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Designed, Produced, and maintained (Edition 12, 2022) by 

Bhavani Shankar Kodali MD

Updated September 2022

Analysis of CO2 waveforms:

Clinical Aspects

Bhavani Shankar Kodali MD

    Analysis of CO2 waveforms:

Elevated inspiratory base line:            

An elevated inspiratory base line and phase I indicates CO2 rebreathing, which is abnormal with circle breathing systems, and suggests either an exhausted C02 absorbent in circle system or incompetent valves.1-6 It is normally anticipated with the Bain anaesthetic system using controlled ventilation.4,7  A sudden elevation in both the base line and the PETCO2 usuallly indicates contamination of the sample cell with water, mucus or dirt, whereas a gradual rise suggests rebreathing.8 

 Normal  Rebreathing -Exhausted soda line - Elevation of the base line

Rebreathing as a result of soda lime exhaustion -Trend and wave capnograms showing gradual elevation of the base line
 Trend  Waveform

 Contamination of CO2 monitor (sudden elevation of base line and top line)  Contamination of CO2 monitor - trend
 Clinicalapplication /Clinicalapplication/Images/contaminationtrend.gif

 Inspiratory valve malfunction - Elevation of the base line, prolongation of down stroke, prolongation of phase III

 Capnogram during the use of Bain anesthetic circuit. Inspiratory base line and phase I are elevated above the zero due to rebreathing. Note the rebreathing wave during inspiration.  Inspiration =           


1.    Pyles ST, Berman LS, Modell JH.  Expiratory valve dysfunction in a semiclosed circle anesthesia circuits - verification by analysis of carbon dioxide waveforms.  Anesth Analg 1984;63:536-7.

2.    Berman LS, Pyles ST.  Capnographic detection of anaesthesia circle valve malfunctions. Can J Anaesh 1988;35:473-5.

3.    Van Ganderingen HR, Gravenstein N, Van der Aa JJ, Gravenstein JS.  Computer-assisted capnogram analysis.  J Clin Monit 1987;3:194-200.

4.    Weingarten M. Respiratory monitoring of carbon dioxide and oxygen:  a ten-year perspective. J Clin Monit 1990;6:217-25.

5.    Kumar AY, Bhavani-Shankar K, Moseley HSL, Delph Y.  Inspiratory valve malfunction in a circle system: Pitfalls in capnography.  Can J Anaesth 1992;39:997-9.

6.    Bhavani-Shankar K, Moseley H, Kumar AY, Delph Y. Anaesthesia and capnometry. (Review article).  Can J Anaesth 1992;39:617-32.

7.    Adams AP. Capnography and pulse oximetery. In: Atkins RS, Adams AP (Eds.). Recent Advances in Anaesthesia and Analgesia.  London: Churchill Livingston, 1989;155-75.

8.    Sweadlow DB, Irving SM.  Monitoring and patient safety.  In: Blitt CD (Ed.). Monitoring in Anesthesia and Critical Care Medicine. 2nd ed., New York: Churchill Livingstone, 1990;33:64.

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