Bolt Intracranial Pressure Monitoring, EVD or Probe: How to Choose

How each device works

An EVD is a catheter placed into the lateral ventricle and connected to a fluid-filled line with an external transducer, usually levelled at a defined anatomical reference. The same catheter can drain CSF through a collection system. In a bolt-based system, a hollow bolt is screwed into a burr hole, and an intracranial probe, commonly fibre-optic or strain-gauge, is passed through it into the parenchyma or subdural space.

A tunnelled intraparenchymal probe without a bolt is also used. The choice of device is made by the neurosurgeon according to the clinical question; equipment buyers should understand the kit differences listed below.

• EVD: catheter, fluid line, external transducer, drainage bag
• Bolt kit: hollow bolt, probe, cable, monitor interface
• Both: sterile insertion set, zeroing instructions, connection to bedside monitor

Which intracranial pressure monitoring device allows drainage and sampling?

Only the EVD. Because the catheter lies in the ventricle and is open to a fluid line, it can lower pressure by draining CSF and can be used to take samples or give intrathecal medication where the protocol allows. A parenchymal or subdural probe is a closed sensor: it reports pressure, but cannot treat it.

For this reason many neuro-ICUs place an EVD when hydrocephalus or CSF diversion is expected and choose a probe when pressure data alone are sufficient or when the ventricles are small.

In some cases both are used together: an EVD for drainage and a separate probe for a pressure reading that remains reliable while the drain is open. This adds consumable cost and an extra procedure, so it is a clinical decision rather than a default.

Accuracy, drift and infection risk

Fibre-optic and strain-gauge probes are zeroed before insertion, and some types cannot be re-zeroed in place, so a small drift over days is possible. An EVD with an external transducer can be re-zeroed and levelled at the bedside but is sensitive to patient position, air bubbles and catheter occlusion, and readings may be lost when the drain is open.

Infection risk is generally reported as higher with ventricular catheters than with parenchymal probes, rising with the duration of use, which is why protocols focus on sterile technique and early removal. Always base choices on current guidelines and the manufacturer's instructions; our overview of ICP monitoring devices places these options in a broader context.

Kit contents, cost and training

An intraparenchymal ICP monitoring kit contains the probe, bolt, a drill bit sized for the bolt and often a cable to the monitor module. The probe is usually single-use, so ongoing consumable cost is the main budget item. EVD kits have lower unit cost but need drainage systems and nursing time for care.

Whichever you choose, train nurses on levelling, transducer zeroing and calibration and waveform recognition, and make sure your bedside monitors have the right ICP channel. Normal ranges and waveform patterns are in normal ICP values and waveforms.

Making the choice and sourcing equipment

The comparison table to build with your clinicians covers drainage need, expected duration, local infection data, consumable cost and monitor compatibility. For non-invasive adjuncts see invasive versus non-invasive ICP monitoring.

Beckfinity supplies critical-care and neurosurgery equipment to UAE hospitals. To discuss your monitoring set-up, contact our specialists.