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