A mechatronic haemodialysis system for the treatment of acute renal failure and metabolic disorders

The aim of this project was to produce a fully automated prototype system for the treatment of premature babies who are suffering from renal failure or metabolic disorders. These patients are difficult or impossible to treat conventionally, due to their very small total blood volume and their intolerance to donated blood. There was a strong case for developing a dialysis system specifically designed for the treatment of such patients. The system is based on a manually operated device developed at the Royal Victoria Infirmary, Newcastle Upon Tyne. It differs from conventional dialysis methods in several ways. Blood access to the patient is via a single venous catheter. Only a very small amount of blood is needed to prime the extracorporeal circuit - this can be as little as 6.8 ml in the smallest patients. This compares very favourably with the volumes needed in conventional circuits, which are in the range of 15 - 40 ml. This small priming volume means that donated blood is not needed to prime the circuit. The clearance and ultrafiltration rates that can be achieved are independent of the rate that blood can be accessed from the patient, since the same blood passes back and forth through the haemofilter several times. The clearances that have been obtained experimentally are consistently above 40% of the mean blood flow rate through the system. The largest mean blood flow rate available is 5 ml/min, so the maximum clearance is approximately 2 ml/min. The maximum ultrafiltration rate that can be obtained is 50 ml/h. The new system is more effective at treating premature babies than conventional dialysis circuits. The hand driven system was tested in vivo and found to work well, so the automated system was developed on a solid foundation. A prototype system has been successfully developed and tested. This thesis details both the development and the testing. The new system uses stepper motors and DC servo motors for actuation, and is controlled by Labwindows/CVI and NIDAQ software running on a standard PC platform. The interface between the PC and the machine is provided by a National Instruments data acquisition board. A comprehensive single fault analysis of the safety of the system was undertaken, including both software and hardware. In vitro testing covered several areas of operation. The accuracy of the ultrafiltration process was established. The clearance rates that could be achieved were determined. The amount of damage caused to the blood by the system was also tested. This was found to be well within acceptable clinical limits. In vivo testing established the feasibility of using a computer algorithm to control the withdrawal of blood from the patient. Finally, the system was successfully used to treat a patient with an in-born metabolic disorder. In summary, a new system has been developed that is superior to any other treatment method currently available for neonates with these types of disorders.