The authors investigated and compared the in vitro characteristics of 2 CSF shunts, the Strata NSC and the Codman Hakim, and their corresponding antisiphon devices (ASDs).
Six new CSF shunts and the corresponding ASDs for each model were tested in an automated, computerized experimental setup based on pressure regulation. Opening pressure accuracy, resistance, sensitivity to abdominal pressure, antisiphon effect, and the influence of different ASD positions were determined.
In general the shunts performed according to the manufacturers' specifications. However, at the lowest setting, the opening pressure of the Strata NSC was close to 0, and in the Codman Hakim shunt, it was higher than specified. The resistance in the Codman Hakim shunt (5.4 mm Hg/ml/min) was much higher than that in the Strata NSC (3.6 mm Hg/ml/min). Abdominal pressure affected opening pressure in both valves. Positioning the Strata ASD above or below the ventricular catheter tip resulted in higher and lower opening pressures, respectively, than when it was placed in line with the catheter. The positioning of the Codman Hakim ASD did not influence the opening pressure.
Both CSF shunts work properly, but at the lowest setting the opening pressure of the Strata NSC was near 0 and in the Codman Hakim it was twice the manufacturer's specifications. The resistance in the Strata NSC was below the normal physiological range, and in the Codman Hakim device it was in the lower range of normal. The ASD did not change the shunt characteristics in the lying position and therefore might not do so in children. If this is the case, then a shunt system with an integrated ASD could be implanted at the first shunt insertion, thus avoiding a second operation and the possibility of infection.