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Epidural infections are a rare but serious complication which can result in an irreversible neurological damage if not treated. Catheterization of the epidural space is routinely used in anesthesia and analgesia, which connects the epidural space with the outside environment, through which bacteria can gain access to the epidural space.1–3 Here, the use of epidural filter serves as a physical barrier to prevent ingress of bacteria through the infusion line. In this study, we investigated the survivability of seven typical pathogens in bupivacaine and ropivacaine when contaminated during manipulation (eg, local anesthesia (LA) bolus application/infusion) and the ability of an epidural flat filter to prevent microbial transmission by a contaminated infusion solution until physical occlusion of the filter.
The survivability of seven typical device-associated pathogens was tested by artificial microbial contamination (1.25×105 colony-forming units (CFU)/mL) of different concentrations of two commonly used epidural anesthetics, bupivacaine and ropivacaine. The number of vital micro-organisms was checked daily over a period of 4 days by plating out aliquots and CFU counting.
The maintenance of the microbial barrier function of a 0.2 µm epidural catheter filter (Perifix from B. Braun) was investigated by the presence of microbial contamination in the flow-through solution after challenging the filter with an artificially contaminated infusion solution with test bacteria Staphylococcus aureus or Pseudomonas aeruginosa by a volumetric infusion pump at a speed of 10 mL/hour until automated pressure shutdown was observed due to physical/mechanical occlusion of the filter by bacteria.
Microbial survivability in anesthetics bupivacaine and ropivacaine
The number of vital organisms in the anesthetics bupivacaine and ropivacaine was reduced over time. However, some pathogens (S. aureus, P. aeruginosa and Candida albicans) were able to survive to a certain degree over the test period of 4 days (figure 1).
Microbial tightness of epidural filter
For physical occlusion of a 0.2 µm epidural flat filter by micro-organisms, a relatively high number of bacteria (≥5.5×108 CFUs) were required for both tested micro-organisms, S. epidermidis and P. aeruginosa, respectively. The filter maintained its microbial barrier function even after physical occlusion as no bacteria were detectable in the flow-through fraction (figure 2). The level of vital bacteria remained comparable throughout the test.
This in vitro study demonstrated that different typical device-associated pathogens can survive over a period of several days directly in the anesthetic solutions bupivacaine and ropivacaine. Furthermore, it was shown that an 0.2 µm epidural flat filter can efficiently prevent microbial transmission even when challenged with high numbers of bacteria until physical occlusion and pressure shutdown was achieved.
It was shown that ropivacaine exhibited poor antibacterial activities,4–6 whereas bupivacaine showed concentration-dependent antibacterial activity.4 While other studies investigated on antibacterial activity in the presence of growth medium, our study focused on the ability to survive directly in the anesthetic solution simulating microbial contamination during drug admixture.
Maintaining filter integrity and microbial tightness even when physical occlusion by microorganism is achieved has not been reported so far. Interestingly, the number of micro-organisms leading to physical occlusion of the epidural filter was observed with a very high concentration of bacteria (>108 CFU).
Noteworthy, the contamination level chosen in this study was higher than that in a normal clinical environment in order to determine the required bioburden to obtain physical occlusion of the epidural filter. The results of our investigation demonstrate that microbial barrier function was even sustained when physical occlusion of the peridural flat filter by >108 bacteria was attained. Thus, the duration time of epidural flat filters is not limited by time but mainly by the flow rate, which is influenced by the number of germs, particles and air which can block the membrane mechanically. Thus, the recommendation is to keep the system closed as long as technically possible (closed system). However, this study investigated selected aspects of the epidural filter in an in vitro setup and, thus, the behavior in an in vivo clinical environment could be different and has to be further investigated in clinical settings.
Contributors JB and TR designed the experiments. JB performed the experiments and took the lead in writing the manuscript. NK and PK contributed to the interpretation of the results. All authors provided critical feedback and helped shape the research, analysis and manuscript.
Funding This study was funded by B. Braun Melsungen AG, Melsungen, Germany.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.