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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
 
Clinicalapplication
 
Clinicalapplication

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

 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
 
/Clinicalapplication/Images/valvedefect.gif

 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 =           
 /Clinicalapplication/Images/bain.gif

References:


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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