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Bhavani Shankar Kodali MD

Capnogram recorded during general anesthesia for cesarean section

Capno Clips

 Bhavani Shankar Kodali MD



 Capnogram recorded during general anesthesia for cesarean section.

The slope of the phase III is increased. This is a normal physiological variation. Airway obstruction can result in an increase in the phase III as well. Depending on the severity of airway obstruction, phase II can also be prolonged.

Occasionally, a phase IV can also occur in capnograms recorded during anesthesia in pregnant subjects.



Bhavani-Shankar et al. Canadian Journal of Anaesthesia 1992;39:617-32.

Shankar KB et al. Arterial to end-tidal carbon dioxide difference during cesarean section anaesthesia. Anaesthesia 1986;41:698-702.

Shankar KB et al. Arterial to end-tidal carbon dioxide difference during  anaesthesia for tubal ligations. Anaesthesia 1987;42:482-6

Ripple effect

Capno Clips

Bhavani Shankar Kodali MD


This capnogram was recorded during low frequency controlled ventilation. Cardiogenic oscillations shown during the expiratory plateau and the descending limb waveform occurring as a result of movement of gases in the airway due to cardiac pulsations.

Biphasic carbon dioxide waveform in severe kyphoscoliosis

Biphasic carbon dioxide waveform in severe kyphoscoliosis



Carbon dioxide waveform recorded in a patient with severe kypho-scoliosis. The CO2 waveform has two humps. Kyphoscoliosis resulted in a compression of the right lung. The compressed right lung had a relatively high airway resistance, was poorly ventilated, and was relatively hypercapnic, whereas the left lung had a relatively low airway resistance, was hyperventilated, and was relatively hypocapnic. Under these circumstances, relatively hypocapnic gas from well ventilated, low airway resistance lung reached the CO2 analyzer first causing first distinct low peak, and relatively hypercapnic gas from poorly ventilated, high airway resistance lung reached the CO2 analyzer last causing second distinct high peak.

Reference :

Nichols K, Benumof, JL. Biphasic carbon dioxide excretion from a patient with severe kyphoscoliosis. Anesthesiology 1989;71:986-7 (with permission).






Signature capnogram


Capno Clips

 Bhavani Shankar Kodali MD


Signature capnogram

Capnogram recorded during the use of Bain anesthetic system / Mapelson D. The base line is elevated from zero. During inspiration, there a small rebreathing wave due to inhalation of carbon dioxide. The extent of CO2 rebreathing depends FGF, tidal volume, and respiratory frequency. Red indicates inspiration.

A similar capnogram has been reported during closed circuit anesthesia and IPPV where soda lime was totally exhausted as explained below. 

The only difference observed between the two capnograms is that the signature wave during inspiration in the case of exhausted CO2 absorbent is closer to the expiratory waveform than that during bain circuit (see below).


Bhavani-Shankar K et al. Canadian Journal of Anaesthesia 1992;39:617-32.

Adams AP. Capnography and pulse oximetry. In:Atkins RS, Adams AP (Eds). Recent Advances in Anaesthesia and Analgesia. London:Chruchill Livingstone, 1989:155-75.







        The case report on "Failure To Detect CO2-absorbent Exaustion:  Seeing and Believing" by Pond et al is an interesting reading.1  However, the interpretation of the abnormal capnogram as obtained by the authors (figure above) warrants further analysis.

First of all, the differential diagnosis of the abnormal capnogram could be a curare cleft capnogram (if the second peak occurred during expiration), or a rebreathing capnogram (if the second peak occurred during inspiration).2  Understandably, the authors were not certain if the second peak was a part of expiration or inspiration because the capnographs do not have a device yet for marking inspiration and expiration on the time capnogram, thereby delaying the diagnosis of the problem.3,4

Secondly, the mechanism underlying the causation of the abnormal capnogram needs further elucidation. If it was simple dilution of expired gas by the fresh gas, then it should have resulted in a capnogram similar to the computer generated capnogram (fig.3) with a uniform rise in the horizontal baseline.  However, the capnogram obtained by the authors resembles very much  a 'signature capnogram,'  which is classically obtained during the use of rebreathing circuits such as Bain anesthetic system or Mapelson D circuit.2 In the absence of CO2 absorption, the closed circuit functions as a rebreathing circuit. The only difference between the two circuits, under the circumstances described, is that the fresh gas flow is added to the circuit at the patient end in the Bain or Mepelson D system, whereas it is at the machine end in the circle system. Therefore, before the next inspiration, the inspiratory limb of the closed system consists of predominantly CO2 rich gases at the patient end, and predominantly fresh gases (gases accumulated  during the expiratory pause resulting in a further decrease of  the CO2 concentration) towards the machine end of the inspiratory limb.  During inspiration (shown in     ), the relative differences in the CO2 concentration in the inspired limb results in an inspiratory peak (which is less than the expiratory peak), followed by an inspiratory dip in the CO2 concentration, thereby producing the characteristic shape of the capnogram (fig 1).

Lastly, a faulty expiratory valve has been stated as one of the differential diagnosis of the abnormal capnogram. But a sharp decline in the CO2 concentration at the end of the expiratory plateau (the angle between the plateau and the inspiratory downstroke, also known as beta angle, of nearly 90 degrees) rules out this possibility.3,4,5 The beta angle is more obtuse in the capnograms obtained during valve dysfunction. Moreover, the expiratory plateau is usually prolonged in these circumstances to include a part of inspiration as well. 3,4
(Animated version of the capnogram produced with permission from authors reference 1)


1.   Pond D, Jaffe RA, Brock-Utne JG. Failure to detect CO2-absorbent exhaustion: Seeing and Believing. Anesthesiology 2000;92:1196-8.

2.   Bhavani-Shankar K, Moseley H, Kumar AY, Delph Y.  Capnometery and Anaesthesia: Review article.   Can J Anaesth 1992;39:6:617-32.

3.    Yasodananda Kumar A, 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.    Bhavani-Shankar K, Kumar AY, Moseley HSL, Ahyee-Hallsworth R.  Terminology and the current limitations of time capnography: A brief review. J Clin Monit 1995;11:175-82.

5.    Pyles ST, Berman LS, Modell JH. Expiratory valve dysfunction in a semiclosed circle anesthesia circuit - verification by analysis of carbon-dioxide waveform.  Anesth Analg 1984;63:536-7.


Endobronchial intubation

Endobronchial intubation

Right mainstem intubation

Endotracheal tube pulled back into the trachea




A biphasic carbon dioxide elimination waveform recorded in a patient with no known lung disease who was found to have a right main-stem bronchial intubation. 

This capnogram probably occurred as the tip of the endotracheal tube changed moved in out of right main bronchus during respiratory cycle. This resulted in partial obstruction to gases from left lung thereby prolonging  expiratory time from left lung. The initial peak is due to the carbon dioxide  from well ventilated right lung. The second peak is most likely due to prolonged expiratory time of poorly ventilated left lung.


Gilbert D, Benumof JL. Biphasic carbon dioxide elimination waveform with right mainstem bronchial intubation.  Anesth Analg 1989;69:829-32 (with permission).