Hydrodynamics of the Certas™ programmable valve for the treatment of hydrocephalus

Background: The new Certas™ shunt for the treatment of hydrocephalus has seven standard pressure settings that according to the manufacturer range from 36 to 238 mmH ₂O, and an additional " Virtual Off" setting with an opening pressure >400 mmH ₂O. Information on actual pressure response and reliability of shunt performance is important in clinical application, especially the " Virtual Off" setting as a non-surgical replacement for shunt ligation. The objective of this study was to evaluate the in-vitro hydrodynamic performance of the Certas™ shunt.Methods: Six new Certas™ shunts with proximal and distal catheters were tested with an automated, computerized test system that raised the pressure from zero to a maximum pressure and back to zero at each valve setting. Opening pressure and flow resistance were determined.Results: For settings 1-7 the measured opening pressure range was 26 to 247 mmH ₂O, and the mean change in opening pressure for a one-step adjustment was between 33 and 38 mmH ₂O. For setting 8 (" Virtual Off" ) the measured mean opening pressure was 494 ± 34 mmH ₂O (range 451 to 556 mmH ₂O). The mean outflow resistance was 7.0 mmHg/ml/min (outflow conductance 17.9 μl/s/kPa).Conclusions: The six shunts had similar characteristics and closely matched the manufacturer's specifications for opening pressure at settings 1-7. The opening pressure for the " Virtual Off" setting was nearly 500 mmH ₂O, which is 100 mmH ₂O higher than the manufacturer's specification of " >400" and should be functionally off for most patients with communicating hydrocephalus. Clinical studies are needed to evaluate if the CSF dynamic profile persists after implantation in patients.