Bacterial contamination of dialysate in dialysis-associated endotoxaemia

Bacteriological investigations and endotoxin (ET) determinations were performed during a routine haemodialysis session for six patients. The glucose free dialysate was prepared with untreated tap water. All patients were dialysed for 5 h. Pseudomonas aeruginosa was regularly isolated in numbers up to 10(7) cfu ml-1 from samples of the dialysate inflow, the dialysate site and the dialysate outflow. ET levels in the plasma of the patients increased continuously during haemodialysis and were always higher in the blood outflow line of the dialyzer than in the blood inflow. Despite the high bacterial counts in the dialysate and the increasing ET levels in the patients plasma neither bacteraemia nor fever was observed. The former is due to the impermeability of the dialyzer membrane for bacteria, the latter is explained by low pyrogenicity of P. aeruginosa endotoxin. Inspection of the dialyzer machines revealed that air-traps and heater-unit for the incoming (untreated) tap water before mixing with the dialysate concentrate were the only sites where high bacterial release was feasible, as this part of the machine escaped disinfection due to the construction of these devices. We recommend the regular disinfection of all parts of a dialyzer machine, including heating units, air traps and valves.