fine-tuning CSF flow can improve outcomes.
• Some of these valves will need to be checked after any magnetic resonance scan.

Choosing the Right Valve: Stability vs. Flexibility

Both types of valves serve the same purpose—regulating CSF drainage to prevent complications.

A fixed pressure valve provides simplicity and reliability, while an adjustable (programmable) valve allows for flexibility and adjustments over time.

The decision on which valve to use depends on factors such as how stable the drainage needs are, the potential need for future adjustments, and lifestyle considerations. Patients and caregivers should discuss these options with their neurosurgeon to determine the best fit based on individual needs.

Visual Guide: Valves from Different Shunt Manufacturers

Shunt manufacturers offer various programmable and fixed pressure valves. The following table below shows examples from different companies, illustrating their designs.

To see the full product listing for each company, click on their logo.

	M.blue™ Adjustable Valve
	Codman® Certas™ Plus
	OSV II® Flow Regulating Valve
	Strata Adjustable Valve
	Novus™ Valve
	Polaris Adjustable Valves numerous configurations available

Information you can trust! This article was produced by the Hydrocephalus Association, copyright 2025. We would like to thank Bruce A. Kaufman, MD for his valuable contribution and expert input.

This article is designed to provide helpful information on the subjects discussed. It is not intended as a substitute for treatment advice from a medical professional. For diagnosis or treatment of any medical condition, consult your doctor.