Silicone Rubber Catheters Research Articles

Generalized Multifunctional Coating Strategies Based on Polyphenol-Amine-Inspired Chemistry and Layer-by-Layer Deposition for Blood Contact Catheters.

Blood-contacting catheters play a pivotal role in contemporary medical treatments, particularly in the management of cardiovascular diseases. However, these catheters exhibit inappropriate wettability and lack antimicrobial characteristics, which often lead to catheter-related infections and thrombosis. Therefore, there is an urgent need for blood contact catheters with antimicrobial and anticoagulant properties. In this study, we employed tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) to create a stable hydrophilic coating under mild conditions. Heparin (Hep) and poly(lysine) (PL) were then modified on the TA-APTES coating surface using the layer-by-layer (LBL) technique to create a superhydrophilic TA/APTES/(LBL)4 coating on silicone rubber (SR) catheters. Leveraging the superhydrophilic nature of this coating, it can be effectively applied to blood-contacting catheters to impart antibacterial, antiprotein adsorption, and anticoagulant properties. Due to Hep's anticoagulant attributes, the activated partial thromboplastin time and thrombin time tests conducted on SR/TA-APTES/(LBL)4 catheters revealed remarkable extensions of 276 and 103%, respectively, when compared to uncoated commercial SR catheters. Furthermore, the synergistic interaction between PL and TA serves to enhance the resistance of SR/TA-APTES/(LBL)4 catheters against bacterial adherence, reducing it by up to 99.9% compared to uncoated commercial SR catheters. Remarkably, the SR/TA-APTES/(LBL)4 catheter exhibits good biocompatibility with human umbilical vein endothelial cells in culture, positioning it as a promising solution to address the current challenges associated with blood-contact catheters.

Effect of ionizing radiation on the physicochemical and functional properties of silicone rubber and silicone foley catheter

The utilization of ionizing radiation, such as gamma ray and electron beam, in medical product sterilization has seen significant growth in recent years, driven by concerns regarding the safety of ethylene oxide sterilization. This paper examines the effects of these radiation modalities on silicone rubber, and its applicability on a silicone rubber-containing medical device, specifically a silicone foley catheter, by assessing its functional properties before and after irradiation at varying absorbed doses.Analysis of the irradiated samples revealed the presence of carbonyl groups, indicating radiation-induced oxidation. Gamma irradiation did not exhibit fundamental changes in the polymer structure but showed degradation at higher temperatures due to oxidation mechanisms. Moreover, a significant decrease in elongation at break was observed indicating that the already highly crosslinked silicone rubber experienced additional crosslinking affecting its mechanical properties. In contrast, both irradiations led to degradation, as evidenced by a decrease in TG residue. However, the mechanical properties, including tensile strength and elongation at break, were less affected. This suggests limited crosslinking and fragmentation of the polymer backbone. At a lower dose, a decrease in both strength and elongation indicated the formation of branched structures, limiting mobility, introducing irregularities, and weakening the polymer's overall strength. Despite these effects, the functional properties of the silicone foley catheter were practically unaffected at low absorbed doses, except for the discoloration of the syringe ports. Overall, the study provides insights into the effects of ionizing radiation on silicone rubber, highlighting the complex interplay between crosslinking, chain scission, and oxidation mechanisms. The findings contribute to understanding the changes in the polymer's structure and properties under different radiation modalities and doses, facilitating the development of effective sterilization techniques for medical devices containing silicone rubber.

Reducing O2 sensitivity in electrochemical nitric oxide releasing catheters: An O2-tolerant copper(II)-ligand nitrite reduction catalyst and a glucose oxidase catheter coating

Electrocatalytic nitric oxide (NO) generation from nitrite (NO2–) within a single lumen of a dual-lumen catheter using CuII-ligand (CuII-L) mediators have been successful at demonstrating NO’s potent antimicrobial and antithrombotic properties to reduce bacterial counts and mitigate clotting under low oxygen conditions (e.g., venous blood). Under more aerobic conditions, the O2 sensitivity of the Cu(II)-ligand catalysts and the reaction of O2 (highly soluble in the catheter material) with the NO diffusing through the outer walls of the catheters results in a large decreases in NO fluxes from the surfaces of the catheters, reducing the utility of this approach. Herein, we describe a new more O2-tolerant CuII-L catalyst, [Cu(BEPA-EtSO3)(OTf)], as well as a potentially useful immobilized glucose oxidase enzyme-coating approach that greatly reduces the NO reactivity with oxygen as the NO partitions and diffuses through the catheter material. Results from this work demonstrate that very effective NO fluxes (>1*10−10 mol min−1 cm−2) from a single-lumen silicone rubber catheter can be achieved in the presence of up to 10% O2 saturated solutions.

Tough Hydrogel Coating on Silicone Rubber with Improved Antifouling and Antibacterial Properties

Silicone rubber catheters have a wide range of medical applications. However, silicone rubber is subject to biofouling, biofilm formation, and microbial infection, which can decrease its success and performance because of lipophilicity. In this report, a tough hydrogel was grafted onto the surface of silicone rubber to endow it with antifouling and antibacterial properties. First of all, an acrylamide (AAm)-, 2-methacryloxyethyl phosphorylcholine (MPC)-, and zinc methacrylate (ZMA)-derived poly(AAm-MPC-ZMA) hydrogel was coated on the surface of silicone rubber mediated by a poly(vinyl acetate) (PVAc) primer layer. Second, the composition and hydrophilicity of the hydrogel-coated rubber were evaluated by X-ray photoelectron spectroscopy (XPS) and a contact angle analyzer. The results indicated the success of the poly(AAm-MPC-ZMA) hydrogel coating, inducing a decrease in the contact angle from 107.01 to 23.22°. Bovine serum albumin (BSA) was further used to test the nonspecific protein absorption of the modified silicone rubber. It was found that BSA deposition on the surface of silicone rubber decreased from 0.33 to 0.07 mg/cm2 after coating, indicating an antifouling effect. In addition, the incorporation of ZMA gave silicone rubber significant antibacterial properties against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. As a preliminary application test, a silicone rubber catheter was coated with the poly(AAm-MPC-ZMA) hydrogel, which showed improved hydrophilicity and reduced adhesion against biological soft tissues. Taken together, the poly(AAm-MPC-ZMA) hydrogel coating generated a highly hydrophilic silicone rubber with excellent antifouling and antibacterial properties, which has great potential in the application of medical catheters.

Comparison of Copper(II)–Ligand Complexes as Mediators for Preparing Electrochemically Modulated Nitric Oxide-Releasing Catheters

Further studies aimed at examining the activity of different Cu(II)-ligand complexes to serve as electron-transfer mediators to prepare novel antimicrobial/thromboresistant nitric oxide (NO)-releasing intravenous catheters are reported. In these devices, the NO release can be modulated by applying different potentials or currents to reduce the Cu(II)-complexes to Cu(I) species which then reduce nitrite ions into NO(g) within a lumen of the catheter. Four different ligands are compared with respect to NO generation efficiency and stability over time using both single- and dual-lumen silicone rubber catheters: N-propanoate- N, N-bis(2-pyridylethyl)amine (BEPA-Pr), N-propanoate- N, N-bis(2-pyridylmethyl)amine (BMPA-Pr), 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN), and tris(2-pyridylmethyl)amine (TPMA). Of these, the Cu(II)BEPA-Pr and Cu(II)Me3TACN complexes provide biomedically useful NO fluxes from the surface of the catheters, >2 × 10-10 mol·min-1·cm-2, under conditions mimicking the bloodstream environment. Cu(II)Me3TACN exhibits the best stability over time with a steady and continuous NO release observed for 8 d under a nitrogen atmosphere. Antimicrobial experiments conducted over 5 d with NO-releasing catheters turned "on" electrochemically for only 3 or 6 h each day revealed >2 logarithmic units in reduction of bacterial biofilm attached to the catheter surfaces. The use of optimal Cu(II)-ligand complexes within a lumen reservoir along with high levels of nitrite ions can potentially provide an effective method of preventing/decreasing the rate of infections caused by intravascular catheters.

Improved hemocompatibility and analytical performance of intravascular oxygen sensors via nitric oxide (NO) releasing catheters

Event Abstract Back to Event Improved hemocompatibility and analytical performance of intravascular oxygen sensors via nitric oxide (NO) releasing catheters Elizabeth Brisbois1, Hang Ren2, Madeline Mccabe2, Terry C. Major1, Mark E. Meyerhoff2 and Robert H. Bartlett1 1 University of Michigan, Surgery, United States 2 University of Michigan, Chemistry, United States Introduction: Continuous monitoring of blood analytes (e.g., blood gases, pH, glucose, lactate, etc.) could provide valuable information needed for the diagnosis and treatment of patients. However, implantable biosensors and other blood-contacting devices suffer from two major clinical problems: clotting and infection. Thrombus formation on implantable sensors can severely impact their accuracy due to the metabolic activity of adhered cells altering the local levels of the analytes. One approach to improving hemocompatibility is the development of polymers that mimic the NO release from the normal endothelium (NO surface flux of 0.5-4x10-10 mol cm-2 min-1) that is a known potent inhibitor of platelet adhesion/activation and endogenous antimicrobial agent. One approach has been the development of NO releasing polymers by incorporation of NO donor molecules, such as S-nitrosothiols (RSNOs) [1]-[3]. However, many RSNO-based polymers have been limited by rapid leaching, low synthetic yields, and instability during storage. Recent work has shown that incorporating S-nitroso-N-acetylpenicillamine (SNAP) within hydrophobic polymers creates materials with long-term NO release and excellent storage stability [4]. In this study, a novel solvent swelling technique is used to load the walls of catheters with SNAP. The SNAP-based catheters are used to fabricate intravascular oxygen (PO2) sensors and their biocompatibility is evaluated in a rabbit model. Methods: The SNAP-based catheters were prepared by swelling silicone rubber catheters in a tetrahydrofuran solution containing SNAP. Control and SNAP-based catheters were used to fabricate the Clark-style amperometric PO2 sensors. The catheter lumen was filled with 0.15 M KCl in 0.1 M bicarbonate/carbonate buffer (pH 10). A Pt and a Ag/AgCl wire were inserted in the catheter lumen, and both ends of the catheter were sealed with silicone rubber. The PO2 sensors were soaked in 10 mM PBS, 100µM EDTA at 37 °C. NO release from the SNAP-based PO2 sensors under physiological conditions was determined via a chemiluminescence NO analyzer (Sievers280i, Boulder, CO). Sensors were calibrated by immersing in PBS and bubbling with O2 (0-100%). A potential of -0.7 V was applied to the Pt working electrode and the current was recorded. A rabbit model (sensors placed in veins) was used to evaluate the effects on thrombus formation and analytical PO2 sensing performance, as compared to a blood gas analyzer. After 7 h, the sensors were explanted, pictures were taken of the thrombus, and the 2D representation of the thrombus area was determined with the NIH ImageJ software. Results: The SNAP-based PO2 sensors can release NO under physiological conditions for up to 2 weeks (Fig. 1). During in vitro calibrations, the SNAP-based and control sensors had similar responses to various levels of oxygen in terms of sensitivity and response times (Fig. 2). Control (without NO release) and SNAP-based PO2 sensors were evaluated in a rabbit model. The SNAP-based PO2 sensors were found to accurately measure the PO2 levels in blood (within 10% of a standard benchtop blood gas analyzer). At the end of 7 h, the SNAP-based PO2 sensors were also found to have significantly reduced thrombus formation (as compared to controls). Conclusions: NO releasing catheters can be prepared with a novel solvent swelling technique that loads the walls of existing/commercial silicone rubber catheter tubing with SNAP. These SNAP-based catheters can be used to fabricate intravascular PO2 sensors with enhanced hemocompatibility properties and more accurate PO2 measurements. The NO release levels observed from the SNAP-based PO2 sensors are expected to also possess antimicrobial properties against bloodborne pathogens (e.g., S. aureus, S. epidermidis) [5],[6]. The SNAP solvent swelling technique also has the potential of improving the hemocompatibility of other blood-contacting devices (e.g., catheters, extracorporeal circuits, etc.). This work was supported in part by the University of Michigan Postdoctoral Translational Scholars Program (UL1TR000433) and NIH grant R01HL128337.

The preparation and characterization of nitric oxide releasing silicone rubber materials impregnated with S-nitroso-tert-dodecyl mercaptan.

Recently, considerable research efforts have focused on increasing the biocompatibility a nd bactericidal activity of biomedical polymeric devices (e.g., catheters, etc.) through incorporation of nitric oxide (NO) releasing molecules. NO is an important endogenous molecule that is well known for enhancing blood flow via its vasodilatory activity, but it also exhibits potent antithrombotic and antimicrobial properties. In this work, we demonstrate that silicone rubber tubing can be impregnated with a tertiary S-nitrosothiol (RSNO), S-nitroso-tert-dodecylmercaptan, via a simple solvent swelling method. We further characterize the NO release and RSNO leaching from the tubing over time via use of chemiluminescence and UV/Vis spectroscopy, respectively. The tubing is shown to maintain an NO flux above the physiological levels released by endothelial cells, 0.5-4.0 × 10-10 molcm-2min-1, for more than 3 weeks while stored at 37 °C and exhibit minimal leaching. Finally, the RSNO impregnated tu bing exhibits significant antimicrobial activity over a 21 d period (vs. controls) during incubation in a CDC bioreactor after inoculation of media with S. aureus bacteria. The use of such lipophilic RSNO impregnated silicone rubber tubing could dramatically reduce the risk of catheter-related infections, which are a common problem associated with placement of intravascular or urinary catheters.

Electrochemically Modulated Nitric Oxide (NO) Releasing Biomedical Devices via Copper(II)-Tri(2-pyridylmethyl)amine Mediated Reduction of Nitrite

A controllable and inexpensive electrochemical nitric oxide (NO) release system is demonstrated to improve hemocompatibility and reduce bacterial biofilm formation on biomedical devices. Nitric oxide is produced from the electrochemical reduction of nitrite using a copper(II)-tri(2-pyridylmethyl)amine (Cu(II)TPMA) complex as a mediator, and the temporal profile of NO release can be modulated readily by applying different cathodic potentials. Single lumen and dual lumen silicone rubber catheters are employed as initial model biomedical devices incorporating this novel NO release approach. The modified catheters can release a steady, physiologically-relevant flux of NO for more than 7 days. Both single and dual lumen catheters with continuous NO release exhibit greatly reduced thrombus formation on their surfaces after short-term 7-h intravascular placement in rabbit veins (p < 0.02, n = 6). Three day in vitro antimicrobial experiments, in which the catheters are “turned on” for only 3 h of NO release each day, exhibit more than a 100-fold decrease in the amount of surface attached live bacteria (n = 5). These results suggest that this electrochemical NO generation system could provide a robust and highly effective new approach to improving the thromboresistance and antimicrobial properties of intravascular catheters and potentially other biomedical devices.

The history of peritoneal dialysis: Early years at Toronto Western Hospital

The history of peritoneal dialysis: Early years at Toronto Western Hospital

(208) Arachnoiditis Associated with Intrathecal Analgesic Administration

Intrathecal analgesic administration via implanted drug infusion system has become a popular method of treating otherwise intractable pain. Drug reactions are known to occur but are typically similar to side effects that occur with systemic administration of the same drug and are reversible upon discontinuation of drug delivery. Symptoms consistent with arachnoiditis have been reported to occur with intrathecal infusion of high concentration bupivacaine but not for other agents, to our knowledge, and there are no reports describing arachnoiditis attributable to an indwelling intrathecal catheter. We treated a 47 year-old woman, with multiple drug allergies, who had complex regional pain syndrome II. She responded favorably to several single injections of intrathecal clonidine, had a successful trial with continuous intrathecal infusion of clonidine/morphine, and underwent implantation of a Medtronic 8617 pump and Model 8709 catheter. Approximately 2 weeks post-implant, she developed back and leg pain, numbness, and paresthesias throughout the distribution of the cauda equina. Evaluation revealed possible catheter migration into the subdural space. The catheter was revised and the daily dose of intrathecal clonidine/morphine was reduced with subsequent improvement of these symptoms. Several weeks later, she had the onset of progressively worsening back and leg pain and spasms (which became severe), cramping, numbness, and paresthesias in distribution of the cauda equina. Catheter studies, MRI, and CSF studies were normal. Drug infusion was discontinued with no improvement in symptoms. The infusion system was explanted due to concern about possible arachnoiditis induced by the silicone rubber catheter. We do not have proof of arachnoiditis in this case but the symptoms were classic for arachnoiditis, silicone rubber is known to produce an inflammatory reaction in some individuals, and we are not aware of any reports of arachnoiditis being associated with the infusion of either morphine or clonidine. There exists one other documented (not published) case in which a silicone rubber intrathecal catheter was felt to have induced arachnoiditis. This is a very rare occurrence but should be considered in the differential diagnosis of individuals with intrathecal infusion systems who develop symptoms of arachnoiditis.

History of Peritoneal Access Development

The first peritoneal accesses were devices that had been used in other fields (general surgery, urology, or gynecology): trocars, rubber catheters, and sump drains. In the period after World War II, numerous papers were published with various modifications of peritoneal dialysis. The majority of cases were treated with the continuous flow technique; rubber catheters for inflow and sump drains for outflow were commonly used. At the end of the 1940s, intermittent peritoneal dialysis started to be more frequently used. Severe complications of peritoneal accesses created incentive to design accesses specifically for peritoneal dialysis. The initial three, in the late 1940s, were modified sump drains; however, Ferris and Odel for the first time designed a soft, polyvinyl intraperitoneal tube with metal weights to keep the catheter tip in the pelvic gutter where the conditions for drain are the best. In the 1950s, intermittent peritoneal dialysis was established as the preferred technique; polyethylene and nylon catheters became commercially available and peritoneal dialysis was established as a valuable method for treatment of acute renal failure. The major breakthrough came in the 1960s. First of all, it was discovered that the silicone rubber was less irritating to the peritoneal membrane than other plastics. Then, it was found that polyester velour allowed an excellent tissue ingrowth creating a firm bond with the tissue. When a polyester cuff was glued to the catheter, it restricted catheter movement and created a closed tunnel between the integument and the peritoneal cavity. In 1968, Tenckhoff and Schechter combined these two features and designed a silicone rubber catheter with a polyester cuff for treatment of acute renal failure and two cuffs for treatment of chronic renal failure. This was the most important development in peritoneal access. Technological evolution never ends. Multiple attempts have been made to eliminate remaining complications of the Tenckhoff catheter such as exit/tunnel infection, external cuff extrusion, migration leading to obstruction, dialysate leaks, recurrent peritonitis, and infusion or pressure pain. New designs combined the best features of the previous ones or incorporated new elements. Not all attempts have been successful, but many have. To prevent catheter migration, Di Paolo and his colleagues applied the old idea of providing weights at the catheter tips to Tenckhoff catheters. In another modification, Twardowski and his collaborators created a permanent bend to the intra-tunnel portion of the silicone catheter to eliminate cuff extrusions. The Tenckhoff catheter continues to be widely used for chronic peritoneal dialysis, although its use is decreasing in favor of swan-neck catheters. Soft, silicone rubber instead of rigid tubing virtually eliminated such early complications as bowel perforation or massive bleeding. Other complications, such as obstruction, pericatheter leaks, and superficial cuff extrusions have been markedly reduced in recent years, particularly with the use of swan-neck catheters and insertion through the rectus muscle instead of the midline. However, these complications still occur, so new designs are being tried.

Reduced catheter sepsis and prolonged catheter life using a tunnelled silicone rubber catheter for total parenteral nutrition

One hundred and five patients were given total parenteral nutrition (TPN) for an average of 15 days via centrally placed venous catheters. Thirty-seven polyvinyl chloride (PVC) and 80 silicone rubber catheters were used. All the silicone rubber and 8 of the PVC catheters were buried in a subcutaneous tunnel. When silicone rubber catheters were used, there was significantly less catheter sepsis (P much less than 0.01), catheter life was prolonged by 50 per cent and fewer catheter insertions per patient were necessary.

Biofilm formation and changes in bacterial cell surface hydrophobicity during growth in a CAPD model system.

Peritonitis is a frequent complication of continuous ambulatory peritoneal dialysis (CAPD), with patients suffering recurrent attacks. The microorganisms most frequently implicated in the infection are the skin microflora, in particular, the coagulase-negative staphylococci such as Staphylococcus epidermidis. These microorganisms gain access to the peritoneal cavity via the in-dwelling silicone rubber catheter in the abdominal wall and often persist as biofilms on the surface of the catheter. The surface characteristics of S. epidermidis were monitored during growth in a CAPD in-vitro model together with their ability to adhere to silicone rubber substrata. Fresh dialysis fluid exerted an injurious effect on the cells leading to a decrease in cell numbers but during the simulated dialysis period the cells adapted to the applied stresses. Over a 96-h period in the model both a clinical isolate and a skin isolate of S. epidermidis adopted a more hydrophobic phenotype. The data presented here show that the bacteria grown in this in-vivo reflective CAPD model continually adapt to their environment and become more tolerant to the stresses imposed. The adapted cells were seen to colonise silicone rubber substrata.

Implantation of Permanent Jugular Catheters in Patients on Regular Dialysis Treatment: Ten Years’ Experience

Dual-lumen cuffed central venous catheter proved an important alternative vascular access compared to conventional arteriovenous (Cimino-Brescia) shunt in a selected group of patients on regular dialysis treatment. Typically, these catheters are used as bridging access, until fistula or graft is ready for use, or as permanent access when an arteriovenous fistula or graft is not planned (NKF-DOQI). We conducted a prospective study on IJV permanent catheter insertion and its related earlier and long-term complications. From February 1991 to February 2001 we inserted in 124 patients in end stage renal disease 135 cuffed catheters (130 in the right IJV and 5 in the left IJV), 92 of which were Permcath, 27 Vascath, and 16 Ash-Split. We performed the insertion of catheters by puncturing the IJV under ultrasonographic guid-ance in the lower side of the Sedillot triangle and checking the accurate position of the tip by endocavitary electrocardiography (EC-ECG). The duration of catheter use was from 60 to 1460 days, mean 345 days. The actuarial survival rate at 1 year was 82%, at 2 years 56%, at 3 years 42% and at 4 years 20%. The exit site infection and septicemia rates were 5.2 and 2.86 per 1000 catheter days respectively. Catheter sepsis was implicated in the death of three patients, all of whom had multiple medical problems. Several episodes of thrombosis (6% of dialyses) occurred which required urokinase treatment, and catheter replacement in 12 patients (9.6%). In 3 cases the catheters were displaced and correct repositioning was performed. Two catheters (Ash-Split) were replaced due to accidental damage of the external portion of catheters (alcoholic disinfectant). Catheter tip embolism occurred on one occasion during elective catheter exchange over guide-wire. One of the common problems encountered with cuffed tunneled catheters is poor blood flow, most often secondary to the formation of a fibrin sheath around the lumen. Even if we conducted a non-randomized study, in our experience, the higher rate of malfunctioning catheters was in the group with no anticoagulation therapy. Therefore, we suggest anticoagulation treatment in all patients wearing central vascular catheters with no contraindication. Just one year ago, we followed NKF-DOQI clinical practice guidelines for vascular access that indicated that for patients who have a primary AV fistula maturing, but need im-mediate hemodialysis, tunneled cuffed catheters are the access of choice and the preferred insertion site is the right IJV. Considering recent reports of permanent central venous stenosis or occlusion after IJV can-nulation, currently, our first choice is femoral vein cannulation with smooth silicone rubber catheters, tunneled if long-term utilization is needed (more the 3-4 weeks). In our opinion, the right IJV puncture is to be avoided as much as the venipuncture of arm veins suitable for vascular access placement, particularly the cephalic vein of the non-dominant arm. Our data confirm that permanent venous catheters might rep-resent an effective long-term vascular access for chronic hemodialysis, particularly for older patients with cardiovascular disease and for cancer patients.

FUNCTIONAL ANATOMY OF THE MALE FELINE URETHRA: MORPHOLOGICAL AND PHYSIOLOGICAL CORRELATIONS

Anatomical and histological methods were combined with measurements of the urethral pressure profile (UPP) to investigate the functional aspects of the urethra in male cats. A silicone rubber catheter with two microdiaphragm pressure transducers was used to measure the UPP. Gross anatomy and ultrastructure of the urethra at each segment were examined and correlated with the pressure profile data. The preprostatic urethra was composed of three layers of smooth muscle, while distal to the prostate striated muscle became predominant. Increased baseline pressure and rapid fluctuations in pressure in the postprostatic urethra and bulbourethra resulted from the function of periurethral striated musculature. The UPP was affected by the bladder pressure, repetition of the measurement, the sensor orientation in the urethra, and the type of measurement catheter. Well controlled high fidelity measurements enabled a clear correlation to be established between the features of the UPP and the anatomy of the urethra and surrounding musculature. Additionally, observations on the ultrastructural and microscopic anatomy of the urethra extend a previous description of the pelvic urethra.

Gastrostomy button conversion into a combined gastric and jejunal access device

Purpose : The aim of this report is to describe the conversion of a gastrostomy button into a combined gastric decompression and jejunal feeding device. Methods : In this technique two 9.6F single-lumen central venous silicone rubber catheters are threaded through the shaft of a 24F gastrostomy button. The longer limb is guided into the jejunum, and the shorter one rests in the stomach. The remaining space in the shaft is filled with silicone rubber paste. Results : The approach was successfully used in seven neurologically impaired children. Conclusion : This arrangement provides effective palliative gastric and jejunal access.

Repair of Chronic Peritoneal Dialysis Catheter

Damage to the peritoneal dialysis catheter may be due to wear from long-term use, exposure to antibacterial agents (strong oxidants), and accidental injury from sharp objects. Repair of such catheter, if not associated with subsequent complications, would extend catheter life and reduce costs and patient inconvenience related to catheter replacement. Retrospective analysis of seven peritoneal catheters repaired 11 times over a 15-year period by splicing the old catheter with an extension tube using the Peri-Patch Repair Kit (Quinton Instrument Co., Bothwell, WA, U.S.A.). The life of these seven catheters was extended by a mean of 26 months (range 1-87 months), without increasing infection rates after splicing. The peritonitis rate after catheter splicing was 0.40 per year, not higher than the overall rate (0.76 per year) in our center during the same time period. Exit-site infections occurred in 6 patients after catheter splicing. Only one infection was related to trauma during the procedure and resulted in chronic exit infection; the catheter was eventually removed. In this patient, damage to the catheter was less than 1.5 cm from the exit site. Splicing of the damaged peritoneal catheter, if properly done, is a safe procedure and can significantly prolong catheter life. We recommend that measures to prevent catheter damage, such as avoiding the use of scissors and other sharp objects, should be emphasized during the initial patient education and training. Alcohol and iodine should not be used on silicone rubber catheters. We suggest that the patient should report catheter damage immediately and come to the clinic within a few hours for catheter splicing (if possible) and prophylactic antibiotic to prevent peritonitis. Finally, we recommend that repair of the catheter should not be attempted if the breakage is less than 2 cm from the exit site, unless done as an emergency procedure if immediate catheter replacement cannot be performed.

Mechanical dysfunction of ventriculoperitoneal shunts caused by calcification of the silicone rubber catheter.

The authors studied new and calcified shunt catheters to identify the prevalence of failures caused by aging materials in the shunt. Complications associated with these devices have various origins. Among late complications, fracture or migration of the system is related to the subcutaneous adhesion of the distal tubing in a growing child. A review of a cohort of 64 children who underwent shunt placement in 1980 with barium-impregnated distal catheters showed that 10 of these patients underwent reoperation for complications related to aging of the shunt material. This group represents 15% of the whole series and 30% of those children who were followed for more than 3 years. The true impact of aging of materials on shunt function is probably underestimated. The authors performed physical, chemical, and mechanical analyses of the retrieved aged catheters and also of new catheters, resulting in the following findings: 1) calcifications were observed only on the external surface of the catheter, predominantly in its subcutaneous segment at the level of the neck and anterior chest wall; 2) calcifications contained particles of free silicon and barium sulfate, signifying fragmentation of the polymer; 3) the microstructure of the silicone polymer was modified: microfractures and alteration of the polymeric network were observed; 4) silanol groups were observed on the external surface of the catheter; and 5) the mechanical properties of the silicone rubber were degraded, and the aged catheters were more brittle than the new ones, with ruptures at elongations and fracture energy much lower than that seen in new catheters. Furthermore, in vitro testing with a metastable solution of simulated body fluid demonstrated the critical impact of pH variations in liquid media and surface degradation of the catheters on the precipitation of hydroxylapatite crystals. Although most shunt complications can be addressed by better patient management and surgical technique, late complications appear to be partly related to aging of the material. Distal tubing calcifications have been observed in barium-impregnated catheters. The industry recently responded to these observations by introducing plain silicone-coated shunt tubing; further evaluation will show what improvement can be expected.

Recovery and biological activity of filgrastim after injection through silicone rubber catheters.

The recovery and biological activity of filgrastim after injection through a silicone rubber catheter were studied. Various volumes of filgrastim injection 300 micrograms/mL (0.17, 0.34, 0.51, 0.68, 0.85, and 1.0 mL) were injected through silicone rubber catheters and collected in glass vials to simulate intravenous bolus injections. The catheters were flushed with 3 mL of 5% dextrose injection before and after the injections. For some catheters, the procedure was repeated to simulate the administration of a second filgrastim dose through the same catheter. The theoretical filgrastim concentration in the expelled fluid was 16.1, 30.5, 43.6, 55.4, 66.2, or 75.0 micrograms/mL (corresponding to the filgrastim injection volumes). Filgrastim concentrations in expelled fluid were measured with an enzyme-linked immunosorbent assay, and biological activity was measured with a mitogenic cell-culture assay. There was > or = 10% loss of filgrastim after the first injection when the injection volume was 0.17, 0.34, or 0.68 mL. Mean drug recovery after the second filgrastim injection exceeded that after the first for all six volumes and was > or = 90% for five volumes. The recovered filgrastim retained all of its activity. A > or = 10% loss of filgrastim occurred for three of six volumes after one injection through a silicon rubber catheter. Recovery was higher after a second injection through the same catheter. Biological activity was not affected.

Double Catheterization of the Internal Jugular Vein for Hemodialysis: Indications, Techniques, and Clinical Results

Central vascular catheters are used to access the central vascular system in both acute and chronic uremic patients undergoing hemodialysis. Among different approaches, the internal jugular vein seems to have less adverse effects. We describe our long-term experience with a two-catheter system. Percutaneous jugular vein cannulation was performed using Medcomp silicone rubber catheters. The study included 108 patients undergoing hemodialysis. One- and 2-year survival was 93 and 91%, respectively; 36 died because of unrelated causes. Blood flow rate was 284 mL/min; venous pressure at 1 year was 90 mm Hg. Complications included accidental withdrawal (6), dysfunction (4), catheter clotting (11), mediastinal hematoma (2), pneumothorax (1), and sepsis (7). Good long-term survival and a low complication rate make this system a safe and reliable method of access for long-term hemodialysis.