Flow-related noise in patients with ventriculoperitoneal shunt using gravitational adjustable valves.

BACKGROUND: Noise disturbance arising from the valve is a rare event of ventriculoperitoneal shunts. We queried and investigated shunt patients for occurrence and evaluated the possible factors related to noise development. METHODS: Fifty ambulatory patients with implanted proGAV valve were investigated consecutively. Patients were asked for any noise arising from the shunt. In all cases, the valve was auscultated in sitting and upright position. The position of the gravitational unit (GU) was determined in respect to the Frankfurt horizontal plane (FHP) and in head reclination. Ten valves were perfused in vitro at different settings. One valve was opened for video documentation, and a frequency analysis of the noise was performed in nine valves. RESULTS: Eight percent (4/50) of the patients reported a noise arising from the valve only in upright position in combination with maximum head reclination, and immediately stopped when performing Vasalva's maneuver. In three out of four of these patients, the noise was also audible for the investigator (FS) with a prepared stethoscope. Patients complaining about a noise had a larger GU deviation from vertical during head reclination (median: -80 vs -43°, p = 0.0007, t-test). A deviations threshold of less than -58.4° excluding audible noise by a negative predictive value of 1 (95 % confidence interval [CI] 0.9 to 1.0). In an experimental setting, the noise came from vibrations of the ball in the cone of the adjustable unit and was restricted to a flow of at least 220 ml/h. The noise frequencies tended to be higher at higher opening pressures. CONCLUSIONS: Valve-related noise development may occur in patients with proGAV valves. This event could be prevented during shunt placement by avoiding posterior tilt of the gravitational unit, especially in patients with a good cervical mobility. The noise might indicate transient peak flows and was not associated with clinical or radiological signs of overdrainage.