Providing postoperative analgesia using epidural catheters has become increasingly popular now that the benefits of this procedure have been demonstrated in numerous settings. Perhaps the most significant concern of the provider is the potential for the development of an epidural space infection. The consequences of this complication can be severe and include paresis or outright paralysis if the diagnosis is delayed. In patients in whom epidural space infection is suspected, it is routine to pull the epidural catheter and to culture the tip of the epidural catheter to determine what organism may be responsible for the epidural space infection. The authors of this study set out to evaluate the clinical relevance of routine microbiological culture of a epidural catheter tip after use in acute pain management and to identify patterns of a culture result with respect to both indication for and duration of epidural catheterization.

The Acute Pain Service in this study was involved in the care of all of its patients at least once daily and kept detailed records on each patient. The APS protocol required epidural catheter tips to be sent for microbiological culture on removal. This data was collected over a four-year period. During this time, the APS saw 1,810 patients who had received epidural analgesia. The records of these patients were reviewed.

Culture results were available for 1,443 (79.7%) patients: 1,027 catheter tips (71.2%) were sterile, while 416 (28.8%) were positive for at least one type of microorganism. Clinically, no epidural space infections were identified. The highest positive culture rates were found from epidural catheters used in the treatment of pain from fracture ribs or fractured pelvis, while the lowest incidences occurred in elective orthopedic and thoracic surgery. The proportion of epidural catheters with positive culture results steadily increased with the duration of catheterization, but there were no clinically significant differences for catheters left in situ for either three or four days. The most frequently cultured organism was Coagulase negative staphylococcus. Gram negative organisms including Pseudomonas aeruginosa, Escherichia coli, Klebsiella and Proteus species were frequently identified often in the same culture. Other gram positive organisms including Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Enterococci were isolated less frequently.

The authors concluded that a significant proportion of epidural catheter tips may be "culture positive" after removal. It is suggested that this probably represents colonization of the skin at the catheter insertion site and subsequent contamination of the catheter tip on removal of the catheter. The large number of "culture positive" tips in the absence of clinically identifiable epidural space infection suggests that routine culture of epidural catheter tips is clinically irrelevant in the vast majority of cases, and that it is not a good predictor of the presence of an epidural space infection.

These authors have reviewed data and actions based on conventional wisdom with respect to determining potential organisms causing epidural space infection. Their conclusion flies in the face of conventional wisdom and suggests that routine culture of epidural catheter tips is clinically irrelevant in the vast majority of cases. It is not a good predictor of the presence of an epidural space infection and routine culture of epidural tips is no longer performed at their institution. Early detection of epidural space infection relies on constant monitoring for clinical symptoms and signs suggestive of an epidural abscess. The results of this study raise into question the need or the value of performing epidural catheter tip culture at all. If the results are positive in so many patients with no evidence for epidural space infection, it is hard to imagine that a positive culture in the presence of a presumed epidural space infection would provide any significant benefit. It is good to review practices that are taken as dogma to evaluate whether or not there is real value in continuing the current practice. If not, then other means may need to be considered in order to provide state-of-the-art care to our patients and to avoid complications which carry dire consequences.