Frequently asked questions in capnography

This section was added because many readers asked the following questions. Clicking on 'detail' sign, will go to the detailed information page. Click the "back button"  to return to this page.

1. How does capnography reflect endobronchial intubation?


2. Is there a relation between cardiac output and PETCO2?


3. What happens to PETCO2 when there is pneumothorax?


4. Does end-tidal PCO2 reflect arterial PCO2 during anesthesia using LMA in healthy subjects?


5. The author is frequently called into operating rooms to determine the cause of abnormal capnogram as shown below?


Air leaks in the sampling tubes can result in capnograms as shown above.

The following capnogram ("tail up" ) can also occur during air leak as a result of accidentally crushed sampling tube.


6. What are the various components of a time capnogram?

A terminology based on logic and convention was suggested several years ago to represent various components of a time capnogram which is now being adapted by several authors. This can be also found in the latest edition of Nunn's Respiratory Physiology.


7. This is another capnogram which may not be an infrequent occurrence.


Can you identify?


8. How does inhalational agents affect carbon dioxide measurements?

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9. What is the relationship between alveolar dead space and (a-ET)PCO2?

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10. How does (a-ET)co2 change on OLV ?

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11. Does end-tidal Pco2 predict Paco2 during laparoscopic surgery?


12. What is arterial to end-tidal Pco2 difference in pregnant subjects undergoing laparoscopic surgery?