REMOVED SHUNT VALVES - REASONS FOR FAILURE AND IMPLICATIONS FOR VALVEDESIGN

Most removed shunt valves are discarded with no investigation into why they had to be replaced or whether they still performed to specificat ion. However, improvements in valve design will only occur if valves t hat have needed removal are examined and the reasons that they failed are determined. An in-depth study of 43 valves that were removed in th is unit over a 15-month period was performed. They were submitted to a four-part study, comprising flow-pressure tearing, opening and closin g pressure measurement, assessment of the susceptibility to syphoning, and dismantling with internal inspection of the valve components. Ove rall, 81% of valves failed to meet the manufacturers' specified perfor mance data, even though the peroperative cause of shunt failure was th ought to lie outside the valve. Over 80% of valves with metallic parts were found to have accumulated debris internally, and this was though t to have impaired their performance. Ln contrast, only 25% of non-met allic valves contained debris, a significant difference (0.01 > p > 0. 001). All of the valves had a high tendency to overdrainage. Attention is drawn to the high number of malfunctioning valves. It is recommend ed that a change of valve should be considered in all shunt revisions, and that future valve designs should avoid metal components.