Biomedical Engineering Reference
In-Depth Information
internal diameter) and dialysate is pumped into the cylinder and across the tiny
hollow fibers. This technology replaced the traditional membranous tubes and flat
membranes with a number of capillary-sized hollow membranes. The development
of the related industrial manufacturing technology by Dow Chemical allowed the
production of large numbers of dialyzers at a reasonable price. The typical hollow-
fiber dialyzers of today, which are equipped with a more effective and better-tol-
erated membrane made primarily from synthetic polymers, are still based on early
concepts developed by Abel. As the clinical use of hemodialysis became increas-
ingly widespread, scientists were better able to investigate the unique attributes of
patients with chronic kidney disease. Scientific discoveries in the transport of sub-
stances across membranes accompanied the technological refinement of dialyzers
and began to include dialysis-specific research. Mathematical models were devel-
oped to describe the hemodialysis process and performance characteristics. In con-
trast to the early years of dialysis, the lack of adequate treatment methods or tech-
nologies is no longer a challenge in the treatment of renal patients. Development of
physiological models of the dialysis process that resemble the functionality of the
body has also played a significant role in improving the performance of the dialyz-
ers in addition to helping the physicians match dialysis therapy to the individual
needs of the patient. These models (some discussed in Chapter 8) make it possible
to analyze the course of treatment and to predict the effect of dialysis procedures.
These efforts made a quantitative description of dialysis possible and allowed the
development of dialyzers with clearly defined characteristics. The composition of
the dialysate is also adjusted to retain desired components in the blood and cause
undesired components to diffuse with the dialysate. Many new membrane materi-
als are also available in high-flux modifications.
As minimally invasive medical procedures evolve, the design requirements for
the medical devices used in them become increasingly complex. In 1964, Silastic
peritoneal catheters suitable for long-term placement were developed. Further, ma-
chines to manufacture and deliver sterile dialysis fluid and to control its inflow
and outflow from the peritoneal cavity were developed. Several such devices have
become commercially available since that time. Peritoneal dialysis is frequently a
better neonatal option to aid babies with compromised renal function than hemo-
dialysis because smaller infants cannot afford to lose the blood volume necessary to
prime the hemodialysis blood circuit. Dialy-Nate (Utah Medical Products) is a pre-
assembled and closed peritoneal dialysis kit (Figure 1.3) specifically designed for
the neonatal and pediatric use. Because it is preassembled, Dialy-Nate is safer and
more effective than assembling separate tubing and components. The total priming
volume is 63 mL, which includes 58 mL from the bag spike to the catheter and an
additional 5 mL from the catheter to the finely graduated dialysate meter. Dialysis
can begin much sooner since nursing and technician time is not spent researching
hospital dialysis assembly procedures. However, the present challenges are multi-
fold and come from the large number of patients requiring dialysis treatment, the
complications resulting from years of dialysis treatment, and a growing popula-
tion of patients that presents demographic as well as medical challenges. Efforts to
relate the patient's outcome to the dialyzer's performance have been difficult and
ongoing since 1971.
