Capnography in Children
What is Capnography?
Capnography is a monitoring method that measures the amount of carbon dioxide (CO2) in a person's exhaled breath in real time. Every time a person breathes out, CO2 is released from the lungs. Capnography captures and displays this information, usually as a number and a wave pattern on a screen.
The key value it measures is called End-Tidal CO2 (ETCO2) - the highest amount of CO2 present at the very end of a breath out. In healthy individuals, this value is typically between 35 and 45 mmHg (or 4.5-6% CO2).
Capnography gives instant, continuous feedback about how well the lungs and breathing are working - without needing a blood test.
Key Term - ETCO2
End-Tidal CO2 (ETCO2) is the concentration of carbon dioxide measured at the end of a complete breath out. It reflects how well the body is breathing, circulating blood, and removing CO2.
Purpose of Capnography - Why It Is Used
Capnography serves several critical purposes in healthcare settings. It provides continuous, real-time data about a patient's breathing and circulatory status.
Primary Uses
- Confirm correct tube placement: After a breathing tube (endotracheal tube) is inserted into the airway, capnography immediately confirms whether it is correctly placed in the windpipe (trachea) and not the food pipe (esophagus). This is one of its most critical functions.
- Monitor breathing during sedation and anesthesia: During procedures where sedative medications or general anesthesia are used, breathing can become slow or stop. Capnography gives instant warning before blood oxygen levels even begin to drop.
- CPR monitoring: During cardiopulmonary resuscitation (CPR), ETCO2 values show how effective the chest compressions are. A rising ETCO2 is a sign of returning circulation.
- Assess respiratory conditions: Conditions like asthma, bronchiolitis, or severe breathing problems change the shape of the CO2 waveform. Capnography helps monitor severity and response to treatment.
- Emergency and critical care: Used in emergency rooms, intensive care units (ICUs), and during patient transport to continuously monitor breathing status.
- Procedural sedation: During painful procedures such as fracture reduction, burn wound care, or lumbar punctures where sedation is used.
Where Capnography Is Used
| Setting | Use |
|---|---|
| Operating Room | Continuous monitoring during anesthesia |
| Emergency Department | Tube placement confirmation, CPR, sedation |
| Pediatric ICU (PICU) | Ongoing ventilator and breathing monitoring |
| Pre-hospital / Ambulance | Field monitoring during resuscitation and transport |
| Procedure Rooms | Sedation monitoring during painful procedures |
| Recovery Room (PACU) | Post-anesthesia breathing monitoring |
| General Wards (selected cases) | High-risk patients on opioids or with respiratory illness |
Types of Capnography
There are two main types of capnography, based on where the CO2 sample is measured:
1. Mainstream Capnography
The sensor is placed directly in the breathing circuit - right at the airway. CO2 is measured as it passes through the sensor in real time.
- Faster response time
- No risk of sample line blockage
- Heavier sensor - can place more weight on the breathing tube
- Mostly used in intubated (tubed) patients
2. Sidestream Capnography
A small tube (sample line) continuously draws a sample of exhaled gas from the airway to the monitor for analysis. The sensor is inside the monitor, not at the airway.
- Lighter at the patient's airway
- Can be used in non-intubated patients (through a nasal cannula or mask)
- Sample line can get blocked by secretions or moisture
- Very commonly used in pediatric patients
Microstream Technology
Many modern sidestream capnographs use Microstream technology - a variation that uses a very low gas sampling rate (50 mL/min). This is especially useful in small children and newborns where sampling large volumes of breath is not ideal.
By Patient Type - Intubated vs. Non-Intubated
| Type | Patient Condition | Interface Used |
|---|---|---|
| Intubated Capnography | Patient has a breathing tube | Inline adapter on breathing circuit |
| Non-Intubated Capnography | Patient is breathing on their own | Nasal cannula with CO2 port or face mask |
Understanding the Capnogram - The Wave Display
A capnogram is the waveform (wave-shaped graph) shown on the monitor. It represents CO2 levels across the breathing cycle. Understanding the shape of this wave is important for clinical assessment.
Normal Capnogram - Four Phases
| Phase | What Happens | On Graph |
|---|---|---|
| Phase I | Beginning of breath out - dead space air (no CO2) | Flat baseline near zero |
| Phase II | Mix of dead space and alveolar air - CO2 rises | Sharp upstroke |
| Phase III | Alveolar plateau - mostly CO2-rich air | Near-flat plateau |
| Phase 0 (Inspiration) | Fresh air breathed in, CO2 drops to zero | Sharp downstroke back to baseline |
A normal capnogram has a rectangular shape with a clear plateau. Any change from this shape - such as a sloped plateau, shark-fin appearance, or irregular wave - gives important clinical information about the patient's lung condition.
What Abnormal Waveforms Can Mean
| Waveform Pattern | Possible Cause |
|---|---|
| Shark-fin shape (sloped plateau) | Airway obstruction - asthma, bronchospasm, COPD |
| Elevated ETCO2 (above 45 mmHg) | Hypoventilation, CO2 retention |
| Low ETCO2 (below 35 mmHg) | Hyperventilation, poor perfusion, pulmonary embolism |
| Zero reading | Breathing stopped, tube disconnection, equipment failure |
| Irregular baseline | Cardiogenic oscillations, secretions in airway |
| Double-humped plateau | Cardiac oscillations or non-uniform lung emptying |
How to Use a Capnography Device - Step by Step
Important Note
Capnography is used in clinical settings by trained healthcare personnel. This section describes the process for informational understanding.
Equipment Needed
- Capnograph monitor (standalone or integrated into multiparameter monitor)
- CO2 sensor or sample line (appropriate for patient type - intubated or non-intubated)
- Age-appropriate nasal cannula with CO2 sampling port (for non-intubated) or inline adapter (for intubated)
- Power supply and patient cable
For a Non-Intubated Patient (Sidestream via Nasal Cannula)
1
Turn on the monitor
and allow it to perform self-check and warm-up (usually 30-60 seconds). Check that the CO2 module is calibrated or auto-zeroed as per manufacturer instructions.
2
Attach the sample line
to the capnography port on the monitor. Ensure the connection is secure.
3
Select the correct cannula size
for the patient (neonatal, infant, pediatric, or adult). Place the nasal prongs gently into both nostrils. The CO2 sampling port should face the nostril opening.
4
Secure the cannula
over the ears and adjust under the chin so it stays in place without discomfort.
5
Observe the waveform
on screen. Within a few breaths, a regular capnogram should appear along with the ETCO2 number. If there is no waveform, check for sample line kinks, blockage, or incorrect placement.
6
Set alarm limits
as appropriate. Common default alarms are triggered if ETCO2 drops below 30 mmHg or rises above 50 mmHg, or if no breath is detected within a set time (apnea alarm).
7
Monitor continuously.
Watch the waveform shape, ETCO2 value, and respiratory rate displayed. Document readings as required.
8
Replace sample line
as per institutional protocol (usually every 24 hours or when clogged).
For an Intubated Patient (Mainstream or Sidestream)
1
Turn on the monitor
and allow warm-up and calibration.
2
For mainstream:
Attach the CO2 sensor directly between the endotracheal tube (ETT) and the ventilator circuit Y-piece. Ensure it is not inverted.
For sidestream: Insert the sampling adapter between the ETT and circuit, then connect the sample line to the monitor.
For sidestream: Insert the sampling adapter between the ETT and circuit, then connect the sample line to the monitor.
3
Observe for a waveform.
Correct ETT placement in the trachea shows a consistent capnogram waveform. Absence of waveform after intubation is a strong indicator of esophageal intubation and requires immediate action.
4
Set and confirm alarms.
Monitor continuously during the entire procedure or ventilation period.
5
For mainstream sensors:
Wipe the sensor window if readings become erratic. Moisture or secretions can interfere with the infrared beam.
Normal Values and What They Mean
| Parameter | Normal Range | Notes |
|---|---|---|
| ETCO2 | 35 - 45 mmHg | 4.5-6% CO2; varies slightly with age and condition |
| Respiratory Rate (via capnography) | Age-dependent in children | Newborns: 30-60/min; Infants: 25-40/min; Older children: 18-30/min |
| PaCO2 - ETCO2 gradient | 2-5 mmHg | ETCO2 is usually slightly lower than arterial CO2 (PaCO2) |
In healthy individuals, ETCO2 closely reflects the actual CO2 in arterial blood (PaCO2). A larger gap between the two values suggests poor lung perfusion or lung disease.
Precautions and Potential Risks
Device-Related Precautions
- Sample line blockage: In sidestream capnography, the thin sample tube can get blocked by water droplets or mucus. This gives no reading or falsely low values. Use water trap connectors and check the line regularly.
- Leaks in the circuit: Any air leak around the breathing tube or mask reduces CO2 sampling and gives falsely low readings.
- Mouth breathing: If a nasal cannula is used and the patient breathes through the mouth, ETCO2 readings will be unreliable. Some masks sample both nasal and oral airflow.
- Mainstream sensor weight: In very small infants, the weight of a mainstream sensor on the breathing circuit can put mechanical stress on the breathing tube. Support it with circuit holders.
- Interference from high oxygen flow: High-flow oxygen through a nasal cannula can dilute the exhaled CO2 sample in sidestream capnography, giving falsely lower values.
Alarm Fatigue Warning
Frequent false alarms due to patient movement, crying, or loose connections can cause alarm fatigue - where alarms are ignored. Always investigate every alarm rather than silencing without checking the patient.
Clinical Precautions
- Capnography is a monitoring tool, not a diagnostic device on its own. All values must be interpreted along with clinical assessment.
- In patients with severe lung disease, ETCO2 may not accurately reflect actual blood CO2. Arterial blood gas (ABG) testing provides the most accurate measurement in such cases.
- Never delay resuscitation to set up capnography. Use it as soon as available, but clinical priorities come first.
- The device does not replace clinical observation of chest rise, breath sounds, and patient response.
Signs That Need Immediate Attention
Flat capnogram (no waveform) in an intubated patient, sudden drop of ETCO2 to zero, apnea alarm, sustained ETCO2 above 60 mmHg or below 25 mmHg - all of these require immediate clinical evaluation and action.
Special Considerations in Children
Children have unique physiological characteristics that affect capnography monitoring:
- Higher respiratory rates: Fast breathing in infants can cause waveform overlap or incomplete exhalation, leading to lower-than-actual ETCO2 readings. Capnographs with fast response times are better suited for infants.
- Smaller tidal volumes: Infants breathe smaller volumes. Mainstream sensors can add dead space to the circuit, which is less desirable in very small children. Microstream sidestream systems are preferred.
- Age-appropriate accessories: Use only cannulas, adapters, and sensors designed for the patient's age and size. Using an adult accessory on a small child gives unreliable readings.
- Cooperation: Young children may pull off nasal cannulas. Gentle fixation and distraction techniques help maintain consistent monitoring.
Capnography During CPR
During cardiopulmonary resuscitation, capnography provides important real-time feedback:
- An ETCO2 value above 10 mmHg during CPR suggests that compressions are generating blood flow to the lungs.
- A sudden rise in ETCO2 to normal levels (35-45 mmHg) often signals return of spontaneous circulation (ROSC) - the heart has started beating again.
- A persistently very low ETCO2 (below 10 mmHg) despite good CPR technique may indicate a poor prognosis and is used as one factor in resuscitation decisions.
Capnography is now recommended as a standard monitoring tool during advanced life support (ALS) by major international resuscitation councils including the American Heart Association (AHA) and European Resuscitation Council (ERC).
How to Keep the Device Safe and Well-Maintained
Cleaning and Disinfection
- Always follow the specific manufacturer's cleaning instructions for the capnograph monitor and sensors.
- The external monitor surface can usually be wiped with hospital-grade disinfectant wipes. Avoid spraying liquids directly on the device.
- Mainstream sensors should be cleaned between patients according to the manufacturer's protocol. Some are single-use, others can be disinfected. Never immerse sensors in liquid unless specifically stated as safe to do so.
- Sidestream sample lines, nasal cannulas, and airway adapters are single-use disposable items. They should not be cleaned and reused between patients.
Storage and Handling
- Store the monitor in a clean, dry environment. Avoid extreme temperatures and humidity.
- Keep cables coiled without tight bends to prevent wire damage inside.
- Inspect the sensor window regularly. A dirty or scratched window on a mainstream sensor reduces accuracy.
- Perform daily functional checks - turn the device on, confirm calibration, and test alarms.
- Follow a scheduled preventive maintenance program as set by biomedical engineering or the manufacturer's recommendations.
Calibration
- Many modern capnographs perform automatic self-calibration (auto-zero) when turned on or at set intervals.
- For devices requiring manual calibration, use certified calibration gas with a known CO2 concentration.
- Do not use a device that shows calibration errors or consistent inaccurate readings. Report to biomedical engineering.
Troubleshooting Common Issues
| Problem | Likely Cause | Action |
|---|---|---|
| No waveform | Disconnected sample line, apnea, or tube misplacement | Check connections, check patient |
| Low ETCO2 reading | Sample line leak, high O2 flow dilution, hyperventilation | Check circuit, adjust O2 delivery method |
| Erratic waveform | Moisture in sample line, patient movement | Clear water trap, check cannula position |
| "Check sensor" error | Dirty or damaged sensor | Clean sensor window or replace sensor |
| Alarm not sounding | Alarm muted or volume too low | Check alarm settings and volume |
Capnography vs. Pulse Oximetry - Key Differences
Both are important monitoring tools, but they measure different things:
| Feature | Capnography | Pulse Oximetry (SpO2) |
|---|---|---|
| What it measures | CO2 in exhaled breath | Oxygen saturation in blood |
| Detects breathing problems | Immediately (breath by breath) | With a delay (after desaturation begins) |
| Shows respiratory rate | Yes, directly | Indirectly (some devices) |
| Works without a pulse | Yes (during CPR) | No (needs pulse) |
| Affected by nail polish | No | Yes (dark nail polish) |
Capnography detects breathing problems much earlier than pulse oximetry. When breathing stops or slows, CO2 changes are seen within seconds on the capnogram, while oxygen saturation may take minutes to fall. This early warning is especially important during sedation.
Frequently Asked Questions
Is capnography painful or uncomfortable?
No. For non-intubated patients, only a small nasal cannula is placed. For intubated patients, the sensor attaches to existing tubing. There is no needle or invasive component in capnography monitoring itself.
Can capnography be used in newborns?
Yes. Microstream sidestream capnography is commonly used in neonates. Very small, age-specific accessories are needed. Mainstream sensors are generally avoided in very small infants because of added dead space and weight on the airway.
What does a flat capnogram after intubation mean?
A flat line (no CO2 detected) after placing a breathing tube strongly suggests the tube is in the esophagus, not the trachea. This is a medical emergency and the tube must be repositioned immediately.
Is capnography better than a pulse oximeter?
They measure different things and are both valuable. Capnography shows breathing problems earlier, especially during sedation. Pulse oximetry shows how well oxygen is being delivered to the body. Ideally, both are used together for comprehensive monitoring.
What is a normal ETCO2 in children?
Generally 35-45 mmHg. Values slightly lower (30-35 mmHg) can be seen in normal, healthy children who breathe a little faster. Values below 30 mmHg or above 50 mmHg require clinical evaluation.
Can capnography replace blood gas testing?
No. Capnography provides continuous non-invasive trend monitoring, but it cannot fully replace arterial blood gas (ABG) testing. In patients with lung disease or when precise CO2 values are needed, ABG remains the gold standard. Capnography is used alongside, not instead of, blood gas analysis.
Why does the ETCO2 reading become zero suddenly?
Sudden zero ETCO2 in a monitored patient can mean breathing has stopped (apnea), the breathing tube has come out, the sample line has disconnected or blocked, or the patient has been disconnected from the monitor. Always check the patient immediately when ETCO2 drops to zero.
Is capnography used outside the hospital?
Yes. Portable capnographs are used by paramedics and emergency medical teams in ambulances and on scene. They are especially useful during emergency intubations and CPR in the pre-hospital setting.
How long can capnography monitoring be continued?
Capnography can be used for as long as monitoring is clinically needed - from a short procedural sedation of 20 minutes to days of continuous monitoring in an ICU. Replace sample lines and disposable accessories as per protocol during prolonged monitoring.
Does crying or talking affect capnography readings?
Yes. In non-intubated patients using a nasal cannula, crying, talking, or mouth breathing can cause irregular or intermittent waveforms. The readings may be less reliable during these moments. This is a known limitation of nasal sidestream capnography.
Suggested References and Resources
The following are reliable sources for further reading on capnography in pediatric and clinical practice:
- Books: Fleisher and Ludwig's Textbook of Pediatric Emergency Medicine; Smith's Anesthesia for Infants and Children; Miller's Anesthesia; Tintinalli's Emergency Medicine
- Websites: American Heart Association (heart.org); European Resuscitation Council (erc.edu); American Society of Anesthesiologists (asahq.org); UpToDate (uptodate.com); World Federation of Societies of Anaesthesiologists (wfsahq.org)
- Guidelines: ETCO2 monitoring guidelines from the Joint Commission and national anesthesia and emergency medicine societies are available through their official websites.
Medical Disclaimer
The information provided on this page is intended for general educational and informational purposes only. It is not a substitute for professional medical advice, clinical training, diagnosis, or treatment. Capnography is a medical monitoring device and must only be used by trained and qualified healthcare professionals in appropriate clinical settings. All clinical decisions should be based on full patient assessment by a licensed healthcare provider, institutional protocols, and manufacturer guidelines. PediaDevices does not endorse any specific brand, product, or manufacturer. Medical practices, guidelines, and device specifications may vary by country, institution, and patient condition. Always refer to your local protocols and current clinical guidelines.
Content reviewed and verified by a qualified Pediatrician. | PediaDevices
Labels: Monitoring-Devices