HEMODIALYSIS BASICS
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The Water Supply
The water used for dialysis must be of a high quality since the
water is used to prepare dialysate.
A hemodialysis patient is exposed to several hundred liters of
dialysate per week, which is separated from the blood only by
a thin membrane.
The incoming water is therefore purified before it is used
by the dialysis machine in a reverse osmosis (RO) and
deionization units. This device uses a semipermeable
membrane that allows the passage of water but removes
most other contaminants.
Pretreatment of the water may be required before it enters
the RO unit.
• A water softener to remove water hardness, including
calcium and magnesium ions
• A carbon filter to remove chlorine and chloramines
• A sediment filter to remove particulate matter
The water should be analyzed on a regular basis, both from
a chemical and microbiological standpoint, to ensure that it
complies with relevant standards for dialysis water.
Efficiency of Hemodialysis
Note: Image is representative of facilities
that use a portable RO system.
How do we know that the prescription and the treatment are adequate?
To accomplish a satisfactory dialysis treatment, four things have to be achieved:
1. Adequate removal of excess fluid
2. Adequate removal of unwanted solutes i.e., waste products
3. Correct electrolyte (salt) imbalances
4. Restore buffer (bicarbonate) balance
Note: The time the blood pump is stopped as well as the time the dialysate is bypassed will reduce the
effective treatment time.
Removal of excess fluid
Accurate weight and assessment of fluid balance must be performed prior to initiating a treatment.
The fluid volume to be removed, the UF goal, is calculated from the weight gain since the last treatment,
to which is added the volume of the fluids used during the session as well as any additional infusions.
The target weight is called dry weight. This is the lowest tolerated post dialysis weight (achieved via gradual
change in post dialysis weight) at which there are minimal signs or symptoms of hypovolemia or hypervolemia.
When the UF goal is set, the machine can calculate the required UF rate by considering the treatment time,
normally between 3 and 4 hours for conventional HD.
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