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

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.For settings 1–7 the measured opening pressure range was 26 to 247 mmH2O, and the mean change in opening pressure for a one-step adjustment was between 33 and 38 mmH2O. For setting 8 (“Virtual Off”) the measured mean opening pressure was 494？±？34 mmH2O (range 451 to 556 mmH2O). The mean outflow resistance was 7.0？mmHg/ml/min (outflow conductance 17.9 μl/s/kPa).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 mmH2O, which is 100 mmH2O 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.Improvements in the modern shunt for drainage of cerebrospinal fluid (CSF) in the surgical treatment of hydrocephalus have aimed to include features in shunt design that reduce complications and improve clinical outcome. One goal has been to increase control over the amount of CSF drainage, such as adjustable shunt valves that permit postoperative adjustment of the shunt valve opening pressure. Several different brands of adjustable CSF shunts are available, characterized by opening pressures ranging from approximately 0 to 200？mm H2O, depending on the brand and the model. If a patient’s clinical response after shunt surgery is inadequate, lowering the shunt valve opening pressure may improve outcome while avoiding surgery to remove and replace the shunt valve. Alternately, in patients with over-drainage symptoms of headache or hearing change, or signs such as subacute or chronic subdural