In vitro performance and principles of anti-siphoning devices

Anti-siphon devices (ASDs) of various working principles were developed to overcome overdrainage-related complications associated with ventriculoperitoneal shunting. We aimed to provide comparative data on the pressure and flow characteristics of six different types of ASDs (gravity-assisted, membrane-controlled, and flow-regulated) in order to achieve a better understanding of these devices and their potential clinical application. We analyzed three gravity-dependent ASDs (ShuntAssistant [SA], Miethke; Gravity Compensating Accessory [GCA], Integra; SiphonX [SX], Sophysa), two membrane-controlled ASDs (Anti-Siphon Device [IASD], Integra; Delta Chamber [DC], Medtronic), and one flow-regulated ASD (SiphonGuard [SG], Codman). Defined pressure conditions within a simulated shunt system were generated (differential pressure 10-80 cmH(2)O), and the specific flow and pressure characteristics were measured. In addition, the gravity-dependent ASDs were measured in defined spatial positions (0-90A degrees). The flow characteristics of the three gravity-assisted ASDs were largely dependent upon differential pressure and on their spatial position. All three devices were able to reduce the siphoning effect, but each to a different extent (flow at inflow pressure: 10 cmH(2)O, siphoning -20 cmH(2)O at 0A degrees/90A degrees: SA, 7.1 A +/- 1.2 /2.3 A +/- 0.5 ml/min; GCA, 10.5 A +/- 0.8/3.4 A +/- 0.4 ml/min; SX, 9.5 A +/- 1.2 /4.7 A +/- 1.9 ml/min, compared to control, 11.1 A +/- 0.4 ml/min [ p < 0.05]). The flow characteristics of the remaining ASDs were primarily dependent upon the inflow pressure effect (flow at 10 cmH2O, siphoning 0 cmH(2)O/ siphoning -20cmH(2)O: DC, 2.6 A +/- 0.1/ 4 A +/- 0.3 ml/min; IASD, 2.5 A +/- 0.2/ 0.8 A +/- 0.4 ml/min; SG, 0.8 A +/- 0.2 / 0.2 A +/- 0.1 ml/min [ p < 0.05 vs. control, respectively]). The tested ASDs were able to control the siphoning effect within a simulated shunt system to differing degrees. Future comparative trials are needed to determine the type of device that is superior for clinical application.