From the Guidelines
Ventriculoperitoneal (VP) shunts are adjusted by neurosurgeons using specialized magnetic devices to change the pressure setting of programmable valves, with settings confirmed and potentially reset after MRI scans to prevent under- or over-draining, as emphasized in the 2019 guidelines from the Association of Anaesthetists and the Neuro Anaesthesia and Critical Care Society of Great Britain and Ireland 1. The adjustment process involves careful assessment and planning, particularly for patients with programmable shunts, to ensure that the pressure settings are appropriate and do not lead to complications such as under- or over-draining of cerebrospinal fluid. Key considerations in the adjustment of VP shunts include:
- The use of MRI scans, which can alter the pressure settings on valves of programmable shunts, necessitating assessment by the neurosurgical team before and after scanning 1.
- The importance of verifying the correct settings after exposure to strong external magnetic fields, such as those from MRIs or certain electronic devices.
- Monitoring of symptoms like headaches, vision changes, or balance issues to determine the need for adjustment, indicating potential over- or under-drainage of cerebrospinal fluid. Adjustments are typically made in clinical settings using fluoroscopy or X-rays to confirm the new setting, and are non-invasive and painless, taking only minutes to perform. However, patients may need to lie flat for a period afterward to allow pressure stabilization. The specific details of the adjustment process, including the type of programmable valve used (e.g., Codman Hakim, Medtronic Strata, Sophysa valves) and the pressure ranges (typically between 30-200 mm H2O), are determined on a case-by-case basis by the neurosurgical team.
From the Research
Adjustment of Ventriculoperitoneal (VP) Shunts
- Ventriculoperitoneal (VP) shunts are programmable, allowing clinicians to adjust valve-pressure according to individual patient needs 2.
- The adjustment of VP shunts can be done reactively to avoid over- and under-drainage or planned to achieve optimal results 2.
- Studies have shown that most patients require one or two adjustments of their valve-pressures for optimal results, with optimal valve-pressure for most patients being around 50 mmH2O 2.
Methods of Adjustment
- Valve-pressure can be adjusted by manually changing the settings on the programmable valve 2, 3.
- The goal of shunt therapy is usually to achieve valve-pressure settings between 30 and 70 mmH2O 2.
- Adjustments can be made to address symptoms such as headaches, vertigo, or the development of subdural hygroma 2.
Considerations for Adjustment
- The use of adjustable-pressure valves (APVs) has been shown to have a lower rate of surgical revisions compared to differential-pressure valves (DPVs) 4.
- The adjustment of VP shunts should be done with caution, as exposure to powerful magnetic fields, such as those generated by transcranial magnetic stimulation (TMS), can alter the settings of programmable valves or cause permanent damage 5.
- MRI-based diagnostic schemes can be useful in determining the optimal valve-pressure settings for patients with idiopathic normal pressure hydrocephalus (iNPH) 6.