Page 108 - Biomedical Engineering and Design Handbook Volume 2, Applications

OVERVIEW OF CARDIOVASCULAR DEVICES 87

(Marin et al., 2000). The meta-analysis revealed a significant decrease in the number of catheter-related
infections for all experimental catheters versus standard devices, plus a significant reduction in
infections for catheters employing antimicrobial systems other than silver sulfadiazine and
chlorhexadine when compared to those systems (Marin et al., 2000). A randomized trial comparing
bacterial colonization and catheter-related bloodstream infection rates associated with two antimi-
crobial catheters came to a similar conclusion, with minocycline- and rifampin-coated catheters
being linked with significantly fewer events than chlorhexidine- and silver-sulfadiazine–coated
catheters (Darouiche et al., 1999). In an effort to improve handling characteristics, radiofrequency
glow discharge has been used to alter the surface properties of common catheter materials to
increase hydrophilicity (Triolo and Andrade, 1983a) and reduce friction. This latter property is
important in the double catheter systems used for some interventional procedures (Triolo and
Andrade, 1983a).

3.7.4 Management and Complications
Infection and thrombosis are common across a variety of catheter designs and applications, while
other complications arise due to the particular nature of the therapy being administered, such as
recirculation in hemodialysis. Catheter malfunction and related morbidity and mortality represent an
area where significant strides are currently being made.
Infection is a common complication associated with intravenous catheters and represents the
primary cause of hospital-acquired bloodsteam infection (Valles et al., 1997), resulting in signif-
icant morbidity, mortality, and consequent increase in healthcare expenditures. It has been esti-
mated that 250,000 CVC-related blood stream infections occur each year in the United States
(O’Grady et al., 2002). The preventable nature of most catheter-related blood stream infections
(CRBSI) has led to the Centers for Medicare and Medicaid Services (CMS) to limit reimburse-
ment when such infections occur during a hospitalization (Rosenthal, 2007). This approach
should increase the demand for engineered solutions to common problems plaguing health care.
Proper care and maintenance is essential for the continued functioning of a catheter, and a num-
ber of strategies have been implemented in an effort to minimize infection risk. The use of spe-
cial coatings and antimicrobial saturated devices was discussed above in the area on device
design. Careful exit site management with a dedicated catheter-care team, antibiotic flushes, and
possibly catheter tunneling can lower the risk of infection (Raad, 1998), as can the use of a totally
implantable intravascular device, which has the lowest infection rate among standard vascular
access devices (Maki et al., 2006). Tunneled catheters are fitted with a Dacron cuff that stimu-
lates accelerated healing and ingrowth of tissue distal to the insertion site, thereby providing a
host barrier to pathogen migration. In addition, antiseptic cuffs have been placed on catheters to
inhibit bacterial migration (Maki et al., 1988; Hasaniya et al., 1996) but overall results are mixed,
suggesting that infecting organisms often migrate through the luminal route or that the cuff loses
its antibiotic function over time (Sitges-Serra, 1999). In a recent meta-analysis, tunneled and
cuffed CVCs had significantly fewer CRBSIs when compared to nontunneled and noncuffed
devices (Maki et al., 2006). Once a catheter-related infection is detected, the approach to care is
dependent upon the patient condition, the number of remaining access sites, and other factors
such as the suspect organism, but the catheter is usually removed and antibiotic therapy initiated
(Mermel et al., 2001).
Thrombotic complications are common with catheter use. The development of a fibrin sheath is
a near universal occurrence on intravascular devices such as central venous (Hoshal et al., 1971) and
hemodialysis catheters, and can have a profound effect upon blood flow in the device (Trerotola,
2000). This sheath can be removed either by stripping (Crain et al., 1996; Rockall et a1., 1997) or
fibrinolytic medical therapy (Twardowski, 1998), or the catheter can be replaced to restore adequate
flow performance. Recent randomized controlled clinical trials have revealed improved long-term
outcomes with catheter exchange versus fibrin sheath stripping (Merport et al., 2000), while no out-
come differences were realized in patients randomized to either fibrin sheath stripping or throm-
bolytic therapy (Gray et al., 2000).