Bacterial Contamination of Dialysing Fluid of Artificial Kidney.

During haemodialysis with the Kolff twin-coil artificial kidney the patient's blood is passed through " cellophane " tubing which is immersed in a dialysing bath. This holds 100 litres of fluid, with an electrolytic composition similar to that of the normal plasma, with an addition of 0.88% glucose. During haemodialysis, urea and other nitrogenous substances appear in increasing quantities. The bath is kept at a constant temperature of 370 C. and it was formerly our practice to change the dialysing fluid every three hours. (In the light of experience, however, we now change the bath at much shorter intervals.) In our early endeavours with this equipment we were disturbed to note an increasing turbidity of the fluid in the bath as dialysis progressed. Knowing that the contents of the dialysing bath constituted an ideal culture medium for some bacterial species, we suspected that the turbidity might be the result of bacterial growth. This led us to make a bacteriological investigation of the contents of the bath. The result of this we are now presenting. The equipment had been in clinical use for approximately two years at the time this inquiry was instituted, and it was customary to subject the equipment only to routine cleaning with soap, detergents, or mild abrasives. Bacterial Contamination of Dialysing Fluid Methods During dialysis 1-ml. samples of the dialysing fluid were examined bacteriologically by means of a viable count using a technique similar to that described by Miles et al. (1938). After incubation at 370 C. for 24 hours at least three drops of a suitable dilution on nutrient agar were used to calculate the number of organisms. Moistened swabs were employed to examine various parts of the dialysing bath and reservoir tank in which the second and third changes of solution were prepared. These swabs were taken after the tank had been cleaned and were plated on nutrient agar and incubated at 370 C. for 24 hours. Results A typical result of the viable counts during a dialysis is shown in Fig. 1. The total count plotted against the time of sampling showed two precipitous falls corresponding to the times when the bath fluid was changed. During the changing of the bath the whole contents cannot be removed by the pump, so that each new bath is necessarily inoculated from its predecessor. Since there were 60,000 organisms per ml. in the first bath of a …