Exploration of the patterns of microbial colonization of intravascular devices in severely ill patients

Innovations in healthcare have led to survival of a higher proportion of critically-ill, elderly and immuno-compromised patients. Intravascular devices (IVDs) are indispensable in providing safe, reliable vascular access and continuous haemodynamic monitoring of these patients in the intensive care unit. Unfortunately, many healthcare-acquired or nosocomial infections in severely ill patients can be caused by the very medical devices that are implanted to provide life-sustaining care. IVDs comprising peripheral arterial catheters (ACs), non-tunnelled short-term central venous catheters (CVCs) and peripherally-inserted central catheters (PICCs) breach the skin and provide a potential avenue for external micro-organisms to invade the tissue or bloodstream. All IVDs are associated with a risk of both local and systemic catheter-related bloodstream infection (CRBSI). Few studies have been conducted on colonization rates of ACs and their potential to cause CRBSI. Therefore, in a preliminary study, we compared the colonization rates of ACs with CVCs which were concurrently managed in a defined cohort of patients. This study revealed that both AC colonization and CRBSI rates were comparable to those in concurrently-sited and identically managed CVCs. Therefore, ACs should be accorded the same degree of importance as CVCs as a potential source of sepsis. This observation led to the development of 3 studies to critically examine a number of aspects of this problem. Study 1: To determine the predominant mechanism of ACs colonization by comparing ACs accessing frequency to colonization rate Study 2: To determine the degree of microbial colonization on the external and internal surfaces of concurrently-sited IVDs and to establish if microbial growth is greater on a particular segment of the IVDs at the time of removal. Study 3: To determine the degrees of concordance of nursing care and management of IVDs with Centers for Disease Control and Prevention (CDC) guidelines and institutional protocols, and how the deficit in adherence to these protocols may impact on IVD colonization. There are currently three explanations for the process of microbial colonization in IVDs. The first suggests colonization by micro- organisms occurs on the outside of the catheter, either via downward colonization of micro-organisms from the patient's skin surface on the outside surface of the catheter, or via upward colonization where the micro-organisms are inoculated on the tip of the IVD at the time of insertion. The second suggests micro-organisms are introduced via the inside surface of the IVD, either via a contaminated infusate, or via contamination of the port or hub connected to the IVD. The third suggests that microorganisms are disseminated from some other part of the patient's body, and carried via the bloodstream to both the inside and outside surfaces of the catheter. A common assumption is that the more frequently an IVD is accessed, the greater the likelihood of contamination and colonization. My first study sought to determine if accessing frequency had an influence on the rate of colonization in ACs, thereby testing the influence of the second mechanism (i.e. contamination of hub or infusate) on IVD colonization. In this study we used some of the data from the prior surveillance cohort with additional data collection. No significant differences were found between the rates of accessing the ACs and their colonization when adjusted for confounding, continuous variables. Accessing frequency of an AC did not appear to be a major predisposing factor for the likelihood of colonization, suggesting that the second mechanism of IVD colonization via the intra-luminal route was less common in the context of reasonable application of aseptic practices. My next study focused on determining the degree of microbial colonization on the external and internal surfaces of concurrently-sited IVDs, and to establish if a relative difference in microbial growth existed on a particular segment of the IVD at the time of removal. This involved determining the colony count at six different sites on each individual IVD, allowing repeated-measures comparison of each IVD with itself. Degree of colonization was greatest at the proximal, external surface of the intravascular segment of all IVD types compared to the middle or distal segments. Overall degree of colonization on the IVDs' internal surfaces was also less than on the external surfaces. This suggests that the wound site created by IVD insertion may be a significant source of colonization and CRBSI. This finding raised the question if IVD wound-site care practices might contribute to the likelihood of colonization. It is apparent that IVD colonization is caused by multiple factors, one being the environment in which these IVDs are managed and cared for on a daily basis. Practice guidelines and institutional infection control protocols provide a reference point for nurses involved with the care and management of IVDs to implement best practice. However, little is known about how closely nurses adhered to the guidelines and protocols when caring and managing IVDs, and if any variations in practice contributes to increased microbial colonization in IVDs. Therefore, the final study sought to determine the degree of concordance of current nursing practice to evidence-based practice guidelines, as a proxy for actual adherence to protocols, and how partial or non-adherence to protocols may impact on colonization. This study showed that there was less than ideal adherence to practice protocols, and that for some aspects of practice, adherence to protocol by intensive care unit nurses (who manage IVD care daily), was less than those who had less experience of IVD care. Clearly, nurses had different preferences for sourcing advice and information about IVD care practices. Future research would be required to determine whether this differential adherence to protocols and guidelines was associated with poorer outcomes, better outcomes, or no outcome differences. In summary, the major findings of this work are: 1) Establishing that AC colonization rates and CRBSI rates were similar to CVCs, reiterating the need to accord the same degree of importance to ACs as CVCs as a potential source of sepsis. 2) Dispelling the notion that the more frequently an IVD is accessed, the greater the likelihood of contamination and colonization. 3) IVD colonization via the intra-luminal route was less common when compared to the mechanism of microbial colonization on the external surface of the IVD. 4) Microbial colonization is heaviest on the external surface of the proximal segment of all IVD types compared to the middle or distal segments, and that overall degree of colonization on the IVDs' internal surfaces was also less than on the external surfaces. 5) Discrepancies in concordance between the CDC guidelines and current nursing practice exist 6) A knowledge-practice gap exists because the access to evidence-based protocols intended to provide vital information and guide nursing practice may be hindered by the choice of end-users who may not use these protocols.