Tag: Anti-siphon device

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In vitro performance of six combinations of adjustable differential pressure valves and fixed anti-siphon devices with and without vertical motion

Acta Neurochirurgica (2020) 162:2421–2430

Adjustable differential pressure (DP) valves in combination with fixed anti-siphon devices are currently a popular combination in counteracting the effects of cerebrospinal fluid overdrainage following implantation of a ventriculoperitoneal shunt system. The study examined the flowperformance of three DP valves in successive combination with an anti-siphon device in an in vitro shunt laboratory with and without vertical motion.

Methods We analyzed three DP valves (Codman Hakim Medos programmable valve [HM], Codman CertasPlus [CP], and Miethke proGAV [PG], in combination with either Codman SiphonGuard [SG] or Miethke ShuntAssistant [SA]), resulting in the evaluation of six different valve combinations. Defined DP conditions between 4 and 40 cmH2O within a simulated shunt system were generated and the specific flow characteristics were measured. In addition, combinations with SA, which is a gravitydependent valve, were measured in defined spatial positions (90°, 60°). All device combinations were tested during vertical motion with movement frequencies of 2, 3, and 4 Hz.

Results All valve combinations effectively counteracted the siphon effect in relation to the chosen DP. Angulation-related flow changes were similar in the three combinations of DP valve and SA in the 60° and 90° position. In CP-SA and PG-SA, repeated vertical movement at 2, 3, and 4 Hz led to significant increase in flow, whereas in HM-SA, constant increase was seen at 4 Hz only (flow change at 4Hz, DP 40 cm H2O: PG (opening pressure 4 cm H2O) 90°: 0.95 ml/min, 60°: 0.71 ml/min; HM (opening pressure 4 cmH2O) 90°: 0.66 ml/min, 60°: 0.41ml/min; CP (PL 2) 90°: 0.94ml/min, 60°: 0.79 ml/min; p < 0.01); however, HMSA showed relevant motion-induced flow already at low DPs (0.85 ml/min, DP 4 cm H2O). In combinations of DP valve with SG, increase of flow was far less pronounced and even led to significant reduction of flow in certain constellations. Maximum overall flow increase was 0.46 ± 0.04ml/min with aHM(opening pressure 12 cm H2O) at 2 Hz and a DP of 10 cmH2O, whereas maximum flow decrease was 1.12 ± 0.08 with a PG (opening pressure 4 cm H2O) at 3 Hz and a DP of 10 cmH2O.

Conclusion In an experimental setup, all valve combinations effectively counteracted the siphon effect in the vertical position according to their added resistance. Motion-induced increased flow was consistently demonstrated in combinations of DP valve and SA. The combination of HM and SA especially showed relevant motion-induced flow already at low DPs. In combinations of DP and SG, the pattern of the motion induced flow was more inconsistent and motion even led to significant flow reduction, predominantly at DPs of 10 and 20 cmH2O.

 

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Comparison of anti-siphon devices—how do they affect CSF dynamics in supine and upright posture?

Acta Neurochir (2017) 159:1389–1397

Three different types of anti-siphon devices (ASDs) have been developed to counteract siphoning induced overdrainage in upright posture. However, it is not known how the different ASDs affect CSF dynamics under the complex pressure environment seen in clinic due to postural changes. We investigated which ASDs can avoid overdrainage in upright posture best without leading to CSF accumulation.

Methods Three shunts each of the types Codman Hakim with SiphonGuard (flow-regulated), Miethke miniNAV with proSA (gravitational), and Medtronic Delta (membrane controlled) were tested. The shunts were compared on a novel in vitro setup that actively emulates the physiology of a shunted patient. This testing method allows determining the CSF drainage rates, resulting CSF volume, and intracranial pressure in the supine, sitting, and standing posture.

Results The flow-regulated ASDs avoided increased drainage by closing their primary flow path when drainage exceeded 1.39 ± 0.42 mL/min. However, with intraperitoneal pressure increased in standing posture, we observed reopening of the ASD in 3 out of 18 experiment repetitions. The adjustable gravitational ASDs allow independent opening pressures in horizontal and vertical orientation, but they did not provide constant drainage in upright posture (0.37 ± 0.03 mL/min and 0.26 ± 0.03 mL/min in sitting and standing posture, respectively). Consequently, adaptation to the individual patient is critical. The membrane-controlled ASDs stopped drainage in upright posture. This eliminates the risk of overdrainage, but leads to CSF accumulation up to the volume observed without shunting when the patient is upright.

Conclusions While all tested ASDs reduced overdrainage, their actual performance will depend on a patient’s specific needs because of the large variation in the way the ASDs influence CSF dynamics: while the flow-regulated shunts provide continuous drainage in upright posture, the gravitational ASDs allow and require additional adaptation, and the membrane-controlled ASDs show robust siphon prevention by a total stop of drainage.

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