Objective: Infants and small children face changing boundary conditions when treated with a ventriculoperitoneal shunt (VPS) for hydrocephalus. There are no systematic data describing shunt drainage behavior and changes over time in a growing child. Using a child-adapted patient simulator, the authors investigated the drainage behaviors of fixed differential pressure (DP) valves and adjustable valves with devices for preventing overdrainage in children of different ages.
Methods: Three miniNAV DP valves with a 10-cm H2O medium-pressure setting (MN10) and three adjustable proGAV2.0 valves with a 25-cm H2O gravitational unit (GU) at low 5-cm H2O opening pressure (PG5) and medium 10-cm H2O opening pressure (PG10) settings were each investigated with a hardware-in-the-loop test bed. This test bed consisted of a posture motion mechanism and two pressure compartments that mimicked intracranial and abdominal pressures and was used to test the VPS under realistic in vitro conditions. Body orientation and length were physically set according to the child's age. The software simulated the physiological situations of children aged 1, 5, and 10 years. All valves were tested according to these specifications, with 5 runs for 1 hour each in the horizontal, vertical, and horizontal positions. Intracranial pressure (ICP) and VPS flow were measured, and the respective cerebrospinal fluid volume changes and ICP set value were computed.
Results: The drainage parameters increased with age in all valves in the vertical position, with that of MN10 being pronounced in the 1-year-old simulation. The GU values in PG5 and PG10 substantially reduced drainage compared with MN10. PG10 prevented drainage in the 1-year-old and 5-year-old setups, but there was some drainage at physiological ICP in the 10-year-old setup. In contrast, MN10 produced the largest decreases in ICP across all ages and positions, and overdrainage resulted in insufficient ICP recovery in the subsequent horizontal position. ICP levels were mostly constant with PG10 at all ages.
Conclusions: This study shows that unprotected DP valves may lead to overdrainage in infants, whereas low-pressure GU valves can prevent overdrainage through 5 years and medium-pressure GU valves admit physiological ICP through at least 10 years. Therefore, devices for preventing overdrainage should be included in the first implanted shunt, and opening pressure should be adjusted as the child grows.
Keywords: differential pressure valve; hardware-in-the-loop testing; overdrainage syndrome; pediatric hydrocephalus; ventriculoperitoneal shunt.