Risks in using siphon-reducing devices in adult patients with normal-pressure hydrocephalus: bench test investigations with Delta valves

Abstract

To elucidate the reason for malfunction of Delta valves in patients with normal-pressure hydrocephalus, the authors applied a new concept of the bench test and simulated intracranial pressure (ICP) to measure the resultant flow with a complete shunt system. Subcutaneous pressure on the valve, valve implantation site, and postural hydrostatic differential-pressure changes were simulated in this bench test designed for adult patients with normal-pressure hydrocephalus. Subcutaneous pressure ranged within 6.4 +/- 0.09 cm H2O (mean +/- standard deviation) on the 7th day after the implantation of the valve in rats. A linear correlation between valve closing pressures and the external pressure was observed: gradual increase of the latter resulted in an approximately equal rise in the closing pressure. Closing pressure ranged within the physiological variation of ICP (10 +/- 5 cm H2O) in the supine position. In the erect position it was higher than the physiological variation (+5 to -5 cm H2O) when the valve was placed at the level of the foramen of Monro and lower when placed at the level of the clavicle. This observation indicates that the subcutaneous pressure around the Delta valve significantly affects its closing pressure. An excessive reduction of flow or a functional obstruction occurs when the patient with a Delta valve implanted at the foramen of Monro assumes an erect posture. The authors conclude that Delta valves are not recommended for implantation at the level of the foramen of Monro in patients with normal-pressure hydrocephalus because of the risk of underdrainage. The mastoid process or clavicle may be the alternative levels for its implantation to prevent underdrainage; however, the possibility of shunt malfunction should be kept in mind because subcutaneous pressure is variable among patients and that might affect the performance characteristics of these valves.

Infusion technique can be used to distinguish between dysfunction of a hydrocephalus shunt system and a progressive dementia

“…The pressure drop over the constriction and the pressure over the hydrocephalus shunt were measured with differential pressure transducers tt. The shunt was mounted on a support and submerged into 65 mm of water (HASSAN, et al, 1996) (corresponding to the tissue pressure). Outflow from the shunt was led into an overflow container with a constant water level at the zero pressure level, or at -3 kPa level when testing the anti-siphoning device with a distal hydrostatic component.…”

Clinical Experience With a Dual Switch Valve (Miethke) for the Management of Adult Hydrocephalus

“…The ASD requires precise location, 8,9) whereas the DSV can be implanted anywhere in parallel to the body axis. The present study indicates that the DSV prevents the majority of problems related to overdrainage.…”

Shunt assistant valve: bench test investigations and clinical performance

“…However, the antisiphon systems including the ASD, Delta valve, Novus valve and the Integra Referential valve as well as the new Strata valve carry a risk of underdrainage [3,6,10,17,20]. The causes of underdrainage are divided into two categories 1.…”

“…The causes of underdrainage are divided into two categories 1. Overfunction of the device, which is related to the position of the device [6,17,20] 2. Occlusion of device due to increased subcutaneous pressure around the device [3,6] The latter is the fatal disadvantage of the structure of this system.…”