Page 859 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

590 PART 5: Infectious Disorders

bacteremia. Using quantitative insertion-site cultures, the presence of
≥10 cfu/mL per 25 cm has been strongly associated with the presence
3
2
Hands of of significant catheter colonization.
medical personnel Once microorganisms gain access to the catheter tip, they act as a
nidus for further colonization because of a loosely formed fibrin sheath
with biofilm formation that develops around the distal portion of the
Hub cannula. This biofilm sheath acts as a reservoir within which micro-
colonization organisms can multiply and be shielded from the body’s normal host
defense mechanisms. The presence of grossly visible thrombus forma-
Contaminated tion on the catheter tip is also highly correlated with the presence of
Patient’s fluid bacterial colonization.
skin microflora
MICROBIOLOGY

The species of the microorganism causing a bacteremia is frequently an
important clue suggesting the intravascular device as the source of the
bacteremia. Coagulase-negative staphylococci (mainly Staphylococcus
epidermidis) and Staphylococcus aureus are the most frequently encoun-
Contaminated Hematogenous tered organisms causing cannula-related infections. These two species
on insertion spread
account for well over 50% of all cannula-related infections. Enteric
gram-negative bacilli are the next most frequent group of causative organ-
FIGURE 66-1. Potential sources for contamination of intravascular devices.
isms, followed by yeast, especially Candida albicans. Other less commonly
identified organisms include Enterococcus species, Bacillus species,
Pseudomonas species, Corynebacterium jeikeium, and Malassezia furfur.
of infusate causing central catheter–related bacteremia is also a very The frequency of Enterococcus species as a cause of bacteremia associated
uncommon problem, with an estimated incidence of less than 1 per 1000 with CVCs has increased significantly over the last two decades. 7
cannula-related septicemias. Most are reported in epidemics occurring as Studies using electron microscopy have demonstrated that virtually
a result of the exposure to a common source of microbial contamination all indwelling CVCs are colonized by microorganisms embedded in a
such as multidose vials, administration sets, or contaminated water-bath biofilm matrix, most often originating from the endogenous flora of the
warmers. The risk of fluid becoming extrinsically contaminated is related skin at the catheter entry site. 48
to the duration of infusion through the administration set. Most hospitals Unusual isolates such as Enterobacter species, Burkholderia cepacia,
now have policies that require replacement of the entire delivery system Chryseobacterium species, and Stenotrophomonas and Acinetobacter spe-
every 72 hours, which represents one of the most important control mea- cies are uncommonly found as a cause for device-associated infection and
sures for reducing the complications of contaminated infusates. Similar should suggest the possibility of a contaminated infusion product or a com-
to intrinsic contamination, hematogenous seeding of the catheter tip with mon environmental reservoir. 49,50 A summary of the organisms commonly
consequent bacteremia is considered to be an uncommon event. associated with device-associated bacteremia is given in Table 66-3.
The majority of cannula-related bacteremias are thought to result from
local endogenous microflora colonizing the skin at the insertion site and/
or the transcutaneous wound 7,29,43,44 that migrate along the subcutaneous
tunnel, colonize the subcutaneous portion of the catheter, and then finally
colonize the tip of the catheter. Another mechanism is colonization of the TABLE 66-3 Frequently Encountered Microorganisms Associated
internal surface of the catheter hub, with subsequent colonization of the With Device-Associated Bacteremia
internal surface of the catheter and eventual colonization of the catheter Source Microorganisms
tip. 45-47 This colonization could occur as a result of obligate manipulations Peripheral venous catheters Coagulase-negative staphylococci
of the connection during tubing replacements or improper connection.
After the hub has been contaminated, the microbes would be carried S aureus
intraluminally, reach the catheter tip, and colonize the fibrin sheath. The Candida species
origin of these microorganisms colonizing the hub is often the hands of Bacillus species
those manipulating the hub rather than the flora of the patient’s skin. This
latter mechanism of catheter tip colonization is considered an important Malassezia furfur
contributor to intraluminal colonization of long-term catheters. 45-47 Peripheral arterial catheters Klebsiella-Enterobacter species
Other routes of infection including hematogenous seeding from a distant Serratia species
focus of infection or, rarely, contaminated infusate are considered to be
responsible for 5% or less of catheter-related infections. 7 Coagulase-negative staphylococci
Studies of central-line infections (short indwelling insertion times) S aureus
using molecular subtyping techniques to differentiate the different Central venous and arterial catheters Coagulase-negative staphylococci
strains of infecting and colonizing organisms have demonstrated that S aureus
approximately 80% of the microorganisms from distal catheter tips are
concordant with organisms present on the skin at the catheter insertion Enterococcus species
site. The source of the remaining organisms was either contamination Candida species
of the catheter hub, hematogenous colonization from remote sites, or Corynebacterium jeikeium
unknown sources. Of episodes of catheter-related bacteremia, concor-
dance of organisms at the catheter insertion site, the catheter tip, and the Klebsiella-Enterobacter species
blood varied between 86% and 100%. Bacillus species
It also has been shown in several studies 15,20,43 that heavy coloniza- Trichophyton beigelii
tion at the catheter insertion site is strongly associated with significant
catheter colonization, which in turn is associated with catheter-related Malassezia furfur

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