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Biomedical subjects

R Bayston

Publications and source records attributed to R Bayston.

At least 37 records · Page 2Linked to original sources
PubMed1996

Removed shunt valves: reasons for failure and implications for valve design.

Most removed shunt valves are discarded with no investigation into why they had to be replaced or whether they still performed to specification. However, improvements in valve design will only occur if valves that have needed removal are examined and the reasons that they failed are determined. An in-depth study of 43 valves that were removed in this unit over a 15-month period was performed. They were submitted to a four-part study, comprising flow-pressure testing, opening and closing pressure measurement, assessment of the susceptibility to syphoning, and dismantling with internal inspection of the valve components. Overall, 81% of valves failed to meet the manufacturers' specified performance data, even though the peroperative cause of shunt failure was thought to lie outside the valve. Over 80% of valves with metallic parts were found to have accumulated debris internally, and this was thought to have impaired their performance. In contrast, only 25% of non-metallic 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 recommended that a change of valve should be considered in all shunt revisions, and that future valve designs should avoid metal components.

Cerebrospinal Fluid Pressure↗
PubMed1996

Does the cerebrospinal fluid protein concentration increase the risk of shunt complications?

A prospective study was performed to determine whether the popular opinion that a high CSF protein concentration increases the risk of shunt complications is true. Ninety-five patients were enrolled into the study and they had 116 shunt operations over 15 months. It was considered that the CSF protein content might influence the development of complications that occurred within 2 months of surgery. Shunt complications occurred following 24.6% of operations within this period. This included 12 infections, 13 obstructions and three cases of overdrainage. The distribution of complications, compared to CSF protein content, was non-significant on a chi 2-test (p > 0.5). The total protein content of each of the complication groups was also analysed using the Mann-Whitney U-test and the differences were non-significant for the infection (0.1 > p > 0.05) and obstruction groups (0.5 > p > 0.1). It is concluded that an elevated CSF protein content does not increase the risk of shunt complications, and that there is no reason why shunting should be delayed in patients with a high CSF protein content.

Adolescent↗
PubMed1996

The effect of protein and blood cells on the flow-pressure characteristics of shunts.

It has long been assumed that a high cerebrospinal fluid protein concentration adversely affects the performance of shunts. There is little experimental evidence to support this viewpoint, however, and the few reports that have been published can be criticized for poor experimental design or presentation of results. A flow-dependent shunt perfusion model was constructed. PS Medical Flow Control valves (PS Medical Corporation, Goleta, CA) and Cordis-Hakim valves (Cordis Corporates, Miami, FL) were perfused with saline-plasma solutions in concentrations from 0 to 9 g/L of protein. Blood suspensions in dilutions from 0.25 to 1% were also studied. The opening and closing pressures of the valves were measured with a simple manometer, and the physical properties of the solutions were studied. The results indicated that the valves performed within the ranges specified by their manufacturers, even with markedly increased protein concentrations in the perfusate. Furthermore, the valve opening and closing pressures were lower with the protein-containing solutions than with the control solutions. Thus, the protein did not impair shunt function and we conclude that shunts can be inserted into patients who have elevated cerebrospinal fluid protein contents. However, blood cells did adversely affect performance and, therefore, patients with hemorrhagic cerebrospinal fluid should not receive shunts.

Cerebrospinal Fluid Pressure↗
PubMed1996

Reduced bacterial adhesion to hydrocephalus shunt catheters mediated by cerebrospinal fluid proteins.

BACKGROUND: Prosthetic infections are a major problem, requiring complex and lengthy management. The role of blood proteins in the pathogenesis of implant infection has been investigated, but research into the role of CSF protein in shunt infections has not been undertaken, even though a high CSF protein has been assumed to increase the risk of such infections. METHODS: New shunt catheters were exposed to either CSF or individual protein solutions, and the numbers of radiolabelled staphylococci that adhered to them were compared with controls that had been exposed to saline only. RESULTS: A significant reduction in bacteria adhering to the test catheter was found in each instance. Furthermore, the CSF with the highest protein content, from a patient with intraventricular haemorrhage, had the greatest inhibitory effect on bacterial adhesion. The effect of the solutions on the hydrophobicity of the silicone rubber was also investigated. The silicone rubber was more hydrophilic, and bacterial adhesion was less, with solutions containing a higher protein content, and these findings were in keeping with the current theories on the mechanism of bacterial adhesion to polymers. CONCLUSIONS: A high CSF protein content does not predispose to the development of shunt infections.

Bacterial Adhesion↗
PubMed1995

Physical properties of cerebrospinal fluid of relevance to shunt function. 1: The effect of protein upon CSF viscosity.

Viscosity is the resistance to flow of a fluid and it is the only property of a fluid that will affect its flow through a system of valveless tubing (surface tension will affect the opening and closing of valves that are included in the system). The effect that an elevated protein concentration has upon CSF viscosity has received little study, yet many neurosurgeons believe that CSF with an elevated protein content is too viscous to flow satisfactorily through shunts. The total protein content and viscosity of 126 specimens of CSF from hydrocephalic patients were measured and analysed with reference to the aetiology of the hydrocephalus. The results indicate that high protein concentrations do not greatly affect the viscosity of CSF, and that the aetiology is also of little consequence. These findings were highly significant on linear regression analysis (p < 0.001). The flow of the most viscous CSF that is likely to be encountered would be reduced by only 7% through a given catheter, compared with that of the least viscous CSF.

Adolescent↗
PubMed1995

Physical properties of cerebrospinal fluid of relevance to shunt function. 2: The effect of protein upon CSF surface tension and contact angle.

CSF surface tension has received little study, and yet it will effect the pressure at which shunt valves operate, and by influencing the degree of hydrophobicity (contact angle) will alter the attraction between bacteria and neurosurgical prostheses. A study is therefore presented of the effect of protein content upon the surface tension of CSF and its contact angle to silicone rubber. Both of these quantities fell throughout the normal range of CSF protein, but above 1 g/l, additional protein had little effect, and the results obtained were similar to that reported for plasma. The effect of surface tension on the opening and closing pressures of hydrocephalus shunt valves and of contact angle in the adhesion of bacteria to neurosurgical implants is discussed.

Adolescent↗
PubMed1994

Role of serological tests in the diagnosis of immune complex disease in infection of ventriculoatrial shunts for hydrocephalus.

Seven cases of ventriculoatrial shunt infection with immune complex disease are reported in order to demonstrate the usefulness of measurement of levels of specific antibody to Staphylococcus epidermidis in diagnosis. Blood and cerebrospinal fluid cultures gave misleading results, and there was initial doubt about the diagnosis in all seven cases. All showed grossly elevated titres of antibody to Staphylococcus epidermidis, with raised serum C-reactive protein levels and depressed complement levels. Measurement of antibody to Staphylococcus epidermidis enables the diagnosis of chronic ventriculoatrial shunt infection to be made rapidly and reliably.

Adolescent↗
PubMed1994

Cerebrospinal fluid shunt infection due to Corynebacterium xerosis.

We report the case of a neonate who developed ventriculitis following insertion of a ventriculoperitoneal shunt. Corynebacterium xerosis was isolated from CSF and from the tip of the catheter after it was removed. The isolate was resistant to multiple antibiotics, but the infant responded to treatment with vancomycin.

Ciprofloxacin↗
PubMed1994

Hydrocephalus shunt infections.

Hydrocephalus is most commonly diagnosed in the first few months of life, though cases also arise in later life. Cerebrospinal fluid shunts used to control the condition are prone to colonization particularly by Staphylococcus epidermidis. The incidence is very much higher in infancy than in older age groups, and this is probably due to prolonged hospital stay as a result of the underlying pathology, combined with the propensity for a high skin bacterial density with more adherent strains, rather than to any immune immaturity. Diagnosis of shunt colonization is often very difficult and serological tests have an important role to play even in infancy. There are several pitfalls in diagnosis, particularly in the elderly. Treatment of shunt infections should include removal of the colonized shunt, though regimens to avoid this are currently being investigated. Intraventricular therapy with vancomycin along with intravenous rifampicin offers the best changes of success at the first attempt. Shunted patients who contract purulent bacterial meningitis should not have their shunts removed but should be treated in the same way as those without shunts.

Adult↗
PubMed1994

Production of extracellular slime by coryneforms colonizing hydrocephalus shunts.

Corynebacterium spp. are responsible for an important minority of cases of colonization of cerebrospinal fluid shunts used for the treatment of hydrocephalus. In common with coagulase-negative staphylococci, they present a serious therapeutic problem because they are often resistant to multiple antibiotics. We studied the morphologies of coryneforms in colonized hydrocephalus shunts removed from patients and observed extracellular slime similar in appearance to that seen in coagulase-negative staphylococci. We also studied a series of such isolates from other cases of hydrocephalus shunt colonization using an established laboratory model and consistently observed slime production in these shunts as well. We propose that this might be a further reason for failure to eradicate these organisms without shunt removal as well as a factor in their pathogenesis in device-related infections.

Adult↗
PubMed1994

An evaluation of the epileptogenic properties of a rifampicin/clindamycin-impregnated shunt catheter.

A process has been developed by which ventriculoperitoneal hydrocephalus shunts, which are prone to bacterial colonisation, can be impregnated with antimicrobials in order to confer antibacterial activity. Concern that their use might be associated with an increased risk of postoperative seizures has been addressed here. Using two rat models, namely pentylenetetrazole (PTZ) and maximal electroconvulsive seizure (ECS) thresholds, the possible epileptogenic characteristics of the shunt catheters were determined. Animals implanted with impregnated catheters exhibited no significant difference in PTZ seizure threshold compared with controls. In contrast, the ECS threshold test showed an enhancement in seizure susceptibility in the non-impregnated catheter group, in accordance with that found in human subjects, but a significant reduction in the impregnated catheter group at 2 and 28 days, postoperatively. These data suggest that the use in human subjects of shunts impregnated with these antimicrobials will not increase the risk of postoperative seizures.

Animals↗
PubMed1993

Serological response to coagulase-negative staphylococci in patients with peritonitis on continuous ambulatory peritoneal dialysis.

Sera and dialysis effluent from 20 patients on continuous ambulatory peritoneal dialysis (CAPD) with coagulase-negative staphylococcal (CNS) peritonitis were examined by immunoblotting for antibody activity against CNS. Immunoblotting was highly sensitive and demonstrated significantly greater antibody activity in serum and dialysate of infected patients compared with that of uninfected CAPD patients or healthy volunteers. Fourteen of 20 infected CAPD patients had strong antibody activity (> 7 bands); one patient had equivocal activity. Five patients had weak antibody activity, two of whom suffered from recurrent peritonitis with distinguishable CNS strains despite a satisfactory CAPD technique. One patient with a poor CAPD technique had strong antibody activity, but suffered from recurrent peritonitis. Examination of sequential sera suggested that seroconversion occurred soon after insertion of the Tenckhoff catheter, possibly in the absence of clinical infection. Antibody activity against a 25 kDa staphylococcal protein was significantly associated with peritonitis.

Antibodies, Bacterial↗
PubMed1993

Prolonged carriage of Clostridium difficile in Hirschsprung's disease.

The role of Clostridium difficile in the aetiology of diarrhoea in children with Hirschsprung's disease was investigated in a prospective longitudinal study. In 64 children with Hirschsprung's disease no significant difference was found in the isolation rate of C difficile in patients with diarrhoea (32%) and without diarrhoea (26%). Comparable isolation rates were found in 47 control children with and without diarrhoea (27% and 16% respectively). The number of strains producing toxin B was similar in the four groups of children. In contrast to the disappearance of C difficile by 12 months of age in the control groups of children, C difficile could be repeatedly isolated from a proportion of children with Hirschsprung's disease over 12 months of age. These findings help to reconcile the existing contradictory reports on the incidence of C difficile in Hirschsprung's disease associated enterocolitis.

Adolescent↗
PubMed1993

Electrogenic colonic ion transport in Hirschsprung's disease: reduced secretion to the neural secretagogues acetylcholine and iloprost.

The effects of the abnormal innervation in Hirschsprung's disease on colonic ion transport were examined in vitro using Ussing chambers. The response of the mucosal/submucosal preparations to different secretagogues were investigated in aganglionic and ganglionic rectosigmoid and transverse colon from children with Hirschsprung's disease and compared with normally innervated colon from children with anorectal anomalies. Basal values were similar in aganglionic and ganglionic rectosigmoid colon. Neurally mediated secretion with iloprost (10(-6) M) and acetylcholine (900 and 9 microM) was considerably reduced in aganglionic colon compared with normally innervated ganglionic colon. The ganglionic colon proximal to the aganglionic colon also had a reduced response to acetylcholine despite a normal acetylcholinesterase staining pattern. The responses to Escherichia coli STa enterotoxin (50 MU/ml) and isobutylmethylxanthine (10(-3) M) were similar in ganglionic and aganglionic colon. The response to STa enterotoxin was not changed by the nerve blocking agent tetrodotoxin (10(-6) M). The data show that colonocytes from aganglionic colon are capable of a normal secretory response if stimulated directly by cAMP or cGMP acting secretagogues but secretion in response to neurally mediated secretagogues is impaired. The hypertrophied acetylcholinesterase positive nerve fibres that infiltrate the aganglionic colon are likely to contribute to the reduced secretion to acetylcholine.

1-Methyl-3-isobutylxanthine↗