Hydrocephalus: the zero ICP ventricle shunt (ZIPS) to control gravity shunt flow. A clinical study in 56 patients.
Significant morbidity from ventricle shunt overdrainage at 6-7 years after initial shunt placement for hydrocephalus is increasingly recognized as due to excessive gravity-flow of shunted CSF when upright. Shunts are designed primarily to control high ICP. Shunts should also mimic normal upright ICP. Normal upright ICP is -65 mm of water (vertex reference), indicating that a level of zero ICP exists at 65 mm below the brain vertex, with negative ICP above and positive ICP below that level. This normal zero ICP level must be maintained by CSF shunts to mimic normal upright ICP. This will prevent and correct CSF shunt overdrainage. The zero ICP shunt (ZIPS) by design controls this zero level with a zero pressure device (ZPD; siphon control device) installed at the normal vertical level of zero ICP (cm/mm) below the vertex (65 mm). The shunt thus prevents excessive gravity-induced CSF shunt flow. Successful use of ZIPS in 56 patients is reported (low ICP group: n = 42; high ICP group: n = 14). Follow-up is up to 4.5 years. Results show that: (1) adjustability of ZPD level can achieve the desired clinical results; (2) the level of ZPD installed correlates within 4 mm of upright ICP attained; (3) the optimal level of ZPD installation to produce normal upright ICP is 65 mm below the vertex; (4) CT ventricle size, both slit ventricles and large ventricles, may or may not normalize when normal upright ICP is attained in this group of complex, previously shunted patients.