Microbiological and scanning electron microscopic evaluation of epidural catheters

Abstract

Background: Epidural catheters are frequently colonized by gram-positive bacteria. Although the incidence of associated epidural infections is low, their consequences can be devastating. We investigated bacterial growth on epidural catheters by quantitative bacterial culture and scanning electron microscopy (SEM) in order to explore the patterns of epidural catheter colonization.

Methods: 28 patients undergoing major abdominal surgery with thoracic epidurals (treatment ≥72 hours) were studied. Before the removal of the catheter, the skin surrounding the insertion site was swabbed. The entire catheter was divided into extracorporeal, subcutaneous, and tip segments. Skin swabs and catheter segments were quantitatively cultured, bacterial species were identified, and SEM was performed on four selected catheters.

Results: 27 of 28 catheters were included. The percentages of positive cultures were: skin swab 29.6%, extracorporeal segments 11.1%, subcutaneous segments 14.8%, and tip segments 33.3%. One patient was diagnosed with a catheter-associated infection. Staphylococcus epidermidis was cultured from the skin and the catheter extracorporeal, subcutaneous, and tip segments. SEM of this catheter showed bacteria-like and intraluminal host cell-like structures. SEM of two other catheters showed intraluminal fibrin networks in their tip segments.

Conclusions: We present the first SEM pictures of an epidural catheter with a bacterial infection. Bacterial growth developed from the skin to the tip of this catheter, indicating the skin as a primary source of infection. By SEM, catheters with low levels of bacterial growth demonstrated an intraluminal fibrous network which possibly plays a role in catheter obstruction.

Keywords: neuraxial blocks: continuous techniques; neuraxial blocks: epidural; regional anesthesia.

Figure 1

Schematic overview of epidural catheter segments and skin swab used for quantitative bacterial culture (blue segments) or scanning electron microscopy (orange segments). EC1 is the extracorporeal segment; SkSw1 is skin swab; SC1, SC2, SC3 are subcutaneous segments, from superficial (SC1) to deep (SC3); T1, T2, T3 are tip segments (T3 is the end of the epidural catheter).

Figure 2

Scanning electron microscope images of the sterile epidural catheter, not inserted in the patient. (A) Outer surface of the catheter with a side hole. (B) Outer surface of the tip. (C) Cross-section of the catheter showing the catheter wall and lumen. White bar indicates scale.

Figure 3

Scanning electron microscope images of subcutaneous segments of infected epidural catheter (patient 5). Outer surface of the catheter with (A) low, (B) medium, or (C) high magnification. The surface of the catheter is partially covered with biological deposits with staphylococci-like spheres, indicated by red arrows. Side view of the catheter lumen with adherent cell-like structures in (D) low and (E) medium magnification. Pseudopodia are emerging from the cell-like structures. White bar indicates scale.

Figure 4

Scanning electron microscope images of tip segments of the epidural catheter with low levels of bacterial growth (patient 29). (A) Outer surface of the catheter with biological deposits. (B) Cross-section of the catheter segment showing intraluminal fibrin-like fibers stretching in the length of the catheter. (C) Cross-section of the catheter with a side hole showing the intraluminal fibrous network and clot. Fibers seem to progress from the side hole to the intraluminal space. (D) Higher magnification of the side hole, showing an organized layer of cell-like structures lining the border and interior of the side hole. (E) Higher magnification of fibrin-like fibers with erythrocytes and blebs embedded in the fibrous network, indicated by white and red arrows, respectively. Black bars indicate scale.