In vitro performance of combinations of anti-siphon devices with differential pressure valves in relation to the spatial position.

BACKGROUND: Programmable differential pressure (DP) valves combined with an anti-siphon device (ASD) represent the current standard of care in preemtping overdrainage associated with ventriculoperitoneal shunting for hydrocephalus. OBJECTIVE: We aimed to provide comparative data of four combinations of two ASDs of different working principles in combination with two DP valves in an in vitro model in order to achieve a better understanding of the flow characteristics and potential clinical application. METHODS: We analyzed the flow performance of four possible combinations of two DP valves (CHPV [HM]; proGAV 2.0[PG]) in combination with either a gravity-regulated (Shuntassistant [SA]) or a flow-regulated (SiphonGuard [SG]) ASD in an in vitro setup. A DP between 4 and 60 cmH2O was generated, and the specific flow characteristics were measured. In addition, the two combinations with gravity-regulated ASDs were measured in defined spatial positions. RESULTS: Flow characteristics of the SA combinations corresponded to the DP in linear fashion and to the spatial position. Flow characteristics of the SG combinations were dependent upon the DP in a non-linear fashion and independent of the spatial position. Highest mean flow rate of the PG-SG- (HM-SG-) combination was 1.41 ± 0.24 ml/min (1.16 ± 0.06 ml/min). The mean flow rates sharply decreased with increasing inflow pressure and subsequently increased slowly up to 0.82 ± 0.26 ml/min (0.77 ± 0.08 ml/min). CONCLUSION: All tested device combinations were able to control hydrostatic effect and prevent consecutive excessive flow, to varying degrees. However, significant differences in flow characteristics can be seen, which might be relevant for their clinical application.

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

OBJECTIVE: 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 flow performance 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 cm H2O within a simulated shunt system were generated and the specific flow characteristics were measured. In addition, combinations with SA, which is a gravity-dependent 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 cm H2O) 90°: 0.66 ml/min, 60°: 0.41 ml/min; CP (PL 2) 90°: 0.94 ml/min, 60°: 0.79 ml/min; p < 0.01); however, HM-SA 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 ± 0.04 ml/min with a HM (opening pressure 12 cm H2O) at 2 Hz and a DP of 10 cm H2O, 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.

Efficacy and safety of durotomy after decompressive hemicraniectomy in traumatic brain injury.

Decompressive hemicraniectomy (DH) plus duroplasty was demonstrated to be effective for treating critically elevated intracranial pressure (ICP). In order to shorten operation time and to avoid the use of autologous or heterologous material, durotomy has been introduced as an alternative to duroplasty. Only limited data is available on the effect of DH and durotomy on the increased ICP in traumatic brain injury (TBI). Therefore, we collected consecutive intraoperative ICP readings during the different steps of DH and durotomy in TBI patients. Eighteen patients with TBI and uncontrollable ICP increase (measured by either an intraparenchymal or an intraventricular ICP probe) underwent DH and durotomy. ICP readings as well as mean arterial blood pressure (MAP) and arterial PCO2 were obtained during defined stages of the operation. Surgical complications of the durotomy itself and of cranioplasty after 3 months were recorded. The outcome was assessed prior to cranioplasty using the Glasgow Outcome Scale (GOS). ICP dropped significantly during surgery from a mean of 41 ( ± 16.2) mmHg at the beginning to a mean of 11.8 ( ± 7.5) mmHg at the end (p ≤ 0.001). A first significant ICP-decrease to a mean of 18 ( ± 10.8) mmHg (p ≤ 0.001) was detected after removal of the bone flap, and a second significant ICP-decrease to a mean of 10.6 ( ± 5.3) mmHg (p < 0.001) during durotomy. The mean operation time was 115.3 min ( ± 49.6). Five patients (28%) died; seven patients (39%) had a good outcome (GOS 5). There were no relevant complications associated to durotomy. Durotomy after DH is a safe and straightforward procedure, which significantly lowers critically increased ICP in patients with TBI. Although no graft is used, dural preparation for cranioplasty at 3 months is easily possible.