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What This Guide Helps With
Troubleshooting low exhaled volume alarms caused by circuit leaks, disconnections, obstructions, accessories, alarm settings, reduced test-lung volume, or expiratory measurement problems.
Step-by-Step Troubleshooting
1. Ensure Patient Safety First
Do not troubleshoot a low exhaled tidal volume or low minute volume alarm while the Puritan Bennett 980 is actively supporting a patient.
- Notify respiratory therapy and the clinical team immediately.
- Transfer the patient to another verified ventilator or approved ventilation method.
- Confirm adequate ventilation, oxygenation, and alarm operation on the replacement device.
- Do not assume the alarm is caused by equipment failure; it may reflect a real change in the patient’s ventilation.
Expected outcome: The patient is safely supported without relying on the affected ventilator.
Continue Clinical Engineering troubleshooting only after the PB980 has been removed from patient use.
2. Identify the Exact Alarm
Review the active alarm banner and alarm log. Determine whether the PB980 reports:
- Low exhaled mandatory tidal volume
- Low exhaled spontaneous tidal volume
- Low exhaled total minute volume
- Circuit disconnect
- Apnea
- High circuit pressure
- Severe occlusion
- Another simultaneous technical or gas-delivery alarm
The PB980 activates the low exhaled tidal-volume alarms when measured mandatory or spontaneous exhaled volume is at or below its corresponding alarm limit. The low exhaled total minute-volume alarm occurs when measured mandatory and spontaneous minute volume is at or below the configured limit.
Expected outcome: The exact alarm type and any associated alarms are documented.
If the alarm occurred because the displayed exhaled volume legitimately fell below an appropriately configured limit, stop and return the clinical assessment to respiratory therapy.
3. Review Alarm Limits and Ventilator Settings
With the ventilator connected to an approved test lung, verify:
- Patient category and predicted body weight
- Ventilation mode
- Set tidal volume or pressure
- Mandatory respiratory rate
- Pressure support
- Inspiratory time
- PEEP
- Low mandatory tidal-volume limit
- Low spontaneous tidal-volume limit
- Low total minute-volume limit
Do not change alarm limits solely to silence the alarm. Compare the settings with the reported clinical configuration or facility-approved test setup.
Expected outcome: The alarm limit is appropriate for the intended test conditions and is not inadvertently set above the expected exhaled volume.
If correcting an incorrectly entered setting resolves the alarm and the ventilator passes functional testing, stop.
4. Inspect the Complete Patient Circuit
Examine the inspiratory and expiratory limbs from the ventilator to the patient connection.
Look for:
- Loose or partially seated connections
- Disconnected tubing
- Split, punctured, or stretched tubing
- Loose elbows, adapters, or Y-pieces
- Open sampling or accessory ports
- Missing port caps
- Incorrect circuit assembly
- Water accumulation
- Kinked or compressed tubing
Reconnect or replace suspect components using compatible parts.
Expected outcome: The circuit is fully connected, correctly assembled, unobstructed, and free of visible leaks.
If replacing or reseating the circuit resolves the alarm, complete operational testing and stop.
5. Inspect the Test Lung or External Load
Confirm that the test lung:
- Is connected securely
- Is not torn or leaking
- Has appropriate compliance and resistance
- Produces repeatable expansion and recoil
- Is suitable for the selected adult, pediatric, or neonatal circuit category
Substitute a known-good test lung when available.
Expected outcome: The ventilator delivers repeatable breaths and the exhaled volume remains above the configured alarm limits.
If the alarm disappears with the known-good test lung, the original test lung or external load was the cause. Stop.
6. Check the Exhalation Filter and Condensate Collection Components
Inspect the exhalation filter, condensate vial, filter adapter, and nearby connections.
Verify that:
- The exhalation filter is the correct type.
- The filter is fully seated.
- The condensate vial is installed and secured.
- The filter is not visibly wet, contaminated, damaged, or occluded.
- Seals and mating surfaces are clean and undamaged.
- No gas is escaping around the filter or collection assembly.
Replace a wet, damaged, contaminated, or suspect filter with an approved compatible filter.
Expected outcome: Exhaled gas flows through a properly installed and unobstructed exhalation assembly without leakage.
If filter replacement resolves the alarm, perform functional verification and stop.
7. Inspect Humidification and Added Accessories
Check any humidifier, nebulizer, suction adapter, flow sensor, sampling line, closed-suction system, or specialty connector installed in the circuit.
Look for:
- Loose accessory connections
- Open access ports
- Incorrectly installed adapters
- Cracked components
- Excess condensate
- Increased resistance
- Accessory configurations that were not included during circuit setup
Temporarily remove nonessential accessories and test using a basic approved circuit and test lung.
Expected outcome: The alarm clears when a leaking, obstructed, or incorrectly installed accessory is removed or replaced.
If the basic circuit operates normally, identify and replace the defective accessory before returning the ventilator to service.
8. Compare Inspired and Exhaled Volume Measurements
Observe the displayed inspired tidal volume, exhaled tidal volume, total respiratory rate, minute volume, airway pressure, and leak information.
Determine whether:
- Inspired volume is also lower than expected.
- Inspired volume appears normal but exhaled volume is substantially lower.
- Airway pressure reaches the expected level.
- Delivered volume changes from breath to breath.
- A significant leak is indicated.
- The alarm occurs only during mandatory or spontaneous breaths.
The manufacturer identifies leaks and obstructions as possible causes of low exhaled mandatory tidal volume. During pressure-based ventilation, changes in resistance or compliance can also reduce measured tidal volume even when the selected pressure is achieved.
Expected outcome: The pattern indicates whether the issue is associated with delivery, leakage, obstruction, settings, or exhaled-volume measurement.
9. Check for Circuit Obstruction or Excessive Resistance
Inspect for resistance caused by:
- Kinked tubing
- Occluded filters
- Water-filled circuit sections
- Blocked adapters
- Restricted test-lung connections
- Incorrectly sized circuit components
- Closed or partially closed accessory valves
Replace suspect components rather than attempting to clean or modify disposable circuit parts.
Expected outcome: Airflow is unrestricted and delivered and exhaled volumes remain stable.
If removing the obstruction resolves the alarm, complete operational testing and stop.
10. Perform a New Circuit Test When Appropriate
After replacing the circuit, filter, humidification components, or major accessories, perform the manufacturer-defined circuit test or system check required for that configuration.
Use:
- The correct patient category
- The complete circuit configuration intended for testing
- Approved filters and accessories
- Required gas supplies
- Stable AC power
Do not perform the test with a patient attached.
Expected outcome: The circuit test completes successfully without leaks, compliance errors, or resistance-related failures.
If the circuit test fails repeatedly with a known-good circuit, remove the ventilator from service.
11. Test With a Known-Good Circuit Configuration
Install a known-good:
- Patient circuit
- Exhalation filter
- Condensate vial
- Test lung
- Humidification configuration, when required
Repeat ventilation using controlled, documented settings.
Expected outcome: Exhaled tidal volume and minute volume remain stable and above their alarm limits.
If the ventilator works with the known-good configuration, replace the defective external component and document the finding.
12. Evaluate for an Expiratory Measurement or Internal Flow-System Problem
Suspect an internal problem when:
- The alarm persists with a verified circuit and test lung.
- Inspired volume appears appropriate but exhaled volume remains implausibly low.
- Exhaled readings are erratic or inconsistent.
- Multiple known-good filters and circuits produce the same result.
- Circuit testing repeatedly fails.
- Technical alarms accompany the volume alarm.
- The exhalation valve flow sensor or internal pneumatic system appears unable to measure flow correctly.
Do not disassemble the breath-delivery unit, exhalation module, flow sensors, or internal pneumatic components unless trained, authorized, and following the applicable service documentation.
Expected outcome: External causes have been ruled out and the unit is identified for formal bench evaluation.
If the Problem Persists
If the alarm continues after verifying settings, circuit integrity, filters, accessories, test lung, and circuit-test results, the problem is likely associated with the exhalation flow-measurement system, internal pneumatic components, calibration, or ventilator electronics.
The ventilator should be:
- Removed from service
- Labeled Out of Service
- Sent for qualified bench evaluation or authorized repair
- Subjected to all required performance and alarm testing before clinical return
The PB980 operator’s manual includes low exhaled mandatory tidal volume, low spontaneous tidal volume, and low total minute volume among the alarms evaluated during formal alarm testing.
Knowing when to stop external troubleshooting is proper Clinical Engineering practice.
Clinical Use Tip
Never dismiss a low exhaled volume alarm as a faulty ventilator until the patient has been clinically assessed. Reduced tidal or minute volume may reflect disconnection, leakage, obstruction, altered lung mechanics, apnea, or reduced respiratory effort.
Move the patient to another verified ventilator before Clinical Engineering testing whenever dependable ventilation cannot be assured.
Work Order Documentation (CCR Method)
CCR = Complaint, Cause, Resolution
Complaint
What was reported by the clinical staff.
Example:
"Respiratory therapy reported repeated low exhaled tidal volume and low total minute volume alarms during operation of the Puritan Bennett 980."
Cause
What was observed during troubleshooting.
Example:
"Inspection found a loose connection at the exhalation filter assembly that allowed circuit leakage and reduced measured exhaled volume."
Resolution
What action was taken.
Example:
"Reseated the exhalation assembly, replaced the filter, completed the circuit test, and verified stable tidal and minute-volume measurements using a test lung."
Helpful Details to Include (If Known)
- Exact alarm message and priority
- Mandatory, spontaneous, or total minute-volume alarm
- Ventilation mode and patient category
- Set and measured tidal volume
- Set and measured respiratory rate
- Measured minute volume
- Low-volume alarm limits
- Inspired-versus-exhaled volume comparison
- Leak value or leak behavior
- Circuit and filter condition
- Condensate present
- Accessories installed
- Test lung used
- Circuit test result
- Associated alarms
- Power behavior
- Environmental factors
- Indicator lights
- Final device status
Final Thought
Low exhaled volume alarms require both clinical caution and logical equipment troubleshooting. Protect the patient first, verify settings and external breathing-circuit components, reproduce the issue safely, and escalate when measurements remain unreliable. Clear CCR documentation supports safe return to service and future repair decisions.
That is successful troubleshooting.