22 The Machine & Water Treatment Practice Questions & Answers
Every The Machine & Water Treatment practice question from the Dialysis Technician Practice Test, with the correct answer and a short explanation.
Start practice test →1. During treatment the arterial pressure reading, which is normally negative, drifts from -80 mmHg to -240 mmHg and alarms. What is the most likely cause?
- A.The machine cannot pull blood freely from the access: the arterial needle is against the vessel wall or infiltrated, the line is kinked or clamped, or the pump speed is set too high for the access✓ Answer
- B.Air has been detected in the venous line
- C.Blood is clotting in the venous drip chamber
- D.The bicarbonate concentrate container has run empty
The arterial pressure monitor sits before the blood pump, so it measures the suction the pump applies to the access. Anything that restricts inflow forces the pump to pull harder, which drives the reading more negative. The technician checks the needle position and the line for kinks or clamps, reduces the pump speed according to facility protocol, and notifies the nurse; venous-side problems raise the venous pressure instead.
Source: NNCC CCHT content outline, Technical practice area (extracorporeal circuit pressure monitoring)Report a problem with this question
2. Over the course of a treatment the venous pressure has risen steadily from 120 mmHg to 250 mmHg with no change in blood pump speed. What does this change most likely indicate?
- A.The dialysate temperature is too low
- B.The patient's blood pressure has fallen
- C.The arterial needle has infiltrated
- D.An obstruction to blood returning to the patient, such as clotting in the dialyzer or venous chamber, a kinked or clamped venous line, a malpositioned venous needle, or stenosis in the access✓ Answer
Venous pressure is measured after the dialyzer and is normally positive because the blood is being pushed back into the access. Anything that narrows the return path raises the pressure needed to push the same flow through it, so a steadily rising venous pressure points to outflow obstruction. The technician inspects the circuit and access, follows facility protocol, and reports the finding to the nurse.
Source: NNCC CCHT content outline, Technical practice area (venous pressure monitoring and access outflow)Report a problem with this question
3. The venous pressure alarm sounds and the reading has dropped abruptly to near zero while the blood pump is still running. What should the technician do first?
- A.Give the patient a bolus of normal saline
- B.Stop the blood pump, clamp the lines, and immediately inspect the venous needle and all connections for separation or dislodgement, then call the nurse✓ Answer
- C.Silence the alarm and lower the venous pressure alarm limit so the treatment can continue
- D.Increase the blood pump speed to bring the pressure back up
A sudden loss of venous pressure means the circuit is no longer pushing against a resistance, which suggests the venous needle has come out or a connection has separated. Because blood loss through a dislodged venous needle can be rapid and is not reliably detected by the pressure alarm, the pump must be stopped and the access visually checked at once. Silencing or widening an alarm hides the very event the alarm exists to catch, and giving saline or medication is outside the technician's scope.
Source: NNCC CCHT content outline, Clinical and Technical practice areas (needle dislodgement and venous pressure alarm response)Report a problem with this question
4. The air detector alarms; the machine has stopped the blood pump and closed the venous line clamp. What is the technician's correct action?
- A.Tape over or disable the detector, since the alarm is usually a false reading
- B.Reset the alarm and continue, documenting it at the end of the treatment
- C.Restart the pump so the air is pushed through the circuit and out of the drip chamber
- D.Keep the venous line clamped and the pump stopped, find and correct the source of the air, and notify the nurse; if air may have reached the patient, position the patient on the left side in Trendelenburg, give oxygen and call for help✓ Answer
The air detector and its line clamp are the last barrier between the circuit and the patient's bloodstream, so the machine's response of stopping the pump and clamping the line must never be overridden or bypassed. Air returned to the venous circulation can lodge in the heart and lungs as an air embolus, and left-side Trendelenburg positioning helps trap air away from the pulmonary outflow while oxygen and immediate nursing help are obtained.
Source: NNCC CCHT content outline, Technical practice area (air detector and venous line clamp)Report a problem with this question
5. A trainee asks what the venous drip chamber is for. Which explanation is correct?
- A.It filters bacteria and endotoxin out of the returning blood
- B.It removes urea and other wastes from the blood before the blood returns
- C.It warms the blood to body temperature on its way back to the patient
- D.It allows air and foam to rise out of the blood before it returns to the patient and provides the connection point where venous pressure is monitored✓ Answer
Solute removal happens only across the dialyzer membrane, not in the drip chamber. The chamber works by slowing the blood in a widened space so that air and foam, being lighter, separate upward and are trapped before the blood reaches the air detector and the patient, and its port is where the pressure transducer, protected by a transducer protector, reads venous pressure.
Source: NNCC CCHT content outline, Technical practice area (extracorporeal circuit components)Report a problem with this question
6. Blood and dialysate are run in opposite directions through the dialyzer. Why is this countercurrent arrangement used?
- A.It maintains a concentration gradient along the entire length of the dialyzer, so diffusion of wastes out of the blood continues from one end to the other✓ Answer
- B.It keeps the dialysate temperature stable across the dialyzer
- C.It allows the machine to remove fluid without a transmembrane pressure
- D.It prevents blood from clotting inside the fibers
Diffusion depends on a difference in concentration across the membrane. If the two fluids flowed in the same direction, the dialysate would quickly load up with solute and the gradient would collapse partway along the fiber; running them in opposite directions means the blood always meets fresher dialysate as it travels, preserving the gradient end to end and increasing clearance.
Source: Standard nephrology reference on hemodialysis principles (countercurrent flow and diffusive clearance)Report a problem with this question
7. A new technician asks where the dialysate used during treatment comes from. Which description is correct?
- A.It arrives from the manufacturer as ready-to-use sterile bags that are hung on the machine
- B.It is simply the reverse osmosis product water, which already contains the needed electrolytes
- C.The machine proportions acid concentrate and bicarbonate concentrate with treated water in a fixed ratio, continuously, as the treatment runs✓ Answer
- D.The two concentrates are first mixed together at full strength and then diluted with tap water
Dialysate is made at the machine, in real time, by diluting an acid concentrate that carries the electrolytes and a bicarbonate concentrate that carries the buffer with water that has already passed the full treatment train. Because the proportioning ratio is built into the machine, the acid and bicarbonate concentrates must be matched to each other and to the machine's setup, and the concentrate in use must be identified on the machine.
Source: ANSI/AAMI standard for concentrates for hemodialysis; NNCC CCHT content outline, Technical practice areaReport a problem with this question
8. Why must the acid concentrate and the bicarbonate concentrate be kept in separate containers and separate machine lines until they are diluted?
- A.Because the bicarbonate concentrate would dissolve the red-labeled acid connector
- B.Because mixing them would neutralize the dextrose in the acid concentrate
- C.Because the acid concentrate must be warmed before the bicarbonate is added
- D.Because at full strength the two react and calcium and magnesium precipitate out as carbonate salts, so the correct electrolyte composition would be lost✓ Answer
Calcium and magnesium carbonate are poorly soluble. At concentrate strength, bringing bicarbonate together with the calcium and magnesium in the acid concentrate drives them out of solution as a precipitate, which both fouls the fluid path and leaves the delivered dialysate short of those cations. Only after each concentrate has been separately diluted with treated water are the ions dilute enough to stay in solution.
Source: ANSI/AAMI standard for concentrates for hemodialysis (separate acid and bicarbonate concentrates)Report a problem with this question
9. A machine alarms for low conductivity partway through a treatment. What is the most common cause a technician should check first?
- A.The dialyzer membrane has ruptured
- B.The patient's blood pressure has dropped
- C.The venous needle has infiltrated
- D.An acid or bicarbonate concentrate container has run empty, or the pickup wand is out of the jug✓ Answer
Conductivity reflects how much dissolved electrolyte the proportioned dialysate contains, so it falls whenever the machine is drawing less concentrate than the ratio requires. Running out of concentrate or a wand sitting outside the container is by far the most frequent reason; wrong concentrate and proportioning pump failure are the next things to consider. The technician corrects the concentrate supply, confirms the reading, and reports the event.
Source: NNCC CCHT content outline, Technical practice area (dialysate conductivity monitoring)Report a problem with this question
10. The dialysate conductivity has fallen below the acceptable range and the machine has gone into bypass. Why would dialyzing on this dialysate be dangerous for the patient?
- A.It would prevent any fluid from being removed during the treatment
- B.The dialysate would be too dilute, or hypotonic, so water would move into the red blood cells and cause hemolysis✓ Answer
- C.It would raise the patient's potassium to dangerous levels
- D.It would make the dialysate hypertonic and cause severe thirst and hypertension
Low conductivity means too little electrolyte for the amount of water, so the dialysate is hypotonic relative to blood. Water then moves osmotically across the membrane into the red blood cells until they swell and burst. High conductivity produces the opposite problem, a hypertonic dialysate with hypernatremia, thirst, headache and hypertension. Either way the machine bypasses and the technician must not run the treatment until the dialysate is back in range.
Source: NNCC CCHT content outline, Technical practice area (dialysate composition and conductivity)Report a problem with this question
11. Before starting the next patient, the technician is checking the dialysate. Which practice is correct?
- A.Adjust the machine's conductivity alarm limits so the reading falls back inside the acceptable window
- B.Begin the treatment and recheck conductivity after the patient is connected
- C.Verify the machine's displayed conductivity and approximate pH with an independent meter, document the results, and report any out-of-range value to the nurse and the person responsible for the equipment✓ Answer
- D.Accept the machine's own displayed conductivity, since the machine self-calibrates at start-up
An independent meter is required precisely because the machine's own sensor is the thing that could be wrong; a self-check cannot detect its own drift. Verification is done and documented before the patient is connected, and correcting or recalibrating the machine or changing alarm limits is the job of a qualified equipment technician, never something done to silence an alarm during or just before a treatment.
Source: NNCC CCHT content outline, Technical practice area (checking conductivity and pH with an independent device)Report a problem with this question
12. A machine has entered bypass because of an out-of-range dialysate reading. What is physically happening?
- A.Fresh dialysate continues through the dialyzer but ultrafiltration is switched off
- B.The dialysate is recirculated back through the dialyzer a second time to correct its composition
- C.The blood pump stops and the venous line is clamped
- D.Dialysate is diverted to the drain and stops flowing through the dialyzer, so out-of-specification dialysate never contacts the blood; blood keeps circulating and heparin keeps infusing, but clearance and fluid removal stop✓ Answer
Bypass is a dialysate-side safety response, triggered by conductivity or temperature outside limits. Diverting the dialysate to drain protects the patient because the only route from dialysate to blood is across the dialyzer membrane, and that route is now empty of dialysate. The blood circuit is untouched, which is why prolonged bypass wastes treatment time and increases clotting risk and must be corrected and reported promptly.
Source: NNCC CCHT content outline, Technical practice area (dialysate bypass function)Report a problem with this question
13. A machine alarms because the dialysate temperature has risen above the set range and the machine has gone into bypass. Why does dialysate temperature matter, and what should the technician do?
- A.The technician should raise the temperature alarm limit so the machine leaves bypass and treatment can proceed
- B.Temperature affects only patient comfort, so the technician may continue the treatment and simply document the alarm
- C.The technician should add cool water to the bicarbonate concentrate to bring the temperature down
- D.Overheated dialysate can damage red blood cells and cause hemolysis, so the treatment stays in bypass or is stopped, the nurse and the person responsible for the equipment are notified, and the machine is taken out of service until repaired✓ Answer
Dialysate is normally delivered near body temperature; blood is separated from it by only a thin membrane, so excess heat is transferred directly to the red cells and can lyse them. Temperature is therefore a hard safety limit that triggers bypass, and the technician's role is to keep the patient protected, escalate to the nurse and equipment personnel, document, and remove the machine from service rather than widen the alarm window.
Source: NNCC CCHT content outline, Technical practice area (dialysate temperature monitoring and bypass)Report a problem with this question
14. With the ultrafiltration goal and rate unchanged, the transmembrane pressure has climbed steadily over the past hour and the dialyzer fibers look dark in places. What does this most likely mean?
- A.The patient has become fluid overloaded
- B.The dialyzer membrane has ruptured
- C.Blood is clotting in the dialyzer, so less membrane surface is available and more pressure is needed to move the same amount of fluid; the technician follows facility protocol for assessing the circuit and notifies the nurse✓ Answer
- D.The dialysate conductivity has fallen
Transmembrane pressure is the driving force for ultrafiltration across the membrane. When fibers clot, the effective surface area shrinks, so the machine must generate more pressure to achieve the ordered fluid removal, and the rising trend is the early warning. A ruptured membrane produces a blood leak alarm instead, and conductivity problems trigger bypass, not a TMP climb.
Source: NNCC CCHT content outline, Technical practice area (transmembrane pressure and dialyzer clotting)Report a problem with this question
15. The blood leak detector alarms during a treatment. What has the detector sensed, and what is the correct response?
- A.It has sensed that the arterial needle has infiltrated; the technician resites the needle
- B.It has sensed blood in the dialysate leaving the dialyzer, indicating a ruptured membrane; the treatment is stopped, the blood in the circuit is not returned to the patient, the nurse is notified, and the dialyzer and lines are replaced✓ Answer
- C.It has sensed air in the venous line; the technician removes the air at the drip chamber and resumes
- D.It has sensed a fall in dialysate conductivity; the technician changes the concentrate container
The blood leak detector is an optical sensor in the dialysate outflow line; it responds to red cells that have crossed a break in the membrane. Because the dialysate side is not sterile, blood that has contacted it must not be given back to the patient, so the circuit is discarded rather than rinsed back, and the nurse is notified for further assessment.
Source: NNCC CCHT content outline, Technical practice area (blood leak detection)Report a problem with this question
16. Which statement correctly describes the role of the water softener in the dialysis water treatment train?
- A.It removes chlorine and chloramine before the water reaches the reverse osmosis membrane
- B.It is the primary purification device and removes the widest range of contaminants
- C.It removes bacteria and endotoxin from the product water
- D.It exchanges calcium and magnesium, the hardness ions, for sodium, which protects the reverse osmosis membrane from scaling✓ Answer
The softener is a pretreatment component whose ion-exchange resin trades hardness ions for sodium. Hardness left in the feed water would deposit as scale on the reverse osmosis membrane and destroy its performance, which is why softening comes before the membrane. Chlorine and chloramine removal is the job of the carbon tanks, bacteria and endotoxin removal is the job of the ultrafilter, and reverse osmosis is the primary purification step.
Source: ANSI/AAMI standard for water treatment equipment for hemodialysis, pretreatment components; CMS ESRD Conditions for Coverage, 42 CFR 494.40Report a problem with this question
17. Why are carbon adsorption tanks a critical part of the water treatment train for dialysis?
- A.They adsorb chlorine and chloramine, which would otherwise cross the dialyzer membrane into the blood and damage red blood cells, causing hemolysis and anemia, and would also destroy the reverse osmosis membrane✓ Answer
- B.They sterilize the water so that no bacteria reach the distribution loop
- C.They add back the electrolytes that reverse osmosis removes
- D.They remove hardness so the reverse osmosis membrane does not scale
Municipal water is disinfected with chlorine or chloramine, and the dialyzer membrane offers no protection against a molecule that small. Once in the bloodstream chloramine is a direct oxidant to red blood cells, producing hemolysis and methemoglobinemia, which is why carbon beds are placed in series before the reverse osmosis unit and why the water is tested for chlorine before patients are treated. Carbon adsorbs chemicals but does not remove hardness or bacteria.
Source: CMS ESRD Conditions for Coverage, 42 CFR 494.40 (carbon adsorption and chlorine/chloramine control)Report a problem with this question
18. Testing at the sample port located between the first and second carbon tanks returns a positive chlorine result before the day's first patient. What should the technician do next?
- A.Immediately test at the sample port after the second (polishing) carbon tank and report the finding; if that port is also positive, patients must not be dialyzed on that water until the problem is corrected✓ Answer
- B.Start the day's treatments, since the second carbon tank will remove whatever the first one missed
- C.Backwash the first carbon tank and record the result as negative
- D.Repeat the same test at the same port later in the day
Carbon beds are installed in series precisely so that a breakthrough at the first bed is caught while the second bed still protects the patients. A positive first-port result is therefore a signal to test the final port immediately, not an assumption that the polisher is working. Only a negative result after the final bed allows treatments to proceed while a replacement bed is arranged, and the technician reports the result to the person responsible for the water system and documents it.
Source: CMS ESRD Conditions for Coverage, 42 CFR 494.40 (carbon bed testing and breakthrough response)Report a problem with this question
19. A facility's water system includes a deionizer after the reverse osmosis unit. Why must an ultrafilter be installed downstream of the deionizer?
- A.Because the ultrafilter is needed to raise the resistivity of the deionized water
- B.Because the ultrafilter removes the chloramine that the deionizer releases
- C.Because the ultrafilter restores the hardness that the deionizer strips out
- D.Because the deionizer removes dissolved ions but no bacteria or endotoxin, and its resin beds can themselves become a site of bacterial growth, so a filter capable of removing bacteria and endotoxin must follow it✓ Answer
Deionization works by ion exchange: cation resin swaps positive ions for hydrogen and anion resin swaps negative ions for hydroxide, which combine as water. Nothing in that process touches microorganisms, and the large wetted resin surface is a favorable environment for bacteria and the endotoxin they shed. The ultrafilter is the polishing component that retains bacteria and endotoxin, though it removes no dissolved chemicals.
Source: ANSI/AAMI standard for water treatment equipment for hemodialysis (deionization and ultrafiltration as polishing components)Report a problem with this question
20. A patient asks why the clinic spends so much effort treating its water when tap water is safe to drink. What is the best explanation for the technician to give?
- A.Treated water tastes better, which helps patients tolerate treatment
- B.Water treatment is required only because the machines would corrode otherwise
- C.Tap water contains too little sodium to make dialysate
- D.During each treatment the patient's blood is exposed to a very large volume of water across a thin membrane, with none of the protection the digestive tract provides, so contaminants that are harmless to drink can pass straight into the bloodstream✓ Answer
Drinking water standards assume a modest daily intake and an intact gastrointestinal barrier that absorbs selectively. In hemodialysis the water used to make dialysate contacts the blood across a membrane in far greater volume and with no such barrier, so trace contaminants are delivered directly and repeatedly. That is the reason the water must pass a defined treatment train and be monitored for chemical and microbiological quality.
Source: CMS ESRD Conditions for Coverage, 42 CFR 494.40 (water and dialysate quality)Report a problem with this question
21. What is the purpose of priming and rinsing a new dialyzer and bloodline set with normal saline before the patient is connected?
- A.To warm the dialyzer to body temperature so the patient does not feel cold
- B.To saturate the membrane with sodium so that dialysate is not needed at the start of treatment
- C.To test the membrane for a leak by pressurizing it
- D.To wet the membrane and displace all air from the blood compartment and the lines, and to rinse out residual sterilant or manufacturing residue so it does not enter the patient✓ Answer
Priming serves two safety purposes at once: it fills the circuit so that air is not carried into the venous line, and it flushes the blood path of anything left from sterilization or manufacture that should never reach the bloodstream. The volume and method are specified by the manufacturer's instructions for use and the facility's procedure, and a reprocessed dialyzer additionally requires a residual germicide test before use.
Source: NNCC CCHT content outline, Technical practice area (dialyzer set-up and priming per manufacturer instructions)Report a problem with this question
22. A facility reprocesses dialyzers. Before connecting a reprocessed dialyzer, what must the technician confirm?
- A.That the dialyzer is labeled with that patient's own name and identifying number and its number of previous uses, that the label is checked against the patient using two identifiers, and that the germicide has been rinsed out and a residual germicide test performed with an acceptable result✓ Answer
- B.Only that the dialyzer is the same model the patient used last time
- C.That the dialyzer has been used fewer times than the dialyzer of the patient in the next chair
- D.That the dialyzer has been rinsed, since the germicide evaporates on its own
A reprocessed dialyzer belongs to one patient and one patient only, so identity verification with two identifiers before every use is what prevents a cross-use event, and facilities must have a procedure for similar-sounding names. Germicide does not disappear on its own; it must be actively rinsed and then proven absent by a residual test, because germicide returned to the bloodstream is harmful. Each reprocessing cycle is documented with the tests performed and the person who performed them.
Source: CMS ESRD Conditions for Coverage, 42 CFR 494.50 (reuse of hemodialyzers); ANSI/AAMI standard for reuse of hemodialyzersReport a problem with this question
Practice questions based on the NNCC CCHT content outline, CDC recommendations for hemodialysis settings, and the OSHA Bloodborne Pathogens Standard. Not affiliated with or endorsed by NNCC, and not medical advice. Machine settings, dialysate composition, flow rates, alarm thresholds, water-quality limits and laboratory targets are deliberately never the answer to a question here — those are set by your machine's manufacturer, your facility's protocol and the physician's prescription. Always follow your facility's policies and your patient's prescribed treatment. About the CCHT exam (NNCC) →