Page 106 - Biomedical Engineering and Design Handbook Volume 2, Applications

OVERVIEW OF CARDIOVASCULAR DEVICES 85

as dialysis (Cimochowski et al., 1990; Schillinger et al., 1991). Some experts suggest the use of the
external jugular vein prior to the use of the subclavian, particularly when chronic use is anticipated
(Weeks, 2002; Hoggard et al., 2008).

3.7.3 Device Design
Design considerations for vascular access devices include ease of handling, insertion and use, mini-
mal thrombotic and other biocompatibility-related complications, structural and operational reliabil-
ity over time, and optimization for application-specific performance issues (Canaud et al., 2000).
Three different catheter tips are shown in Fig. 3.12 to illustrate these variations in design and struc-
ture. Due to the distinct characteristics of the different treatments and agents deployed through
catheters, it is not practical to provide specific values for flow rates, pressure drops, viscosities, and
other important transport properties.
Catheter device selection is based on a number of factors, including the planned application
and placement site, duration of implantation, composition of fluids infused, and frequency of
access (Namyslowski and Patel, 1999). Vascular catheters can be divided into two general groups:
short-term, temporary catheters that are placed percutaneously; and long-term, indwelling vascu-
lar catheters that usually require a surgical insertion. Temporary catheters include short peripheral
venous and arterial catheters, nontunneled central venous and arterial catheters, and peripherally
inserted central catheters (Pearson, 1996). Tunneled central venous catheters and totally
implantable intravascular devices (i.e., ports) are used for therapies requiring long-term vascular
access (Pearson, 1996). The term tunneled refers to the placement of the catheter exit site at a loca-
tion away from the area where the vasculature is penetrated, with the portion of the catheter
between these two locations lying in a subcutaneous position. Peripheral venous catheters are the
most common devices used for intravascular access, while the nontunneled central venous catheter
is the most common central catheter (Pearson, 1996). Subcutaneous ported catheters are the

FIGURE 3.12 A selection of catheter tips is shown. The large number of applications for catheters requires
differences in hole size, number and placement, along with changes in materials, coatings, and number of
lumens.