Capnography Waveform

What Is Capnography Waveform?

The capnography waveform is the graph plotted by a capnometer showing exhaled CO2 concentration against time, and its shape — not just the ETCO2 number — carries diagnostic information. A normal waveform has a rectangular shape: a flat baseline during inspiration, a rapid upstroke as exhalation begins, an alveolar plateau as CO2-rich air from the alveoli is exhaled, and a sharp downstroke as the next inspiration begins. Deviations from this shape point to specific problems: a rising baseline suggests rebreathing or exhausted CO2 absorbent, a curved 'shark fin' shape with a sloped upstroke indicates bronchospasm (classic in asthma or COPD exacerbations), a sudden drop to zero suggests a dislodged airway or disconnected circuit, and an irregular or absent plateau can indicate an air leak around the airway device.

Why Capnography Waveform Matters on the Fireground

Reading the waveform shape, not just glancing at the ETCO2 number, lets EMS providers catch problems in real time — recognizing a shark-fin pattern early allows for immediate bronchodilator treatment adjustment, while recognizing a sudden flatline can mean the difference between quickly identifying a dislodged airway and continuing to ventilate a patient whose airway has actually failed. Learning to interpret waveform morphology, not just trend the number, is what separates basic capnography use from proficient capnography use in the field.

Relevant NFPA Standards

• AHA Guidelines: Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
• NFPA 455: Standard for Emergency Medical Services (EMS)

Field Procedures & Tactical Steps

1. Confirm a normal rectangular waveform with a clear alveolar plateau immediately after connecting the capnography sensor.
2. Watch for a sloped, shark-fin-shaped waveform, which suggests bronchospasm and may prompt earlier or repeated bronchodilator treatment.
3. Investigate immediately if the waveform suddenly flattens or disappears, checking for airway dislodgement, circuit disconnection, or loss of perfusion.
4. Note a rising baseline that never returns to zero, which can indicate rebreathing or exhausted CO2 absorbent material in certain ventilation setups.
5. Document significant waveform changes and correlate them with the patient's clinical presentation and treatment response.

Common Context & Application

Interpreted continuously on any patient connected to a capnography monitor, particularly useful in distinguishing bronchospasm from other causes of respiratory distress, confirming airway integrity after placement or movement, and catching circuit disconnections or rebreathing during ventilation.

Frequently Asked Questions about Capnography Waveform