End-Tidal Carbon Dioxide

capnography co2 end tidal carbon dioxide monitoring patient safety Aug 19, 2024

“Probably the most important monitor for patients under anaesthetic.” 😱


End-tidal CO2, also known as capnography, is measured by a tiny tube that carries gas from the patient 🌬️ (connected to the filter near the airway connection) to the machine for analysis 🧑‍🔬.


👉🏻 Why is capnography so important?  

The human body is filled with cells that need to make energy ⚡. To make energy, cells use oxygen and glucose. A byproduct of this process is carbon dioxide (CO2) 😮‍💨. We need to get rid of this CO2 before it becomes harmful. So, the CO2 enters the bloodstream and is carried by the venous system to the lungs 🩸➡️🫁. There, it crosses over into the alveoli and is exhaled 🫁➡️😮‍💨. Too much or too little CO2 in the blood can be harmful, and that’s why we need to set our ventilator settings to eliminate the right amount of CO2 🛠️.


👉🏻 What does it tell us?  

1️⃣ We know that the airway is in the correct position because it’s receiving gas from the lungs. This is super important after the patient has been intubated!


2️⃣ We know the ventilator is working properly and all connections are okay, because we can see that CO2 is travelling from the lungs to the machine, and the waveform indicates the respiratory rate 📈.  


3️⃣ We also know roughly how much CO2 is in the blood 🩸 (because we assume it’s pretty close to what comes from the alveoli).


👉🏻 What is the normal range? ⚖️

The number should be between 35-40 mmHg and the waveform should be square and regular.


👉🏻 What are the sources of error? ⚙️

These are usually equipment issues, such as erroneous calibration, blockage, kinking, or disconnection of the tiny tube. 


Check out Live Series 17 to see capnography in action! 🎥🩺


Build knowledge ✅

Improve safety ✅


Ref: Madden, JD. Monitoring Essentials Summary Document: The Anaesthetic Assistant Starter Course. Periop Concepts - 2022. Available from periopconcepts.com.

 

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