Faculty Peer Reviewed
An 82-year-old man is admitted to the intensive care unit with fevers, hypoxic respiratory failure and hypotension. He is intubated and resuscitated with intravenous fluids. A central venous catheter is placed via the internal jugular vein. A chest x-ray showed a right lower lobe infiltrate and he is treated empirically with antibiotics for pneumonia. Blood cultures grow out S. pneumoniae. After four days he is successfully extubated. The night following extubation, the patient has a fever of 100.8 without hemodynamic instability. Peripheral blood cultures are drawn and his central venous catheter is removed. The next morning, during rounds, a debate ensues regarding whether the catheter tip should also have been sent to the microbiology lab to be cultured. What is the evidence for and what are the current recommendations regarding the culturing of central venous catheter tips?
The central venous catheter has an essential role of the field of critical care medicine, yet, as a foreign body, its use is associated with an increased risk of infection. While much effort has been devoted to improving aseptic techniques for central line insertion,over 250,000 blood stream infections each year are believed to be attributable to catheters. Furthermore, due to substantial variations in retrieving, culturing, quantifying and subsequently defining catheter infections, there are many methodological differences between the experimental studies that investigate this topic. This article will highlight and evaluate the expert recommendations regarding catheter tip cultures, the evidence behind those recommendations and other studies that have been performed in this field.
In 2009, the Infectious Disease Society of America (IDSA) proposed that the diagnosis of a catheter related blood stream infection (CRBSI) require that a peripheral blood culture grow the same organism as a concurrently retrieved catheter tip culture. Other possible criteria for CRBSI include microbiologic concordance between two positive blood cultures where one is drawn from the catheter hub and the other is drawn from a peripheral vein. While the exact criteria for meeting positive results remain unresolved, if blood cultures drawn from the catheter produce microbiologic colonies more rapidly or in greater quantitative degree than cultures from peripheral blood, this is believed to serve as evidence of catheter infection. As these techniques do not require removal of the catheter to be performed, they are considered catheter-sparing diagnostic methods and are, respectively, termed “simultaneous quantitative blood cultures” and “direct time to positivity” (DTP).[3,4,5] Further discussion of their utility, or related techniques for diagnosing CRBSI, is beyond the scope of this brief review.
In their 2009 guidelines, the IDSA recommended that, “catheter cultures should be done when a catheter is removed because of suspected [CRBSI].” The most widely accepted technique for culturing central venous catheters was described in 1977 in a seminal paper by Maki et al and is known as the semi-quantitative culture method. Using this technique, the catheter tip is rolled over a culture dish and microorganism burden is indirectly quantified. In this study, 250 catheter tips were cultured of which 25 grew greater than 15 colony-forming units. Of these catheters, four were removed from patients who ultimately developed bacteremia. Popular for its ease of use, this article has been widely cited to support the use of this method to determine, in a clinical situation suspicious for bacteremia, whether the catheter could be implicated as the source. The premise of subsequent studies that sought to evaluate catheter tip infections was that early and precise identification of the causal organism should improve clinical outcomes. Unfortunately, randomized controlled trials have not been performed to support that premise. Of the studies cited in the 2009 IDSA guidelines regarding catheter tip cultures [7,8,9], none evaluated whether the information obtained from culturing catheter tips had any significant clinical impact on patient outcomes.
Alternatively, the utility of this practice was evaluated in a 1992 study by Widmer et al, in which 157 consecutive catheter tips were cultured order to determine whether the results had an impact on patient management. The authors assessed whether results prompted a change in, or the initiation of, an antibiotic regimen. While the authors determined that 4% of catheter culture results led to changes in patient management, the clinical significance of these results were found to be “questionable or even misleading.” The authors concluded that management of catheter infection was driven primarily by peripheral blood culture results and that catheter tip cultures contributed no benefit.
In a 2009 publication, a retrospective analysis of 120 septic patients evaluated 238 retrieved and cultured catheter tips. In 5.5% of all catheters tested, blood and catheter tip cultures grew concordant organisms but 48.4% of all catheters grew positive cultures. The associated positive and negative predictive values of a catheter culture result were calculated to be 11% and 91%, respectively. This low positive predictive value of a positive catheter tip culture was consistent with the results of the Widmer study. Based on these findings, and in consideration of the ultimate clinical impact and associated costs of the practice, catheter cultures were discontinued in the hospital where this study was performed. A smaller study examined whether catheter tip cultures could predict the likelihood of clinical bacteremia and the authors concluded that culture results from catheter tips provide minimal clinical benefit and are processed at considerable expense of time and effort by the laboratory.
The authors of these studies concluded that the results of catheter tip cultures are unlikely to significantly change clinical management. One reason for this is because the removal of a central venous catheter often results in the resolution of CRBSI, regardless of use of antibiotics, while alternate sources are often found when infections do not quickly resolve. In addition, as removal of the catheter is a prerequisite of tip culture, the necessary action precedes the desired outcome.
Typically, in a febrile patient with an indwelling catheter, clinically significant catheter infections will be detected by positive blood cultures and effectively ruled out by negative blood cultures. When catheter infection is suspected, while antimicrobial therapy usually is given adjunctively, there is general agreement that catheter removal is an absolute necessity. When catheter infections are suspected, studies seem to suggest that that management based on peripheral blood cultures and clinical assessment leads to outcomes as good as or better than when central venous catheters are cultured  and that no laboratory test is reliably better than management guided by clinical judgment.
Dr. Todd Cutler is an associate editor, Clinical Correlations
Peer reviewed by Howard Leaf, MD, Assistant Professor, Department of Medicine (ID), NYU Langone Medical Center
Image courtesy of Wikimedia Commons
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