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

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

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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 =

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.

Clinical Aspects

Analysis of CO2 waveforms:

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