21 The Machine & Water Treatment Practice Questions & Answers

1. 1. A technician is preparing the water treatment system before the first patients of the day. Where should the sample for chlorine testing be drawn, and why?

   • A.From the port between the two carbon tanks, because it reveals breakthrough of the first tank while the second still guards.✓ Answer
   • B.From the port after the softener, because chlorine is exchanged onto the resin there along with calcium and magnesium.
   • C.From the port after the reverse osmosis unit, because that membrane is the last barrier standing before water reaches the machines.
   • D.From the port on the city feed line, because the utility sets the disinfectant level that the whole system must handle.

   Carbon beds are installed in series precisely so that exhaustion of the first (worker) tank can be detected while the second (polisher) tank still protects patients. Sampling only at the very end of the train would hide that early warning, and neither the softener nor the reverse osmosis membrane removes chlorine or chloramine.

   Source: ANSI/AAMI standard for hemodialysis water treatment equipment, carbon adsorption bed requirements; CMS ESRD Conditions for Coverage, 42 CFR 494.40Report a problem with this question

2. 2. The chlorine sample drawn between the two carbon tanks exceeds the facility's limit before the first shift. What should the technician do FIRST?

   • A.Rebed both carbon tanks at once and restart the system, since a reading above the limit condemns the whole carbon bank.
   • B.Start the treatments and repeat the test on the same port later in the shift, since the second tank has not been checked yet.
   • C.Switch the loop to the bypass line and run the treatments on softened water that has not yet passed the carbon tanks.
   • D.Draw and test a sample from the port after the second carbon tank to learn whether treated water is still within limit.✓ Answer

   A result above the limit at the intermediate port means the worker tank is exhausted, not that the treated water is unsafe. The required next step is to test immediately after the polisher tank, because that reading decides whether treatment may proceed while the first tank is serviced.

   Source: ANSI/AAMI standard for hemodialysis water treatment equipment, chlorine and chloramine monitoring; CMS ESRD Conditions for Coverage, 42 CFR 494.40Report a problem with this question

3. 3. The sample taken after the second (polisher) carbon tank also exceeds the limit, and patients are waiting to be put on. What is the correct action?

   • A.Reduce the blood flow rate on every machine and begin, because slower flow lowers the chloramine dose each patient receives.
   • B.Install a fresh carbon tank and start the shift meanwhile, because the polisher still removes most of the chloramine present.
   • C.Hold all treatments, notify the nurse in charge and the biomedical staff, and keep the water system out of use.✓ Answer
   • D.Add an extra ultrafilter to each machine and proceed, because those filters trap the oxidant before it reaches the dialyzer.

   When the sample after the polisher tank is also over the limit, the entire carbon bank has failed and the product water may not be used for dialysis; treatments already running must be stopped and none may be started. Ultrafilters remove bacteria and endotoxin but not dissolved oxidants, and lowering blood flow does not make contaminated water safe.

   Source: ANSI/AAMI standard for hemodialysis water quality, chloramine action limits; CMS ESRD Conditions for Coverage, 42 CFR 494.40Report a problem with this question

4. 4. Over two weeks several patients on the same shift show falling hemoglobin and rising erythropoietin requirements, and one reports chest and back pain during the run. Which water problem best explains this pattern?

   • A.Endotoxin passing a torn ultrafilter, which triggers chills and fever during the run and drives the same anemia pattern.
   • B.Aluminum passing a failed reverse osmosis membrane, which binds oxygen on the red cell and causes this same oxidant injury.
   • C.Calcium and magnesium passing a spent softener, which stiffen red cell membranes and shorten their survival in the loop.
   • D.Chloramine passing an exhausted carbon bed, which oxidizes red cells and causes hemolysis that no infection explains.✓ Answer

   Chloramine is an oxidant that attacks the red cell directly, so carbon breakthrough shows up as unexplained hemolytic anemia, resistance to erythropoietin, and chest or back pain in patients sharing the same water. Endotoxin produces fever and chills during the treatment rather than progressive anemia, and aluminum injury presents as bone and neurologic disease.

   Source: ANSI/AAMI standard for hemodialysis water quality, contaminant effects; Core Curriculum for the Dialysis Technician, water treatmentReport a problem with this question

5. 5. A new technician asks why the carbon tanks are plumbed ahead of the reverse osmosis unit rather than after it. What is the best answer?

   • A.Carbon needs the higher line pressure found upstream, because adsorption of dissolved gases only works under that pressure.
   • B.Carbon removes the sand and rust that would score the RO membrane, a job the membrane cannot do to protect itself.
   • C.Carbon adsorbs the chlorine and chloramine that would otherwise damage the RO membrane, which cannot remove them itself.✓ Answer
   • D.Carbon lowers water hardness ahead of the membrane, since scale from calcium is what destroys thin-film membranes fastest.

   Reverse osmosis rejects dissolved ions, bacteria and endotoxin but does not remove chlorine or chloramine, and those oxidants degrade the membrane itself. Placing carbon adsorption upstream both protects the membrane and is the only step in the train that takes the oxidant out of the water.

   Source: ANSI/AAMI standard for hemodialysis water treatment equipment, pretreatment sequenceReport a problem with this question

6. 6. The hardness test on water leaving the softener is suddenly high and the brine tank is empty. What is the consequence if the system keeps running this way?

   • A.Calcium and magnesium are no longer exchanged for sodium, so they scale the RO membrane and burden every later stage.✓ Answer
   • B.Sediment is no longer trapped in the resin bed, so particles reach the carbon and shorten the contact time it provides.
   • C.Bacteria are no longer held on the resin bed, so endotoxin in the product water climbs above the action level.
   • D.Chlorine is no longer exchanged for sodium, so the carbon tanks take the full oxidant load and break through much earlier.

   The softener works by ion exchange, trading calcium and magnesium for sodium, and it needs salt in the brine tank to regenerate that resin. Without regeneration, hardness passes downstream and scales the reverse osmosis membrane, which is the component the softener exists to protect.

   Source: ANSI/AAMI standard for hemodialysis water treatment equipment, softener and pretreatment requirementsReport a problem with this question

7. 7. A facility uses a deionizer to polish the water after reverse osmosis. Why must an ultrafilter be installed downstream of that deionizer?

   • A.The resin bed raises the water temperature as it works, and the filter after it cools the water before the storage tank.
   • B.The resin bed removes ions but grows bacteria and releases endotoxin, so a filter after it protects the product water.✓ Answer
   • C.The resin bed releases carbon fines as it works, and the filter after it keeps those particles out of the storage tank.
   • D.The resin bed removes bacteria but not ions, so the filter after it is what finally lowers the conductivity of the water.

   Deionization removes charged particles only; the warm, wet resin bed is an excellent site for bacterial growth and the endotoxin those organisms release passes straight downstream. An ultrafilter after the deionizer, together with continuous resistivity monitoring, is therefore required to keep the product water microbiologically acceptable.

   Source: ANSI/AAMI standard for hemodialysis water treatment equipment, deionization requirementsReport a problem with this question

8. 8. The machine display shows conductivity and temperature inside the set range and no alarms are active. What must the technician still do before the patient is connected?

   • A.Ask a second technician to read the same machine display and initial the treatment record beside the machine's value.
   • B.Watch the machine display through a full rinse cycle and write down the lowest reading seen during that observation.
   • C.Measure the dialysate with a separate calibrated meter and record the reading beside the value the machine displays.✓ Answer
   • D.Confirm in the manufacturer's service log that the machine's internal cell was calibrated during the last service visit.

   The machine's own cell can drift or fail, so its display cannot verify itself; an independent, calibrated meter is required to confirm the dialysate before the patient is connected, and both values are documented. A second person reading the same suspect display adds nothing, because it is the instrument and not the observer that is being checked.

   Source: ANSI/AAMI standard for hemodialysis systems, independent verification of dialysate; CMS ESRD Conditions for Coverage, 42 CFR 494.40Report a problem with this question

9. 9. The independent meter reading for conductivity does not agree with the machine's display, although both values fall inside the facility's acceptable range. What should the technician do?

   • A.Take the machine out of service, tag it, notify biomedical staff, and move the patient to a machine that verifies correctly.✓ Answer
   • B.Reduce the dialysate flow rate until the two readings match, then begin and re-check the pair midway through the run.
   • C.Record both readings on the treatment sheet and start, since each value sits inside the acceptable range for dialysate.
   • D.Re-zero the independent meter and use the machine reading, since the machine's cell is calibrated more often than the meter.

   The point of independent verification is that the machine's display must be validated by an outside measurement; when the two disagree, the machine cannot be trusted to control proportioning even if the numbers look acceptable. The safe response is to remove and tag the machine, report it to biomedical staff, and dialyze the patient on equipment that verifies.

   Source: ANSI/AAMI standard for hemodialysis systems, independent verification of dialysate; CMS ESRD Conditions for Coverage, 42 CFR 494.40Report a problem with this question

10. 10. A conductivity alarm shows a value well below the set range. Compared with correctly proportioned dialysate, what would this fluid do to the patient's blood?

    • A.It is hypotonic, so sodium moves rapidly into the blood and produces cramping with a rise in the patient's blood pressure.
    • B.It is hypotonic, so water moves into the red cells and they swell and burst, which can be fatal within minutes.✓ Answer
    • C.It is hypertonic, so water leaves the red cells and they shrink, producing thirst, headache and a rising blood pressure.
    • D.It is hypertonic, so potassium is driven into the cells and the patient develops weakness and a slowed heart rhythm.

    Conductivity is a surrogate for the total ion content of the dialysate, so a low value means the fluid is too dilute, that is hypotonic to blood. Water then moves osmotically into the red cells until they lyse, which is why low conductivity is the more rapidly lethal direction and why the machine must stay in bypass until the cause is found.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel, dialysate composition and delivery systemsReport a problem with this question

11. 11. When a conductivity or temperature alarm sounds, the machine goes into bypass. What does bypass physically do?

    • A.It routes the dialysate once more through the heater, so the machine can correct the reading without interrupting the run.
    • B.It stops the blood pump and clamps the venous line, so no more blood leaves the patient until the fault is corrected.
    • C.It closes the ultrafiltration controller only, so fluid removal stops while dialysate keeps flowing through the dialyzer.
    • D.It diverts dialysate to the drain instead of through the dialyzer, so the unsafe fluid never meets the patient's blood.✓ Answer

    Bypass is a protective dialysate-side action: the fluid that failed its conductivity or temperature check is routed to drain instead of through the dialyzer, so it never contacts blood across the membrane. Dialysis effectively stops during bypass, which is why the cause must be corrected rather than the bypass defeated.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel, delivery system safety monitorsReport a problem with this question

12. 12. The dialysate temperature reading is climbing above the upper limit and the machine has alarmed. What is the danger if dialysate that is too hot reaches the dialyzer?

    • A.Heat raises the conductivity of the dialysate, so the patient receives a sodium load and becomes thirsty and hypertensive.
    • B.Heat thickens the blood inside the fibers and the dialyzer clots, so the treatment must be restarted with a new circuit.
    • C.Heat drives dissolved gas out of the dialysate and that air crosses the membrane into the blood on the patient's side.
    • D.Heat damages the red cells and they hemolyze, releasing potassium and turning the venous blood dark and cola colored.✓ Answer

    Red cells are heat labile, and dialysate warmer than the safe window destroys them across the membrane, causing acute hemolysis with potassium release, dark venous blood, back and chest pain and possible cardiac arrest. That is why the high temperature limit forces the machine into bypass before the fluid can reach the dialyzer.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel, dialysate temperature controlReport a problem with this question

13. 13. A new technician asks why the acid concentrate and the bicarbonate concentrate are never combined in one container before they reach the machine. What is the reason?

    • A.Undiluted, they neutralize each other and the mixture loses all of the potassium the prescription calls for that day.
    • B.Undiluted, they raise the sodium of the mixture so far that no proportioning ratio can bring it back into the range.
    • C.Undiluted, they react and precipitate calcium and magnesium carbonate while releasing carbon dioxide from the solution.✓ Answer
    • D.Undiluted, they foam so heavily that the proportioning pumps draw air and the machine cannot hold its conductivity.

    The acid concentrate carries the calcium and magnesium; brought together with bicarbonate at full strength, those cations form insoluble carbonates and carbon dioxide comes out of solution. The machine avoids this by proportioning each concentrate separately into a large stream of treated water, where the dilution keeps the salts in solution.

    Source: ANSI/AAMI standard for concentrates for hemodialysis, bicarbonate and acid concentrate handlingReport a problem with this question

14. 14. Before a treatment the extracorporeal circuit is primed and rinsed with normal saline. What is the main purpose of this step?

    • A.To displace all air from the dialyzer and the lines and rinse the dialyzer as the manufacturer's instructions direct.✓ Answer
    • B.To coat the fibers with saline protein so that heparin can be reduced for patients at risk of bleeding that day.
    • C.To warm the dialyzer fibers so that blood entering them does not cool and clot during the first minutes of the run.
    • D.To test the venous pressure alarm limits, since saline flowing through the circuit reproduces the pressures of blood.

    Priming fills the circuit with saline so that no air remains to be pumped toward the patient, and the rinse removes manufacturing residues and any storage or germicide solution from the dialyzer. Saline contains no protein, so it cannot coat fibers or substitute for anticoagulation.

    Source: Core Curriculum for the Dialysis Technician, extracorporeal circuit setup and primingReport a problem with this question

15. 15. Ten minutes into treatment the pre-pump arterial pressure becomes steadily more negative and the line pulls flat with each pump stroke. What should the technician do FIRST?

    • A.Raise the blood pump speed to pull past the obstruction and then watch whether the arterial pressure moves back toward zero.
    • B.Move the arterial pressure limits wider so the alarm clears, then finish the run and report the reading at the end.
    • C.Lower the blood pump speed and inspect the arterial needle and line for kinking or a needle lying against the wall.✓ Answer
    • D.Give a saline bolus into the venous line and increase the ultrafiltration rate to compensate for the volume given.

    An increasingly negative pre-pump pressure means the pump is demanding more blood than the inflow can deliver, from a kink, a clamp, a needle against the vessel wall, or an access that cannot supply the set rate. Reducing pump speed relieves the suction while the inflow is inspected; raising the speed increases the negative pressure and can damage the access and the red cells.

    Source: Core Curriculum for the Dialysis Technician, extracorporeal pressure monitoring and troubleshootingReport a problem with this question

16. 16. Two hours into a treatment the venous pressure has risen steadily although the blood pump speed has not been changed, and the venous drip chamber looks dark. What is the most likely cause?

    • A.A separation at the venous needle connection, which lets blood escape and lowers the resistance the pump must meet.
    • B.Clot forming in the venous drip chamber and in the dialyzer, which narrows the path the blood takes back to the patient.✓ Answer
    • C.Air entering ahead of the pump, which compresses in the chamber and cushions the pressure the monitor can sense.
    • D.Hypotension in the patient, which reduces the volume the access can deliver and lowers pressure across the circuit.

    Venous pressure reflects resistance between the dialyzer and the patient, so a steady rise at an unchanged pump speed means that path is narrowing, most often from clot in the drip chamber, the dialyzer or the venous needle. Line separation and hypotension both reduce resistance and would move the venous pressure down instead of up.

    Source: Core Curriculum for the Dialysis Technician, venous pressure monitoring and circuit clottingReport a problem with this question

17. 17. The venous pressure falls abruptly toward zero and the alarm sounds while the blood pump keeps turning. What should the technician do FIRST?

    • A.Add saline to the venous drip chamber until the level rises, then reset the alarm and continue the treatment as ordered.
    • B.Lower the venous pressure alarm floor so the machine will run, then examine the drip chamber level at the next check.
    • C.Raise the blood pump speed so the venous pressure climbs back inside the limits, then look for the cause of the drop.
    • D.Stop the blood pump, clamp the lines, and check the venous needle and every connection for separation from the patient.✓ Answer

    A sudden loss of venous pressure means the circuit has lost resistance, and the most dangerous explanation is a disconnected line or a dislodged venous needle pumping blood onto the floor or the bed. The protective action comes first: stop the pump and clamp, then inspect the access and connections and call the nurse before restarting anything.

    Source: Core Curriculum for the Dialysis Technician, venous pressure alarms and needle dislodgementReport a problem with this question

18. 18. The air detector alarms, the blood pump stops and the venous line clamp closes. What is the correct response?

    • A.Restart the pump at the slowest speed so any bubbles present will dissolve before the blood returns to the patient.
    • B.Override the detector so the pump restarts, then watch the drip chamber closely for the rest of the treatment time.
    • C.Keep the pump stopped and the line clamped, find where air entered, clear the circuit and have the nurse assess the patient.✓ Answer
    • D.Tap the sensor housing until the alarm clears, since a low chamber level rather than real air usually triggers it.

    The detector and clamp are the last barrier between an air embolus and the patient's circulation, so the machine's stop must be respected until the source is identified and the air removed. Overriding the monitor, tapping the sensor or restarting slowly all allow air to be pumped into the venous return, and any suspicion that air reached the patient requires immediate nursing assessment.

    Source: Core Curriculum for the Dialysis Technician, air detection and safety monitorsReport a problem with this question

19. 19. A blood leak alarm sounds and a test of the dialysate outflow is positive for blood. What is the correct action?

    • A.End the treatment and discard the blood in the circuit rather than returning it through the damaged dialyzer.✓ Answer
    • B.Return the blood to the patient with saline, then replace the dialyzer and finish the remaining time on the run.
    • C.Silence the alarm and lower the transmembrane pressure, since a small leak usually seals as the fibers rewet.
    • D.Rinse the dialysate side clear with fresh dialysate and continue, since the detector reads bubbles as false blood.

    A confirmed blood leak means the membrane is ruptured and the blood in the circuit has been exposed to non-sterile dialysate, so it must not be rinsed back into the patient. The treatment is terminated, the circuit discarded, the nurse and biomedical staff notified and the event documented; only a negative confirmatory test points to a false alarm from bubbles or a soiled sensor.

    Source: Core Curriculum for the Dialysis Technician, blood leak detection and responseReport a problem with this question

20. 20. Midway through a treatment the transmembrane pressure climbs steadily although the ultrafiltration goal and the pump speed are unchanged, and streaks of the dialyzer are darkening. What does this indicate?

    • A.Fibers are clotting, so the surface left for fluid removal shrinks and the machine needs more pressure to meet the same goal.✓ Answer
    • B.The heparin dose is too high, so blood thins and crosses the membrane more easily, lifting the reading.
    • C.Dialysate flow has stopped, so the pressure on that side falls away and the reading drifts up without any clotting.
    • D.Fibers are wetting fully at last, so the membrane passes fluid more freely and the reading rises with the better flow.

    Transmembrane pressure is the driving pressure the machine must generate to pull the ordered volume of fluid across the membrane. As fibers clot, effective membrane surface falls, so the same ultrafiltration goal demands progressively higher pressure; the darkening streaks confirm the clotting, and the nurse should be notified so anticoagulation and the circuit can be evaluated.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel, transmembrane pressure and dialyzer clottingReport a problem with this question

21. 21. A facility that reprocesses dialyzers hands the technician one for the next patient. What must be confirmed before it is connected?

    • A.That the label carries this patient's own name and number and that the rinsed dialyzer tests free of residual germicide.✓ Answer
    • B.That the fiber bundle volume is unchanged from new and that it has been used fewer times than the patient's last one.
    • C.That the housing carries no cracks and that the dialyzer has been stored in the clinic for at least one full day.
    • D.That the ports were capped with fresh caps and that the dialyzer was rinsed with the same water used to mix concentrate.

    A reprocessed dialyzer belongs to one patient only, so identity must be verified against the label before it is used, and the germicide used for storage must be rinsed out and shown absent by test, because residual disinfectant entering the blood causes hemolysis and can be fatal. Fiber bundle volume is checked during reprocessing but does not stay identical to new, and a dialyzer that fails any of these checks is discarded.

    Source: ANSI/AAMI standard for reprocessing of hemodialyzers, residual germicide testing and patient identificationReport 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) →