Waveform Capnography in ACLS: What End-Tidal CO2 Tells You

Waveform capnography is the most useful monitor in a cardiac arrest after the ECG. The ACLS course teaches four uses for it.

1. Airway confirmation

A consistent waveform confirms that an advanced airway is in the trachea, and continuous monitoring shows immediately if it becomes displaced. See airway management.

2. CPR quality

End-tidal CO2 during CPR reflects blood flow through the lungs. A persistently low reading — the course uses a figure below 10 mmHg — suggests compressions need to be improved: check depth, rate, recoil and fatigue, and swap compressors. See compression rate and depth.

3. Detecting ROSC

An abrupt, sustained increase in end-tidal CO2 often means circulation has returned, sometimes before a pulse is felt. Check for a pulse at the next rhythm check and prepare for post-arrest care.

4. Guiding ventilation

After ROSC, capnography helps the team ventilate to normal CO2 and avoid hyperventilation.

Pitfalls

• Adrenaline can transiently lower end-tidal CO2.
• A leak, disconnection or blocked tube changes the trace.
• Trends matter more than a single number.

Capnography appears throughout the arrest pathways and is a common topic in ACLS practice questions.

This guide summarises what the ACLS course teaches for education only. It is not a clinical protocol: follow the current American Heart Association guidelines, linked below, and your institution’s policies.

More ACLS guides: ACLS algorithms and skills

• ACLS Course in Abu Dhabi — dates, format and booking
• ACLS Algorithms Explained: Cardiac Arrest, Bradycardia, Tachycardia and Post-Arrest Care
• The ACLS Systematic Approach: BLS, Primary and Secondary Assessment
• ACLS Cardiac Arrest: VF and Pulseless VT (the Shockable Pathway)
• ACLS Asystole and PEA: The Non-Shockable Pathway
• ACLS Bradycardia Algorithm: Atropine, Pacing and Infusions
• ACLS Tachycardia Algorithm: Stable vs Unstable Tachycardia
• ACLS Post-Cardiac Arrest Care: What Happens After ROSC
• The H's and T's of ACLS: Reversible Causes of Cardiac Arrest
• ACLS Drugs: Adrenaline, Amiodarone, Atropine, Adenosine and More
• ACLS Rhythms: The ECG Rhythms You Need to Recognise
• ACLS Airway Management: From Bag-Mask to Advanced Airway
• Acute Coronary Syndromes in ACLS: Recognition and First Steps
• Acute Stroke in ACLS: Recognition, Timing and First Steps
• ACLS Megacode: How It Works and How to Pass as Team Leader
• ACLS Electrical Therapy: Defibrillation, Cardioversion and Pacing
• All ACLS guides, by topic

Other life support and first aid courses: BLS Course · PALS Course · First Aid Course · Training calendar

Frequently asked questions

What does a low end-tidal CO2 during CPR mean?

That CPR quality may need improving.

How does capnography show ROSC?

An abrupt, sustained increase in end-tidal CO2.

Why use capnography with an advanced airway?

To confirm placement and detect displacement.

Does adrenaline affect end-tidal CO2?

It can cause a transient decrease.

Is capnography taught in ACLS?

Yes, as part of the arrest and airway cases.

Sources and further reading

What we teach follows the awarding body and the UAE health authorities. For the definitive position on a course or licensing question, these are the places to check.

• CPR and ECC Guidelines — American Heart Association
• Advanced Cardiovascular Life Support (ACLS) — American Heart Association

Last reviewed 21 September 2026 by the training team at Safety First Medical Services, an American Heart Association training centre at Addax Office Tower, Al Reem Island, Abu Dhabi. Call +971 55 761 9841 or email training@safetyfirstmed.ae.