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Management of chronic peritoneal ascites by transfer of the fluid to the right atrium via peritoneovenous shunt (PVS) is often complicated by occlusion of the peritoneal catheter by one, or a combination, of the following: 1) omental plugging of drain holes, 2) fibrin obstruction of the lumen, and 3) encapsulation of the peritoneal segment by a cocoon. A PVS design that includes an access port facilitates the reversal of fibrin obstruction by urokinase. Eight dogs with implanted PVS were tested weekly for patency (indicated by the flow rate of saline into the peritoneum via the access port) and performance (indicated by the percent transfer of saline from the peritoneum to the vasculature). In 256 test sessions performed to date, 15 catheter occlusions occurred. Nine of these were reversed by one or two flushes with 5,000 units of urokinase via the access port. The remaining six were found to be occluded by cocoons (two), omentum (three), and fibrin (one). Although it is an effective treatment for ascites, the PVS is not in common use, because it has a relatively high occlusion rate. The access port and other features of the authors' PVS are designed to reduce the incidence of PVS occlusion.

Now that implantable drug infusion pumps are well established clinically, methods for diagnosing suspected pump failures are needed. The authors previously constructed a benchtop data acquisition and control apparatus to assist our work in developing new pump technology. Although this device is technically capable of in vivo pump monitoring, it is cumbersome. Thus, they recently created a portable interrogation unit with more limited features. This portable pump interrogation apparatus consists of a 32 bit MS-DOS labtop computer, data acquisition software, an analog/ASCII interface, a pressure transducer, and appropriate fluid conduits. Communication between the device and the implanted pump is via a percutaneous needle puncture of the drug reservoir refill septum. This procedure is identical to that employed in a standard pump refill. Pump performance is evaluated by incrementally filling the pump reservoir while simultaneously measuring reservoir pressure. The resulting data are presented on the computer screen as a plot of pressure versus volume that quickly and simply either eliminates or confirms the reservoir pressure source as a failure mode. Diagnostic runs are saved on file for archival purposes. Their benchtop apparatus has been a valuable and reliable tool over many years of use. The authors believe that their portable apparatus will be equally beneficial.

In the current era of cost containment in medicine, manufacturing economics have become increasingly important. The authors devised an implantable pump powered by spring force from an elastomeric Belleville washer, which is also the outer flexible wall of the drug reservoir. Use of formed and injection molded parts provides for low-cost manufacturing, in contrast to the precision welded alternative designs. Additional advantages include insensitivity to changes in ambient temperature and pressure. Finite element modeling of the elastomer spring allows prediction of the effects of parameter changes on performance, so that expansions and reductions of scale can be made without compromising the uniform spring rate of the device. A concern that subcutaneous fibrous encapsulation might markedly alter reservoir pressure was not supported by experimental data. In a unit implanted subcutaneously in a dog, reservoir pressures measured over a 4 year period were stable. This new, simple, implantable infusion pump can serve as an economical vehicle for prolonged parenteral drug treatment of ambulatory subjects in circumstances where continuous single-rate infusion is appropriate.

An orthopedic catheter for long-term access to the synovial joint is anchored by a hollow threaded tap that penetrates the capsule through a hole drilled in the surrounding bone. The proximal end of the catheter is connected to either an implantable drug infusion pump or an implantable access port for continuous or intermittent perfusion or sampling. Four catheters were evaluated in dogs. Three were attached to ports, the fourth to a pump. Water (one trial, 22 weeks) and hyaluronic acid (HA) (5 mg/ml; two trials of 8 weeks each) were administered through ports twice weekly in 1.5 ml boluses; 5 mg/ml HA was delivered by pump (1 trial of 33 weeks) at 0.31 ml/day.

Long-term intravascular catheterization carries a finite risk of catheter occlusion. A catheter tip valve design is presented (Buchwald-Wigness, Strato Medical Corporation, Beverly, MA) which incorporates features designed to decrease the risk of thromboembolism and reduce the need for maintenance procedures. Aspiration and infusion are controlled by separate valves, making it possible to engineer optimized inlet and outlet parameters. The outlet valve is an elastic sleeve expanded around the sidewall outlet ports which opens under injection pressure. The inlet valve is a tubular elastic element compressed against the inlet port from within the lumen, opening under aspiration pressure. A series of valves were prototyped with outlet pressures ranging from 2 to 100" H2O, and inlet pressures ranging from -40-70" H2O, and flowrates at 36" H2O of greater than 1,400 ml/hr. Dog implants of two prototypes with outlet valve pressures of 10" H2O, and inlet pressures of -40" H2O, demonstrated that dormant periods of up to 7.5 weeks could be achieved without detectable blood cell entry into the lumen. No significant hemolysis was observed in blood samples aspirated with a 6 cc syringe (8% scored "slightly hemolyzed" vs. 44% with the nonvalved controls) indicating that a hemodialysis application is likely.

Buchwald, Henry; Guzman, Eugenio; Wigness, Bruce D.; Dorman, Frank D.; Rohde, Thomas D. Author Information

An implantable infusion pump which uses elastomer spring pressure to provide constant-rate drug delivery is described. Desirable features of the design are its low-cost construction, temperature and pressure insensitivity, high volumetric efficiency, and scale flexibility. Test results for prototype models are reported. Spring performance characteristics appear to be unaffected by long-term implantation. The results indicate that the pump is suitable for multiple-drug-delivery applications requiring more than an infusion port but needing a programmable device

Of the reasons to discontinue continuous implantable insulin pump therapy, flow rate reduction is the most common, occurring in 27 of 42 pumps in the University of Minnesota series. Thrombosis at the catheter tip appears to be a major reason for flow reduction. Six different procedures to restore flow in pumps were performed. Two of the procedures involve the infusion of an alkaline solution through the device, replacing the insulin/glycerol solution normally infused; the other four procedures are surgical ones involving manipulation of the catheter. In restoring flow the non-operative procedures achieved a success rate of 50%, having taken as long as 3 months to restore flow, and having allowed up to 1 year of further insulin pump therapy; flow in all the pumps so treated eventually decreased again. The operative procedures were nearly 100% successful, restored flow immediately, and allowed longer periods of adequate flow, but flow rate did again decrease. When flow rate reduction occurs further flow improvement procedures may be attempted without difficulty and are well tolerated. In implantable pumps the biocompatibility of the blood-catheter tip interface needs to be improved to deal with the recurrent problems of insulin infusion device flow rate decrease.

From August 1984 to December 1987, 10 patients received the Minnesota peritoneovenous shunt at our institution. Four of these patients previously had received seven Denver catheters with clinical and/or radiologic evidence of malfunction. Eight patients had the diagnosis of benign intractable ascites and two malignant ascites. In two hypercoagulable patients re-exploration of the intravascular limbs was necessary for fibrin plugging, but in no case have we seen catheter tip blood clot thrombosis. One shunt failed to work properly because of adhesions. At present, six of these patients are alive with a functioning shunt and four have died of nonshunt-related complications. The longest period of continuous function with a Minnesota shunt was 100 weeks. Data from this trial are compared retrospectively with data from patients who received LeVeen (n = 8) or Denver shunts (n = 7) at the University of Minnesota Hospitals during the same time period. Performance of the Minnesota shunt was comparable to the commercially available LeVeen and Denver shunts in most respects and appeared to offer advantages in longer functional life and reduction of intensive care unit admissions.

For today's most common peritoneovenous shunt catheters, the high incidence of complications (disseminated intravascular coagulation [DIC], pulmonary problems, clotting of the intravascular end, and shunt kinking) results in limited use. We have designed a new peritoneovenous shunt catheter in which we improved mechanical biocompatibility with respect to both the peritoneum and the vasculature. The device consists of: a multimicroorifice ascites filter in a double-chambered collecting device, a tubular compression pump with an intratubular check-valve, and a check-valve catheter at the intravascular end for positive exclusion of blood by reflux or back diffusion. This configuration filters the proteinaceous material from the ascites fluid, transports the filtrate into the blood stream, maintains patency, act to prevent DIC by inhibiting the creation and transport of microthrombi into the cardiovascular system, and eliminates clot formation at the intravascular end.

KERNSHNE, KEMP H.; KRYJESKI, SHEILA R.; WIGNESS, BRUCE D.; GOLDENBERG, FZY J.; ROHDE, THOMAS D.; DORMAN, FRANK D.; CHUTE, EDMUND P.; RUPP, WILLIAM M.; BUCHWALD, HENRY Author Information