Hemodialysis Devices: Dialysate

Thursday, October 21, 2010

Hemodialysis Devices: Dialysate

Article by a Renal Nurse

Labels: Hemodialysis Devices

Sections of Dialysate

Image Source: lhsc.on.ca

Bicarbonate (HC03)

PURPOSE OF DIALYSATE

• Dialysate is a fluid that helps remove uremic wastes, such as urea and creatinine, and excess electrolytes, such as sodium and potassium.
• Dialysate can also replace needed substances, such as calcium and bicarbonate, which helps keep the body's pH balance.
• During a treatment, the patient's blood is on one side of the membrane, in the blood compartment, The dialysate is on the other side, in the dialysate compartment. Dialysate and blood never mix, unless the membrane breaks.
• Dialysate is prescribed to have a desired levels of solutes the patient needs and none of the ones that must be removed completely.
• The osmolality (solute particle concentration) of dialysate should closely match the blood to keep to much fluid from moving across the membrane.
• The concentration gradient created decide the diffusion rates of each solute across the membrane.
• Unwanted solutes leave the blood and move into the dialysate; desired solutes stay in the blood.
• Some solutes are added to dialysate in amounts that can cause them to enter the patient's blood. Most often, these are sodium, bicarbonate, and chloride.

COMPOSITION OF DIALYSATE
• The doctor prescribes the dialysate. Dialysate starts out as two concentrated salt solutions: acid and bicarbonate.
• The two concentrates are diluted with precise amounts of treated water to make the final dialysate. The concentrates come in three different formulations.
• Because there are three formulations, care must be taken to match the right acid concentrate with the right bicarbonate concentrate.

Acid Concentrate

Sodium chloride
Potassium chloride
Calcium chloride
Glucose
Acetic acid (to lower thedialysate's pH)

Bicarbonate Concentrate
Sodium bicarbonate
In some cases, sodium chloride

COMPOSITION OF DIALYSATE
• The Association for the Advancement of Medical Instrumentation (AAMI) has set standard symbols to match the concentrates.
• Today, almost all of the hemodialysis machines can use any of the formulations.
• When the concentrates are diluted with the prescribed amount of water, they will have the right concentration of electrolytes.
• Electrolytes are vital for cell function.

Substance ------------------------------ Concentration in Dialysate
Sodium ------------------------------ 135 to 145mEq/L
Potassium --------------------------- 0 to 4 mEq/L
Calcium ----------------------------- 2.5 to 3.5 mEq/L
Magnesium -------------------------- 0.5 to 1.0 mEq/L
Chloride ----------------------------  100 to 124 mEq/L
Bicarbonate ------------------------ 32 to 40 mEq/L
Glucose ---------------------------- 0 to 250 mg/dL

Sodium (Na+)
• Is a major electrolyte of the body's blood plasma and interstitial (between the cells) fluid.
• Fluid and solutes must be in the plasma to be removed by dialysis.
• Normal sodium concentration in the blood is from 135-145mEq/L.
• Sodium concentration in the dialysate is most often kept in the same range.
• Dialysate delivery systems can adjust the dialysate sodium level during a treatment. The dialysate sodium level is changed according to a doctor's prescription. This is called sodium modeling.
     • It has been shown to create more efficient fluid shifts in the body, to remove fluid taster
     • Provides for better control of blood pressure and fluid removal
     • However, it can increase thirst and body weight, and hypertension between dialysis treatments

Potassium (K+)

• Is a major electrolyte of the intracellular fluid.
• The body keeps precise amounts on both sides of cell membranes to send nerve signals.
• Normal plasma potassium level is from 3.5 - 5.5 mEq/L.
• Potassium in the dialysate ranges from 0-4 mEq/L based on the patient's needs.

Magnesium (Mg++)
• Is vital to the nerves and muscles.
• It also triggers enzymes that are key to carbohydrate use.
• Normal plasma magnesium level is from 1.4-2.1 mEq/L.
• The magnesium range in dialysate is 0.5 - 1.0 mEq/L

Calcium (Ca++)
• Is Found in the body in extracellular (outside the cells) and intracellular (inside the cells) fluid.
• It builds bones and teeth, helps musjies move, is needed I'or blood clotting, and helps send nerve signals.
• The normal range of calcium in the plasma is 8.5 -10.5mg/dL(4.5-5.5mEq/L)
• Dialysate calcium is most often 2.5 - 3.5 mEq/L

Chloride (CI-)
• The concentration of chloride in dialysate depends on the contents of chemicals such as sodium chloride, potassium chloride, magnesium chloride, and calcium chloride.
• Normal plasma chloride levels are 98 - 111 millimoles per liter (mM/L)
• Dialysate chloride ranges from 100-124 mEq/L

Glucose (Cf,Hi206)
• Glucose may be added to dialysate to prevent loss of serum glucose and to reduce catabolism (muscle breakdown)
• Dialysate glucose levels may range from 0 - 250 mg/dL
• The glucose in dialysate can be two fo three times higher than in normal (70-105 mg/dL).
• This means that dialysate with glucose has an osmotic (water-pulling) effect that aids UF.

Bicarbonate (HCOa)
• Bicarbonate is a buffer - a substance that tends to maintain a constant pH in a solution, even if an acid or base is added.
• Healthy kidneys keep the body's pH within the very tight limits that cells need to survive. The kidneys do this by making and regulating bicarbonate.
• Bicarbonate is added to dialysate to help maintain , patients' pH.

Bicarbonate (HC03)

• Is used by the body to neutralize acids that are formed when cells metabolize proteins and other foods used for fuel.
• People with CK.D can't excrete enough acids in the urine, so they are in constant state of metabolic acidosis (i.e., having too much acid in the blood)
• in dialysate, bicarbonate is used to replace the body's stores of buffer.
• Can reduce dialysis-related problems like hypotension, muscle cramps, nausea, and fatigue after treatment.