A microbiological survey of bicarbonate-based replacement circuits in continuous veno-venous hemofiltration*

Abstract

OBJECTIVE: The potential for clinically significant transfer of pyrogen-inducing material in dialysate and substitution fluids is well recognized in the setting of chronic hemodialysis and hemodiafiltration and has led to the establishment of strict standards for microbiological purity. Preliminary evidence has indicated the potential for fluid contamination in continuous renal replacement therapy, and although the scale of the problem in contemporary, industry-standard equipment is unclear. We aimed to define the microbial integrity of modern continuous veno-venous hemofiltration (CVVH) replacement fluid circuitry. DESIGN: Twenty-four CVVH replacement fluid circuits (mean lifespan, 34.2 hours; range, 4-86) were studied at completion of therapy. SETTING: The integrated critical care unit and cardiothoracic intensive care unit of the Freeman Hospital, Newcastle upon Tyne, United Kingdom, between January and August 2007. SUBJECTS: Patients with renal failure receiving treatment with CVVH. INTERVENTIONS: Nil. MEASUREMENTS: Culture and endotoxin assays of replacement fluid, culture of endoluminal swabs, and electron microscopy of harvested tubing. MAIN RESULTS: Of the 24 replacement fluid cultures, nine (mean lifespan 32.8 hours, range 5-79) breached European Pharmacopoeia standards for ultrapure water (<0.1 colony-forming units/mL). One of 24 endotoxin measurements breached European Pharmacopoeia standards (<0.03 endotoxin units/mL). Internal tubing cultures were negative, but electron microscopy revealed 13 of the 24 collected tubing samples to be contaminated with biofilm. Only seven of the 24 studied circuits proved to be free from microbial contamination. CONCLUSIONS: We have confirmed frequent breaches of microbial integrity in industry-standard, bicarbonate-based CVVH, indicating the potential for added risk to the vulnerable, critically ill patient. These findings are of particular concern given the need for systemic infusion of replacement fluid. Measures to reduce the levels of contamination and their impact are discussed.