The Level 2 method for pumps: codes, event history, the analyser and six suspects

Collect the error code, the event history and the clinical story, reproduce the fault on an analyser, place it in the disposable, the mechanism, the sensors, power, electronics or software, and know what you may change at your level and when a pump must not be touched at all.

Where Level 1 stops

In Infusion and Syringe Pump Service — Level 1 you learned how volumetric, syringe and PCA pumps move fluid, how they harm patients, how to test flow, occlusion, air and alarms with an analyser, how to look after batteries and PM, and how to start fault-finding with the disposable and the story. That first round solves most calls: the wrong syringe was selected, the set was from another supplier, the battery was tired, glucose had dried in the door. Level 2 begins with the calls that survive it. The pump alarms 'occlusion' with an approved, freshly primed syringe. It under-delivers by a steady few percent on the analyser. It shows an error number at power-up and nothing else. It worked for a year and now stops every few hours with an internal fault.

At this level you work through suspects in a fixed order, use the pump's own memory, choose tests that separate two suspects, and stop at the boundary your authorisation and the manufacturer's documentation set. The general method is in the Fault-Finding Method for Medical Equipment course; this lesson applies it to pumps.

Six suspects, always in the same order

Split every pump fault into six places. The disposable and the use: syringe brand and size, set type, priming, clamps, filters, extension lines, how it was loaded and selected. The mechanism: fingers and cam or cassette actuator on a volumetric pump; lead screw, half-nut, carriage and plunger clamp on a syringe pump; motor, gearbox and the rotation sensor that confirms movement. The sensors: pressure and occlusion sensing, air-in-line, door and clamp switches, syringe size and plunger detection, drop sensors. Power: mains supply, battery pack and its management electronics, charger, docking station or rack. Electronics: main board, keypad and its ribbon cable, display, speaker, nurse call. Software and data: firmware, configuration, drug library, clock, network module and server.

The order matters because the cost and likelihood of each suspect fall roughly in that sequence. A new approved syringe costs nothing to try. A mechanism inspection costs an hour. A board costs money, and a firmware problem costs the manufacturer's time. If you skip to the board because the code mentions a 'motor' or a 'sensor', you will often be wrong: the motor error may come from a carriage blocked by dried drug, and the sensor error from a syringe the pump was never validated with.

Error codes point to a group, not to a part

Pumps report faults as numbered errors or short messages, and every manufacturer documents them in its own way. In operator manuals the codes are usually grouped by what the user should do: correct the loading, change the syringe, recharge, call service. In service documentation they are grouped by the detecting function: drive monitoring, pressure channel, air channel, power supervision, memory check, communication between processors. Either way a code tells you which check failed, not which component broke. A drive-monitoring error says the commanded and the measured movement disagreed. The cause can be the motor, the gearbox, the rotation sensor, the cable, the board that compares them, or simply a mechanism that is jammed.

Two more things limit what a code tells you. First, the same number can be produced by quite different events. The field cases in this lesson show one family of compact syringe pumps that showed the same power-up error in one case because the battery had been pulled out while the pump was running, and in another because the keypad ribbon cable had broken. Second, some codes are written by the pump after an abnormal shutdown, a watchdog reset or a failed self-check at power-up, and say more about how the pump was handled than about what is broken. Read the code, then read the history around it, then decide.

• Write the code exactly as shown, with the software version and serial number.
• Look it up in the manufacturer's documentation for that model and version only.
• Note the functional group: drive, pressure, air, power, memory, communication, keypad.
• Ask what the pump was doing just before: starting, running, power change, door opened.
• Do not order a part on the code alone.

The event history is your witness

Most current pumps keep an event history with time stamps: power on and off, battery and mains changes, programming steps, starts and stops, rate changes, alarms and acknowledgements, door and syringe events, technical errors. Some keep a separate technical log that only the manufacturer's service software can read. Before you power-cycle, change the battery, update software or run a calibration, save whatever the pump remembers by the method its documentation describes, because some of these actions overwrite or shorten the record. Check the pump clock against real time and note the difference; a history with the wrong time cannot be matched to the nursing record.

Read the history for sequence, not for single lines. A downstream occlusion alarm a few seconds after start, every time, on the same syringe size, is a friction or force-sensing story. An internal error that always follows a mains-to-battery change is a power story. Repeated door-open events during an infusion with nobody touching the pump point at the door switch or its magnet. An internal error once a month at random times, on one pump of thirty, is the hardest kind and needs patience: log every occurrence and what changed.

Reproduce on the analyser before you open anything

Set the pump up on the bench the way it was used: same syringe brand and size or the same set, same rate, same occlusion level, same power source. Use a new approved disposable from stock as the reference, then the ward's disposable from the same batch if you have it. Connect the analyser and run long enough to see the behaviour; low-rate faults take time to show. If the fault appears with the approved disposable, the pump is the suspect. If it appears only with the ward's disposable, you have found the cause outside the pump, and the fix is a conversation with the ward and the supply department, not a repair.

Change one thing at a time and write each result down: approved syringe against the ward's syringe; mains against battery; this pump against a known-good pump of the same model with the same disposable. A known-good pump is the cheapest test instrument you have. Results from an analyser that is out of calibration, or from a test line set up differently from the manufacturer's procedure, are useful for your own reasoning but are not evidence for release.

What you may change, and what you may not

Within your authorisation and the manufacturer's documentation you may replace user-replaceable and field-replaceable parts, clean and inspect the mechanism, set configuration values the clinical owner has agreed, load software the manufacturer released for that pump, and run the manufacturer's performance verification and calibration procedures if you have been trained on them and have the specified tools. You may not enter service functions with codes obtained outside the manufacturer's channel, reset a service interval counter without the planned maintenance it reminds you of, raise an occlusion limit to stop alarms caused by a disposable, calibrate the pump to a syringe that is not on its list, fit parts that are not specified for the pump, or bypass a door, clamp or air detector. If the fix needs a step you are not authorised for, your result is a clear report of what you tested and excluded.

When the pump must not be touched

One situation overrides the whole method. If the pump may have been involved in harm to a patient, or in a near miss such as a free flow, an overdose or an alarm that did not sound, it is evidence before it is a repair job. Level 1 lesson 6 described sequestration; at Level 2 the risk is that you are the one who destroys the evidence, because you are the person most likely to switch it on, pull the battery or download the log the wrong way. Keep it as found, with the disposable, the remaining fluid, the container and the labels. Do not clean, power-cycle, test, update or repair it unless the hospital's incident procedure, the manufacturer or the regulator tells you how. Lesson 7 covers what happens next.

On-site checklist

• Ask first whether the pump could have been involved in patient harm.
• Save code, history, clock offset, software version and serial number before any reset.
• Reproduce with a new approved disposable at the ward's rate and occlusion level.
• Compare with a known-good pump of the same model and the same disposable.
• Test on mains and on battery separately.
• Change one thing at a time and record every result.
• Stop at your authorisation boundary and report what you excluded.

Check yourself