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Clinical Aspects Bhavani Shankar Kodali MD |
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Analysis
of CO2 waveforms:
Descending limb:
The descending limb can be prolonged or slanted, when the inspiratory valve of a closed circuit system is incompetent.1-3 or because of the use of side-stream sensor capnographs, with a prolonged response time.4 The capnograph with a prolonged response time also results in the prolongation of phase II and is observed commonly in children.4,5
Ripple effect: At slow
respiratory rates it is common to see a ripple effect, referred to as
cardiogenic oscillations, superimposed on the expiratory plateau and the
descending limb of the capnogram. This arises from small gas movements created
largely by the pulsations of the aorta and heart.6-8
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Inspiratory valve malfunction resulting in prolongation of descending inspiratory limb in addition to prolongation of alveolar plateau |
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Normal |
Prolonged inspiratory descending limb due to dispersion gases in the sampling line or as well as prolonged response time of the analyzer. Seen in children who have faster respiratory rates. |
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Cardiogenic oscillations. Ripple effect, superimposed on the plateau and the descending limb, resulting from small gas movements produced by pulsations of the aorta and heart. |
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1. Berman LS, Pyles ST. Capnographic detection of anaesthesia circle valve malfunctions. Can J Anaesh 1988;35:473-5.
2. Van Ganderingen HR, Gravenstein N, Van der Aa JJ, Gravenstein JS. Computer-assisted capnogram analysis. J Clin Monit 1987;3:194-200.
3. 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.
4. Pascucci RC, Schena JA, Thompson JE. Comparison of a sidestream and mainstream capnometers in infants. Crit Care Med 1989;17:560-2
5. Schena J, Thompson J, Crone RK. Mechanical influences on the capnogram. Crit Care Med 1984;12:672-4.
6. Adams AP. Capnography and pulse oximetery. In: Atkins RS, Adams AP (Eds.). Recent Advances in Anaesthesia and Analgesia. London: Churchill Livingston, 1989;155-75.
7. Bhavani-Shankar K, Moseley H, Kumar AY, Delph Y. Anaesthesia and capnometry. (Review article). Can J Anaesth 1992;39:617-32.
8. Kalenda Z. Mastering Infrared Capnography. The Netherlands: Kerckebosch-Zeist, 1989
