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Hemdialysis Machine
Contents:
Hemodialysis machine
consists of :
1.Blood pump
2.Dialysate delivery
system
3.Safety
monitors
4.Options
5.System disinfection:
Function :
It circulate the blood through the dialyzer back
to the patient.
Kinds :
Presently peristaltic roller pumps which works
by progressive compressing special segments of the blood tubing are used.
Pump occlusion:
Occlusion means that the roller compress the tubing segments against the
semicircular housing sufficiently to close the lumen completely at that point.
Consistent pump flow rates require precise occlusion. Overocclusion may crack
the tubing and rupture of the pumping segment. If occlusion is incomplete, there
will be backflow of the blood with each stroke, inaccurate flow rate and red
cell damage The flow rate for adult is ~ 4 times patient body weight ml/minute,
up to 600ml/minute in high efficiency and high-flux dialysis.
Function
-Appropriate blending of concentrate and water for preparation of final
dialysate.
-To monitor dialysate for temperature, composition, and blood leak
-To control dialysate pressure or ultrafiltration rate.
-To regulate the dialysate flow rate through the dialyzer.
- Deareation of water
-Provide protective mechanisms to isolate the blood circuit and the patient from
unsafe dialysis.
-System for disinfection and cleaning
Types a.
Single batch system b.Continuous proportioning system
c.Sorbent regenerative system
a. Single batch system
(is of historic interest)
b.Continuous proportioning system (early1960s)
1.Central
:
-All the dialysis solution used for dialysis is produced by mixing the
concentrate with purified water and pumped to each machine
-Advantage : Cost effective
-Disadvantage :Not permitting dialysate composition modification
2.Individual
:
-Each dialysis machine proportions its own concentrate with the purified water.
-Advantage :
1. Permitting dialysate composition modification by selecting different
concentrate or altering the mixing ratio.
2. There is significant saving in time.
3. Less bacteriologic and chemical contamination. 4. Reduced the risk of human
error.
-Disadvantages :
a. Complex sophisticated system
b. Costly
c.Troubleshouting may be difficult and needs a factory-trained service
technician.
Methods of mixing in proportioning system
1. Matched pumps
2. Matched metering valves
3. Matched hydraulic-accumulation cylinders
4. Electronic feedback circuit. Details of mixing are beyond the scope
the Tips
c.Sorbent regenerative system
for renewing dialysate. At present it is rarely used.
Heating
-The physiological range of dialysate temperature is 36-42 c
-Temperature below 36 patients will complain of cold and uncomfortable.
-Temperature above 42 protein denature can occur and above 45 red blood cells
will hemolyze. cardiorespiratory arrest and death (from hyperkalaemia and
hypoxemia )as a consequence of overheated may occur.
Deaeration or Degassing
Water contains considerable amount of dissolved air and microbubbles. Once
negative pressure is applied and water is warmed the air comes out of the
solution as expanding microbubbles.
Bubbles causes:
1.Artifacts on conductivity, temperature sensors
and flow meters
2.When bubbles cross the membrane into the blood
foaming occur and increases potential for clot formation, hemolysis and
occlusion of the fibers.
3. It decreases the surface area of the dialyzer
4. It block the dialysate flow channels
subsequently dialysate pressure drops and the dialysate surface area
incompletely utilized for solute transport
Deareation devices uses warmers along with negative pressure (- 600 mmHg) to
bring the dissolved air out of the solution. An air trap or coalescing filter
then capture the air and vents them out.
Dialysate
pressures
The dialysate delivery system must be capable of generating positive and
negative dialysate pressures (~ - 400 to + 200).
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In dialysis machines without an
ultrafiltration controller the dialysate pump is located at the line leading
from the dialyzer to the drain. This allows the machine to create a negative
pressure in the dialysate compartment of the dialyzer. The negative pressure is
generated by partial occlusion of dialysate hose proximal to the dialyzer. To
increase the rate of ultrafiltration, negative dialysate pressures (suction
pressures) are often required. Transmembranous pressure is a resultant of the
blood compartment and dialysate compartment pressures.
·
High positive pressure is required
in situation in which ultrfiltration coefficient or the blood compartment
pressure are high to limits the rate of obligatory ultrafiltration. Higher
positive pressure (+ 350) may be necessary with high-flux membranes However,
backfiltration occurs when dialysate pressure is greater than that of blood
compartment, e.g. at the blood outlet. Transport of endotoxin fragments into the
blood in such membranes.
Dialysate
Flow
The standard dialysate flow rate is 500 ml/minute. When high-efficiency and
high-flux dialyzer are used high dialysate flow rate between 700 and 1000 is
required along with high blood flow rate. High flow rates are needed for:
1. Optimum use of dialyzer surface area for solute transport.
2.With high dialysate flow rate a positive dialysate pressure is generated which
limits the rate of obligatory ultrafiltration.
3. Safety monitors:
Monitors for blood circuit
1.Arterial pressure monitor
Locations:
Proximal to the blood pump
Function:
1. It reads the arterial pressure at the segment between the patient's needle
site and proximal to the blood pump which represent the negative
pressure created by the roller pump. 2.It identifies how much suction is being
placed on the arterial wall and guard against excessive suction on the vascular
access, e.g. .if suddenly the arterial pressure increases from 100 to 200
mmHg this could indicate clotted or dislodged needle, low patient BP or kink in
the arterial line. 3. Resistance within the needle (function of the
gauge and needle length). 4. It provide an index of vascular access blood supply
relative to the flow demand by the blood pump. 5. A guide to appropriatence of
needle placement or kink or obstruction in the blood segment between the patient
and the monitor.
Mechanism:
The pressure is monitored by mechanical or
electronic manometers (pressure transducers) . Electronic transducer is more
sensitive and have rapid response
2.Venous pressure monitor
Location:
Just distal to the dialyzer, usually attached to the top of the venous air trap.
Function:
1. It reads the venous pressure at the segment between the point after the
dialyzer and before the blood reenters the patient's body. 2. It represent the
resistance of the blood returning to the patient via the venous needle e.g.
if suddenly the venous pressure increases from 50 to 150 mmHg this could
indicate kink in the venous line, clotted air trap or the venous needle may be
clotted or maligned. Sudden dropping venous pressure occurs when the venous
needle is pulled out, wet transducer or clotted arterial chamber.3. It may
indicate venous stenosis proximal to the needle site.
Mechanism:
As in arterial pressure monitor.
3.Venous air trap and air detector
Location:
1. Just distal to venous pressure monitor.
2. Often second air trap on the arterial line is also used.
Function:
To prevent air entry into the patient or to the dialyzer. It is used also to
measure the pressure in that segment of blood circuit.
Mechanism:
When air bubbles entered the blood circuit a sensor reacted through ultrasonic
transducer or light beam by stopping the blood pump, clamping the venous line,
and activating audiovisual alarms.
Monitors
for dialysis solution circuit
1.Conductivity
Location :
Before dialysate reaches the dialyzer
Function
To guard against excessive diluted or
concentrated dialysis solution.
Mechanism :
When conductivity meter (conductivity probe) detects high or low conductivity
the machine automatically sounds an alarm and puts the dialysate into bypass
mode so that no dialysate flow to the dialyzer.
Exposure of the blood to hyperosmolar dialysate can lead to hypenatraemia and
other electrolyte disturbances. Exposure of the blood to hypoosmolar dialysate
can results in hyponatraemia and rapid hemolysis.
2.Temperature
Location:
Before the dialyzer
Function:
To avoid high temperature
Mechanism:
Through a temperature sensor, high temperature activate an audiovisual alarm
simultaneously with bypass mechanism.
3.Bypass valve or mechanism
If the conductivity or Temperature found to be out of limits a bypass valve is
activated to divert dialysate around the dialyzer directly to the drain.
4.Blood leak detector
Location :
In the effluent dialysate line
Function:
It guards against undetected blood loss during dialysis. The maximum limit to
hemoglobin present in dialysate is 70 mg/L (corresponding to blood loss of ~0.4
ml/minute ) after which the blood pump is stopped.
Mechanism:
A beam of light is directed through a column of dialysate onto a photoelectric
cell. A change in translucence and light scatter in dialysate reduces the light
received by the photocell, stopping blood pump and activating audiovisual
alarms.
5.Dialysate pressure or transmembranous monitor
Function :
To monitor the ultrafiltration with an upper limits avoids excessive level (the
usual preset range 0 to -500 mmHg). Excessive TMP may lead to rupture of the
dialyzer and secondary deareation (cause air accumulation).
Mechanism:
The monitor may have automatic or manually set limits, so that extrusion outside
the limits trigger an audiovisual alarm.
4. Options in hemodialysis machine:
1.Heparin pump
2.Bicarbonate 3.Variable sodium
4.Controlled Ultrafiltration
5.Programable ultrafiltration
6 Dialysate urea sensor [on-line Kt/V monitor] 7.Single blood pathway.
All dialysis unit s must have written policies the deal with the dialysis fluid
pathway and dialysis machine . Disinfection procedure should be done on regular
base according to manufacturer's instructions.
Target:
To control bacterial contamination. HIV, HCV and HBV viruses are known to be
inactivated by common household bleach.
Methods
1.Heat disinfection requires temperature greater than 85-90 C
2.Chemicals disinfection such as formaldehyde , sodium hydrochloride and acetic
acid
Machine surfaces, patient's chairs, surrounding furniture, equipment should be
routinely wiped with 10% bleach solution following every patient dialysis. Blood
spills should be cleaned immediately. Leak proof bags should be used to
transport linen soiled with blood or body fluid
When an alarm is activated during dialysis do
the following:
1-Identify which alarm has been activated.
2-Identify the cause.
3-correct the cause
4-Resume dialysis if safe to do so
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Problem |
Management |
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1.Power
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a. Turn the system off and on; if still no
power, check the power cord; make sure power is available
b. Check the fuse |
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2. Arterial and venous Pressure
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a. Check to see that blood
pump is running and connected properly
b. Check to see if blood
flow rate has changed
c. Determine if patient has
coughed or moved
d. Check to see if the monitor line is leaking
e. Check the blood line for kinks or leaks
f. Ensure the monitoring
lines are connected to proper drip chambers
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2.1 High venous pressure
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1-Manipulate the needle and
or the line. If the access is small, a tourniquet must be used, being
certain the blood pump is off ..Recantation with new needle if needed ,the
original one should be left in place until the end of dialysis. to avoid
undue bleeding as the patient is heparinized
2-Adjust the blood flow
rate , Proper heparnization , Treat access problem ,and Proper needle and
needling
3-Extreme care must be
exercised when dialyzing a patient with high venous pressure
-This increases the baseline
TMP and obligatory ultrafiltration will occur
-Single-needle device is
occasionally impossible to use, because with high venous pressure ,venous
return will be impaired and blood recirculation will be high
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2.2 Increase in negative pressure:
(Excessive inflow suction) |
Management of increased negative pressure:
1- Manipulation of the arterial
needle is similar to that of venous needle. In most cases the needle may
have to be replaced with the same precaution as with venous needle
2-Treat the cause.
3- Proper needling
4-Asses the access |
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3.Air detector alarm
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a-Check for air leaks around tubing joints.
b-Excessive undetected negative pressure
c-Check for unattended intravenous solution
administration.
Management of air embolism if present
a-Clamp the venous line and stop the blood
pump.
b-Place the patient in Trendelenberg
position on the left side with the
chest and head tilted downward to trap the
air at the apex of right ventricle away from the outflow tract.
c-Cardiorespiratory support ,Oxygen 100%.
d-Occasionally percutaneous aspiration of
the air foam from the heart may be necessary.
e-Other measures include IV Dexamthsone to
reduce brain edema ,Heparin /Dextran to improve the microcirculation.
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4.High Positive
dialysate pressure alarm |
a Check to see if drain is occluded or
kinked
b. Check to see if dialysate hoses are
leaking air |
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5.Low Negative dialysate pressure alarm |
Check to see if dialysate hoses are kinked
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6.HighTemperature
alarm |
a. Determine temperature of dialysate (to
dialyzer) in the line actually high
b. Check to ensure incoming water
temperature is blew 90 F |
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7.Low Temperature alarm |
a. Determine temperature of dialysate”to
dialyzer” in the line is actually Low
b. Turn the mode selector switch to
“dialyze”
c. Allow adequate time for the system to
stabilize and come to proper temperature range
d. Check to ensure incoming water
temperature is above 40 F |
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8.High conductivity alarm |
a. Check to see if water is flowing too
slowly or turn off
b. Check for kink in the concentrate out
line
c. Make sure that the system has had time
to stabilize
d. Analyze the dialysate to confirm high
conductivity at the “to dialyzer” line connection :
1.If normal, there is malfunction in the
machine itself (change it)
2.If high again concentrate should be
changed
3.Check the conductivity before resuming
dialysis
e. Be certain that the dialysate flow rate
is proper.
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9.Low Conductivity alarm |
a. Turn the mode selector switch to
“dialyze”
b. Connect the concentrate line to the
system
c. Drop the concentrate line into the
concentrate container
d. Check for kinks in the “concentrate” in
line
e. Make sure the filter on the “concentrate
in” is clean
g. Allow adequate time for the system to
stabilize
h. Change the concentrate container if it is
dry
i. If the concentrate container has not run
dry ,a sample of dialysate should sent to the laboratory for sodium and
chloride
j. Analyze the dialysate to confirm low
conductivity at drain
1.If low conductivity is
confirmed ; change the concentrate bottle (recheck again)
2.If the conductivity
still low after changing the concentrate , a different machine should be
tried
l. Be certain that the dialysate flow rate
is proper |
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10.Blood Leak alarm |
a. Make sure the blood leak
detector is clean
b. Check the effluent for
traces of blood
c .Check the dialysate lines
for gross blood leak
d. Exclude 1.bilirubin in
dialysate in jaundiced patient
2.air
bubbles in dialysate 3.dirty sensor
e. If a leak confirmed and
you can not mange the cause
1.reduce dialysate
compartment pressure to -50 mmHg to avoid bacterial entery to the blood
2.Dicontinue dialysis |
N.B. Review the previous tips and the manual for each
machine if needed.
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