Civil Engineering Reference
In-Depth Information
of the membrane. h e dialysis solution has levels of minerals like potassium and cal-
cium that are similar to their natural concentration in healthy blood. For another solute,
bicarbonate, dialysis solution level is set at a slightly higher level than in normal blood,
to encourage dif usion of bicarbonate into the blood, to act as a pH buf er to neutral-
ize the metabolic acidosis that is ot en present in these patients. h e cleansed blood is
then returned via the circuit back to the body [5]. Ultrai ltration occurs by increasing
the hydrostatic pressure across the dialyzer membrane. h is usually is done by applying
a negative pressure to the dialysate compartment of the dialyzer. h is pressure gradi-
ent causes water and dissolved solutes to move from blood to dialysate, and allows the
removal of several liters of excess l uid during a typical 4-hour treatment. h e levels
of the components of dialysate are typically prescribed by a nephrologist according to
the needs of the individual patient. In peritonealdialysis, wastes and water are removed
from the blood inside the body using the
peritoneal membrane
of the peritoneum as
a natural semipermeable membrane. Wastes and excess water move from the blood,
across the peritoneal membrane, and into a special dialysis solution, called dialysate, in
the abdominal cavity which has a composition similar to the l uid portion of blood. h e
therapy is usually performed 3 times, in rare cases just 2 times, weekly at a dialysis cen-
ter or at home. With a possible duration of 3-8 hours, the therapy usually lasts about 4
hours. h e patient requires a vessel access mechanism from where the blood is removed
via a bloodline system with the help of a dialysis machine, routed through a dialysis
i lter, cleaned and supplied back to the patient. h e therapy restores the blood's renal
values (toxins, electrolytes, etc.) to the normal levels, enabling the patient to spend at
least two days without any further treatment. In addition to dialysis, the patient is reli-
ant on medicinal treatment and must observe dietary recommendations.
In the U.S.A., hemodialysis treatments are typically given in a dialysis center three
times per week (due to Medicare reimbursement rules in the U.S.A.); however, as of
2007 over 2,500 people in the U.S.A. are dialyzing at home more frequently for various
treatment lengths [6]. Studies have demonstrated the clinical benei ts of dialyzing 5 to
7 times a week, for 6 to 8 hours. h is type of hemodialysis is usually called "nocturnal
daily hemodialysis," shown by a study to signii cantly improve both small and large
molecular weight clearance and decrease the requirement for taking phosphate binders
[7] . h ese frequent long treatments are ot en done at home while sleeping, but home
dialysis is a l exible modality and schedules can be changed day to day, week to week.
In general, studies have shown that both increased treatment length and frequency are
clinically benei cial. Hemodialysis was one of the most common procedures performed
in U.S. hospitals in 2011, occurring in 909,000 stays (a rate of 29 stays per 10,000 popu-
lation) [8] .
In 1861, h omas Graham, Professor of Chemistry at Anderson's University in
Glasgow, who i rst coined the term dialysis, demonstrated that crystalloids were able to
dif use through vegitable parchment coated with albumin and predicted that his i nd-
ings might be applicable to medicine [9]. And the term dialysis was i rst routinely used
for scientii c or medical purposes in the late 1800's and early 1900's, pioneered by the
work of h omas Graham. h e i rst mass-produced manmade membranes suitable for
dialysis where not available until the 1930's, based on materials used in the food pack-
aging industry such as Cellophane. In 1993, Abel, Rowntree and Turner published the
historical description of dialysis, when they dialyzed anesthetized animals by directing
