Smiths Medical Medfusion 3500

Pressure Reading Inaccurate or Occlusion Threshold Behaves Incorrectly

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Asset Type

Infusion Pump

Manufacturer

Smiths Medical

Model

Medfusion 3500

What This Guide Helps With

Troubleshoots pressure or occlusion behavior affected by tubing restrictions, syringe loading, settings, accessories, positioning, or performance problems.

Step-by-Step Troubleshooting

1. Protect the Patient and Maintain Therapy

If pressure monitoring or occlusion detection cannot be trusted, do not continue patient therapy on the affected pump. Transfer the infusion to another verified device when clinically necessary.

Expected outcome: The patient is not dependent on unreliable pressure or occlusion detection.

2. Confirm the Reported Condition

Determine whether staff observed an unexpected occlusion alarm, delayed alarm, pressure value that appeared unreasonable, failure to respond to a restriction, or inconsistent behavior between similar setups.

Expected outcome: The specific pressure-related complaint is clearly defined.

3. Inspect the Complete Fluid Path

Check tubing, clamps, stopcocks, valves, filters, connectors, catheters used in the reported setup when available, and other accessories for partial or complete restriction, kinks, closed pathways, or compression.

Expected outcome: The external test fluid path is patent and correctly configured.

4. Verify Syringe Installation

Confirm the syringe is compatible, undamaged, and properly seated. Check that the plunger moves normally and that the pump's drive maintains appropriate contact without binding or slipping.

Expected outcome: Syringe loading does not create abnormal mechanical resistance.

5. Review Pressure or Occlusion Settings

Verify the clinically intended pressure or occlusion configuration visible through normal operator controls. Compare with the reported setup if known. Do not enter unauthorized service menus or alter protected configuration solely to eliminate an alarm.

Expected outcome: The pump is operating with the intended accessible configuration.

6. Remove Restrictive Accessories for Comparison

On the bench, simplify the setup using known-good compatible tubing and accessories to determine whether the pressure behavior follows a filter, extension, stopcock, valve, or other external component.

Expected outcome: Normal behavior with the simplified setup identifies the original fluid path as the likely cause.

7. Test With a Known-Good Syringe and Tubing Setup

Repeat evaluation using a known-good syringe and uncomplicated test line. Observe whether pressure behavior stabilizes.

Expected outcome: The pump responds consistently with the known-good setup. If so, troubleshooting can stop after documenting and verifying the external cause.

8. Inspect Accessible Mechanical Interfaces

Inspect external syringe and drive-contact areas for residue, debris, damage, or misalignment that could affect force transmission. Do not disassemble the drive or pressure-sensing mechanism.

Expected outcome: Accessible areas are clean, intact, and properly aligned.

9. Perform Approved Performance Testing

Using an appropriate infusion-pump analyzer or other approved test equipment, evaluate pressure or occlusion performance according to applicable manufacturer procedures. Do not invent acceptance limits; use the current approved criteria.

Expected outcome: The device meets the applicable manufacturer-defined test requirements.

10. Escalate Failed or Unstable Performance

If pressure behavior remains inconsistent or the pump fails an approved performance test despite a known-good setup, remove the device from service.

Expected outcome: A pump with questionable occlusion protection is sent for qualified repair or evaluation.

If the Problem Persists

External restrictions, syringe loading, accessories, accessible settings, and setup conditions have been ruled out. Remaining possibilities include calibration, force or pressure sensing, mechanical alignment, configuration, or other service-level faults.

The device should be:

Following corrective action, complete the specified pressure, occlusion, delivery, alarm, and safety tests required for return to service. Stopping after a failed safety-related performance test is proper troubleshooting.

Clinical Use Tip

An infusion pump with unreliable occlusion detection should not be used for therapy even when it appears to deliver normally under no-load conditions.

Work Order Documentation (CCR Method)

CCR = Complaint, Cause, Resolution

Complaint

What was reported by the clinical staff.

Example:
"Nursing reported that the Medfusion 3500 produced repeated occlusion alarms during an otherwise routine infusion."

Cause

What was observed during troubleshooting.

Example:
"Clinical Engineering found a kinked extension line creating excessive downstream resistance; the pump passed bench pressure testing with a known-good setup."

Resolution

What action was taken.

Example:
"The external tubing problem was identified, pump pressure and alarm performance were verified with approved test equipment, and the unit was returned to service."

Helpful Details to Include (If Known)

Final Thought

Pressure complaints often originate in the syringe or fluid path, so verify those first. If approved performance testing remains abnormal, remove the pump from service and document the escalation clearly.

That is successful troubleshooting.

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