Exploration of the patterns of microbial colonization of intravascular devices in severely ill patients
Koh, DB (2011) Exploration of the patterns of microbial colonization of intravascular devices in severely ill patients. PhD thesis, University of Tasmania.
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
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
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
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.
|Item Type:||Thesis (PhD)|
|Additional Information:||Copyright © the Author|
|Keywords:||microbial colonization in intravascular devices|
|Deposited By:||ePrints Officer|
|Deposited On:||09 Dec 2011 12:29|
|Last Modified:||16 Mar 2012 14:50|
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