| |
|
|
|
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 |
|
|
|
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.
