Chart — Airway Management
Capnography Waveform Patterns Chart
The shape of the capnogram tells a story the number alone cannot. A square box means a patent airway and steady ventilation; a sloped shark-fin warns of obstruction; a flat line is an emergency. This chart pairs each waveform RTs must recognize with what it means and the action it should prompt.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Capnography Waveforms Side by Side
| Pattern | Appearance | Cause / Action |
|---|---|---|
| Normal | Rectangular waveform; EtCO2 35–45 mmHg | Patent airway with adequate ventilation and perfusion |
| Obstruction / bronchospasm | “Shark-fin” — a sloped, prolonged upstroke with loss of the alveolar plateau | COPD, asthma, or airway obstruction; treat the bronchospasm |
| Esophageal intubation / no ventilation | Flat, absent waveform | The tube is not in the trachea (or apnea, disconnection, or complete obstruction) — confirm and act immediately |
| Hypoventilation | Rising EtCO2, taller boxes | Decreased rate or tidal volume; increase ventilation |
| Hyperventilation | Falling EtCO2, shorter boxes | Increased rate or tidal volume; reduce ventilation |
| Curare cleft | A notch dipping into the plateau | A spontaneous breath during paralysis — neuromuscular blockade is wearing off |
| Sudden loss to zero | The waveform drops abruptly to baseline | Disconnection, tube displacement or extubation, complete obstruction, or cardiac arrest — check the patient and the circuit |
| Rising baseline | The baseline does not return to zero | Rebreathing of CO2 (a faulty valve, an exhausted absorber, or inadequate expiratory time) |
Clinical Notes
- EtCO2 reflects two things. EtCO2 reflects ventilation AND perfusion — a sudden drop can mean a circuit problem OR a fall in cardiac output (cardiac arrest, large PE).
- It confirms the tube. Waveform capnography is the standard for confirming and continuously monitoring ETT placement.
- Read the shape. A sloped shark-fin signals airway obstruction.
Related Resources
Sources
- American Association for Respiratory Care. AARC clinical practice guideline: capnography/capnometry during mechanical ventilation 2011. Respir Care. 2011;56(4):503-509.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.