Unit 4: Hemodialysis Devices

Diffusion clearances are dependent upon.....

1) Blood flow rates 2) Dialysate flow rates 3) Membrane surface area

venous pressure

Blood going back into the body

Servo Proportioning

Conductivity sensors check the total ion concentration of the dialysate electronic circuits continually adjust eh water and concentrate to achieve the correct level.

Dialyzer Membrane : Cellulosic are ....

Cotton-based materials spun into hollow fibers ( uncommonly used today) Molecular weight cut offs in the range of 3,000 Da Lease adsorptive, so lease biocompatible

Proportioning systems can make dialysate in two ways. They are:

Fixed Ratio pumps Servo-controlled mechanisms

ultrafiltration coefficient

How much water will be removed

Blood Leak Detector

The blood leak detector is an alarm system on the hemodialysis delivery system. It checks used dialysate for blood that would mean a leak in the membrane. The dector shines a beam of light through the dialysate and into a photocell.

blood pump

The blood pump is part of the hemodialysis delivery system. It pushes the patient's blood through the extracorporeal circuit at a fixed rate of speed. During a treatment, the blood tubing is threaded beteen the pump head and rollers. the rollers move blood through the circuit and back to the patient.

Hemodialysis Delivery System

The delivery system is a machine hat has a blood pump, dialysate delivery system, and safety monitors. The blood pump moves blood from the patients access through the dialyzer and back to the patient.

Conductivity

The dialysate proportioning system test the conductivity of the dialysate. A pair of electrodes or sensor cell are placed in the dialysate. The machine applies a charge and measures the current. This tells us the total ion level of the dialysate.

dialysis machine

The machine used to remove urea and excess mineral ions from the blood when the kidneys fail. Mixes dialysate and controls/monitors the whole treatment.

clearance

The rate of solute removal

Ultrafiltration (UF) Control

Water removal depends on TMP (transmembrane pressure) two kinds 1-flow metric UF control 2-Volumetric UF control

The Delivery system is

a HD hemodialysis machine that mixes dialysate, pumps blood and monitors systems to ensure safe treatment.

DIALYSATE BICARBONATE(HCO3)

a buffer that helps maintain a constant p H. helps neutralize acids that builds up in the blood when the failed kidney can't excrete them. use to restore the body buffer.

DIALYSATE POTASSIUM(K)

a major electrolyte in the intracellular fluid, essential to nerve conduction including heart function. normal serum potassium levels are 3.5-4.5 meq/L

Dialyzer Membrane : Modified Cellulose are...

an improvement over standard cellulose. The hydroxyl groups is replaced with cellulose acetate MW cutoff's is of 15,000 Da In general, more biocompatible than cellulosic membranes but less than synthetic

TRANSDUCER PROTECTORS

are small plastic caps with filters inside.

dialyzer

artificial kidney; contains a semipermeable membrane through which particles of a certain size can pass

VOLUMETRIC UF CONTROL

balancing chamber systerms assures that equal amount of fluid enter and exit the dialyzer. 2 equal chambers are each divided by an elastic membrane.

arterial pressure

between the arterial needle and the blood pump

Dialyzer Characteristics

biocompatibility membrane surface area molecular weight cutoff ultrafiltration coefficient mass transfer coefficient clearance

extracorporeal circuit: components are...

blood tubing transducer protectors blood pump pressure monitors air detectors heparin system

VOLUMETRIC PROPORTIONING

concentrate and water are mixed using fixed proportion pumps and set volumes of concentrate and water are sent to mixer chamber.

The monitoring system: The dialysis machine monitors dialysate and the blood circuits for:

conductivity temp flow rate blood leaks pH

servo-controlled mechanisms

conductivity sensors check the total ion level of the mixture. Electronic circuits compare the conductivity to what the doctor prescribes. The circuit adjust as needed. once mixed, the dialysate is checked for conductivity, temp, pressure and flow rate.

heparin pump

connected to the heparin infusion line, which is part of the extracoporeal tubing, it consists of a syring holder, a piston and an electric motor and is used to continuously deliver precise amounts of heparin during dialysis

dialyzer components

contains hollow fibers in a plastic housing, blood compartment is inside the fibers, dialysate compartment is outside the fibers. the header directs blood flow into the fibers.

The monitoring system: dialysate flow rate

controlled by the flow pump. can usually be adjusted between 0-1,000 ml/min higher flow rates improve dialyzer efficeinces. the flow rate is usually displayed on the machine.

fixed ratio pumps

diaphragm or piston pump brings set volumes of concentrate and water to a mixing chamber.

(TMP) transmembrane pressure is

difference in pressure between blood and dialysate compartments

the monitoring system: conductivity measurement

electrical current is sent from one probe to another. the more dissolved electrolytes the more electricity will pass the higher conductivity.

DIALYSATE CALCIUM(Ca++)

found in both intracellular and extracellular fluid. builds bones and teeth, aids muscle contraction, nerve conductions, and blood clotting. the normal range is 4.5 to 5.5 mEq/L. dialysate level is 2.4 to 3.5 mEq/L

Acid concentrate

has electrolytes sodium, potassium, magnesium, calcium, chlorides + glocuse and acetic acid.

bicarbonate concentrate

has sodium bicarbonate and sometimes sodium chloride.

membrane surface area

how large the membrane is

Biocompatibility

how much a membrane is like the human body

Mass transfer coefficient

how well a solute will pass through the membrane

Proportioning system

in Proportioning system, dialysate is made by mixing fresh concentrate ( bicarb and acid) with fixed amounts of trated water. mixes water, acid bicarb, concentrates

FLOW METRIC CONTROL UF

in line flow measuring devices placed before and after the dialyzer so the same amount of fluid enters and leaves. seperate pump remove precise amount of water.

DIALYSATE CHLORIDE(Cl)

levels related to the other electrolyte, disassociated in dialysate as separate molecules, dialysate chloride levels are 100-124 mEq/L

Dialyzer: synthetic are

made of plastic MW cut off around 15,000 Da Most adsorptive, so most biocompatible.

The monitoring system: temperature control

maintain dialysate in the physiologic range. a temperature >42 degree celcius denatures protein and causes hemolysis. a temperature <35 degree celcius may produce chilling and slow diffusion.

The monitoring system: blood leak detector

monitors for ruptures in the dialyzer membrane if the fiber breaks the patients can loose blood, and have unsterile dialysate in contact with their blood.

DIALYSATE GLUCOSE(c6h12o6)

often added to dialysate to increase osmolality and aid water removal. can help minimize loss of serum glucose and reduce muscle breakdown.

The monitoring system: pH measurement

pH measures how acidic or alkaline a solution is: 7 is neutral, >7 is alkaline base, <7 is acidic. normal pH of blood is 7.35 - 7.45, dialysate normal range is 6.9-7.4 and should be very close to the blood p H.

Dialysate: Na ( Sodium) is

primary electrolyte in the serum and interstitial fluid in the blood stream in the highest concentration normal level in blood is 135-145 mEq/L

air detectors

senses tiny air bubbles in the venous blood line if triggered, gives a visual and audible alarm, stops the blood pump and clamps the venous line.

Membranes are made of

synthetic ( man made) modified cellulose (containing cellulose, a plant fiber)

molecular weight cutoff

the solute size that can pass through the membrane

DIALYSATE MAGNESIUM(Mg++)

vital to muscle, nerves and carbohydrate use. normal level serum are 1.4 to 2.1 mEq/L