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What This Guide Helps With
Troubleshooting missing CO₂ waveform, unstable capnogram, or inaccurate EtCO₂ readings caused by setup, sampling, patient connection, or module issues.
Step-by-Step Troubleshooting
Ensure Patient Safety First
If the Philips NM3 is actively monitoring a patient, verify that clinical staff are aware of the missing or questionable CO₂ reading.
If EtCO₂ monitoring is clinically required, move the patient to another working capnography monitor or approved monitoring method before troubleshooting.
Expected outcome: Patient ventilation monitoring continues safely.
If this resolves the immediate patient safety concern, continue troubleshooting only when safe.
Verify the Reported Problem
Confirm whether the issue is:
- No CO₂ waveform
- Flat waveform
- Intermittent waveform
- EtCO₂ value missing
- EtCO₂ value present but inaccurate
- Delayed response
- Frequent occlusion, sampling, or calibration-related messages
Expected outcome: The exact symptom is confirmed before parts are replaced or the device is removed from service.
Check the Patient and Airway Connection
Confirm the sampling line, airway adapter, cannula, or nasal/oral sampling device is properly connected to the patient circuit or patient interface.
Look for disconnection, loose fittings, reversed adapters, or sampling ports not exposed to exhaled gas.
Expected outcome: CO₂ waveform appears and EtCO₂ value returns to expected monitoring behavior.
If corrected, document the connection issue and stop.
Inspect the CO₂ Sampling Line or Adapter
Check the sampling line for:
- Kinks
- Crushed tubing
- Moisture
- Secretions
- Blood
- Condensation
- Blockage
- Loose luer connection
- Incorrect accessory type
Replace the sampling line or airway adapter with a known-good compatible accessory.
Expected outcome: A blocked or defective sampling accessory is ruled out or corrected.
If the waveform returns after replacing the accessory, stop troubleshooting.
Confirm the Correct Accessory Is Being Used
Verify that the accessory is appropriate for the Philips NM3 and the type of monitoring being performed.
Confirm the setup matches the clinical application, such as intubated, non-intubated, sidestream, or sampling-line monitoring.
Expected outcome: The monitor receives a valid respiratory gas sample.
Why it matters: Incorrect or incompatible accessories can cause weak waveforms, inaccurate EtCO₂ readings, or no breath detection.
Check for Moisture or Contamination at the Module Connection
Inspect the module’s sampling inlet and the sampling line connector area for visible fluid, contamination, or damaged fittings.
Do not force tubing into a damaged port. Do not attempt deep internal cleaning.
Expected outcome: External contamination or connection damage is identified.
If fluid contamination is suspected inside the module, remove the device or module from service.
Verify Monitor and Module Recognition
Confirm the Philips monitor recognizes the NM3 module and displays CO₂ parameters.
Check for module-related messages, missing parameter boxes, communication errors, or startup failures.
Remove and reseat the module only if safe and appropriate for the setup.
Expected outcome: The monitor recognizes the module and CO₂ monitoring becomes available.
If the module is not recognized after reseating, remove it from service for evaluation.
Check Alarm, Scale, and Display Settings
Confirm CO₂ monitoring is enabled and that the waveform is not hidden, minimized, or scaled in a way that makes it appear flat.
Review EtCO₂ alarm limits, waveform display settings, and parameter configuration.
Expected outcome: A display or configuration issue is ruled out.
If the waveform was hidden or misconfigured, correct the setting, verify operation, and stop.
Compare Against a Known-Good Setup
If available, test the same patient setup with a known-good CO₂ module, sampling line, or monitor.
Alternatively, test the NM3 module on a compatible known-good monitor if allowed by site practice.
Expected outcome: The issue follows either the accessory, patient setup, monitor, or NM3 module.
Why it matters: Swapping known-good external components helps avoid unnecessary module replacement.
Check for Patient or Clinical Factors
If the waveform exists but the EtCO₂ value appears low, high, or inconsistent, confirm clinical staff have evaluated the patient and ventilation status.
Possible non-equipment causes may include shallow breathing, poor sampling position, mouth breathing with nasal cannula, leak around the airway connection, low tidal volume, or ventilation changes.
Expected outcome: Equipment troubleshooting does not override clinical assessment.
Perform a Functional Check Off Patient
Using site-approved test equipment, simulator, or known-good CO₂ source, verify whether the NM3 can detect CO₂ and display a stable waveform/value.
Do not use the device for patient care if the reading cannot be verified.
Expected outcome: CO₂ function is confirmed or the fault is reproduced off patient.
Review Recent Service, Cleaning, or Damage History
Check whether the module was recently dropped, cleaned, exposed to fluid, moved between monitors, or returned from a clinical area with accessory contamination.
Expected outcome: Recent handling or environmental exposure is considered before declaring a random failure.
If the Problem Persists
If the Philips NM3 still has no CO₂ waveform, inaccurate EtCO₂ readings, intermittent detection, module recognition problems, or suspected contamination after external checks, common external causes have been ruled out.
The device or module should be:
- Removed from service
- Labeled Out of Service
- Sent for repair, calibration verification, or bench evaluation according to site policy
Do not continue patient use with unreliable CO₂ monitoring. Knowing when to stop is proper troubleshooting.
Clinical Use Tip
Do not troubleshoot a questionable CO₂ reading on an active patient unless clinical staff have confirmed the patient is safe and alternate monitoring is available.
A missing or inaccurate EtCO₂ value can hide a real ventilation problem.
Move the patient to a backup device or approved monitoring method first so therapy and ventilation monitoring continue safely.
Work Order Documentation (CCR Method)
CCR = Complaint, Cause, Resolution
Complaint
What was reported by the clinical staff.
Example:
"Clinical staff reported no CO₂ waveform and no reliable EtCO₂ reading from the Philips NM3 during patient monitoring."
Cause
What was observed during troubleshooting.
Example:
"Found the CO₂ sampling line kinked near the patient connection, preventing proper gas sampling."
Resolution
What action was taken.
Example:
"Replaced the sampling line, verified waveform and EtCO₂ returned, and confirmed the monitor operated normally before returning to service."
Helpful Details to Include (If Known)
- Whether patient was moved to another monitor
- Exact symptom: no waveform, flat waveform, unstable waveform, or inaccurate value
- Sampling line type used
- Sampling line replaced
- Airway adapter or cannula checked
- Moisture, secretions, or blockage found
- Module reseated
- Monitor recognized the NM3 module
- Alarm or display settings checked
- Known-good accessory or module swapped
- Any error or status message displayed
- Final device status
Final Thought
For CO₂ waveform and EtCO₂ issues, start with patient safety and the sampling path before assuming module failure. Most field troubleshooting should focus on connections, accessories, moisture, settings, and comparison testing. If the reading cannot be trusted after those checks, remove the device from service and document the work clearly.
That is successful troubleshooting.