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Interpret your capnogram

Bhavani Shankar Kodali MD
Compiled: by Ahalya Kodali
 

This section provides a variety of capnograms put together in one group. Several E-mails have prompted us to compile this section. If you happen to see a capnogram and you wanted to know what the underlying cause is, this section should provide an answer. Match your capnogram against the following; the explanation is either self explanatory or' click' on the 'detail' to open a new window. Close the window to return to this page. Majority of these capnograms have bee discussed elsewhere in the website. If you do not see a matching capnogram, please E-mail us (capnoman@gmail.com) with your explanation or explanation referenced elsewhere for inclusion.

 

 

Air-leak - Loose connection between sampling tube
and capnograph / broken connection or filter.

Details
Following one lung transplantation.
If the tip of the endotracheal tube is too close to the carina thereby resulting in differential lung ventilation due to partial obstruction. (see 15 and 23)

 

Rebreathing capnogram of Mapleson D circuit.
Bain circuit.

Details
Exhausted CO2 absorber. See below ()

 

 

Cardiogenic oscillations - Ripple effect - Seen during low frequency ventilation.

Details

 

 

Bronchospasm / COPD / Emphysema/ obstructed endotracheal tube -Slanting and prolonged phase 2 and increased slope of phase 3 (see 14)

 

 

Contamination of capnograph
Trend showing abrupt elevation of baseline and capnogram. See 43

 

 

Trend capnogram during cardiac arrest / resuscitation.

 

 

Upward slanting of phase 4. A normal variant in pregnant women during anesthesia.

Details

 

 

Trend showing gradual elevation of baseline.
Rebreathing

 

 

Curare cleft (see 10)

 

 

Resembling curare cleft due to an artifact created by surgeon leaning on the chest, or pushing against the diaphragm during expiration.
Partial disconnect of main stream capnometer

Details

 

 

Dilution of expiratory gases by the forward flow of fresh gases during the later part of expiration when expiratory flow rate decreases below the forward gas flow rate.

 

 

Elevation of base line- A classic representation of rebreathing.

Exhausted CO2 absorber

 

 

A gradual decrease in end tidal carbon dioxide can occur during reduced metabolism, hypothermia, hyperventilation, small tidal volume ventilation due to inadequate alveolar sampling, and leaks in the sampling system,decrease in cardiac output see 13

 

 

Occasionally, there can be a reverse phase 3 slope seen in patients with emphysema. Most like this may be due to destruction of alveolar capillary system in emphysematous lungs resulting in the delivery of carbon dioxide to expired gases.

 

 

Endobronchial intubation may not result in a characteristic waveform. However, occasionally, it may be like the one seen in COPD or the above. Read the 3 sections.

Details Details Details Details see (15)

 

 

The CO2 waveform has two humps. Kyphoscoliosis resulted in a compression of the right lung. Differential lung emptying. Details

 

 

Esophageal intubation.

 

 

Esophageal intubation: Small CO2 spikes. Esophageal or gastric CO2 due to mask ventilation

 

 

Warming up CO2 analyzer is necessary before it begins recording CO2 wave forms.

 

 

The monitor will zero periodically. Will show CO2 numerical value with no waveform.

 

 

Ventilator IMV breath during spontaneous ventilation.

 

 

Sticking inspiratory valve - Inspiratory flip - Red indicates possible rebreathing

 

 

Air leak due to a broken connection between sampling tube and capnograph Details see (1)

Lung transplant - Dual capnogram Details see 1, 15 and 23

 

 

Increased CO2 due to hypoventilation, hypermetabolic states and rebreathing. See 8, 39

 

 

Capnogram during spontaneous ventilation in adults (see 27)

 

 

These capnograms can occur in children and neonates. Variations are normal and due to faster respiratory rates, smaller tidal volumes, relatively longer response time of the capnographs. Recent technological advances such as micro-stream analyzers are reducing the artifacts due to faster response time and thereby producing normal looking capnograms even in children and neonates.

 

 

Sampling problems such air or oxygen dilution during nasal or mask sampling of carbon dioxide in spontaneously breathing patients.

 

 

Slit sampling tube can result in a pig tail capnogram. A variation of 23 Details

 

 

A terminal upswing at the end of phase 3, known as phase 4, can occur in pregnant subjects, obese subjects and low compliance states. Details see also physiology section-phase 4.

Expiratory valve malfunction can result in prolonged abnormal phase 2 and phase 0.Details

Inspiratory valve malfunction predominantly results in abnormal phase 0. Details

Esophageal intubation resulting few abnormal capnograms with relatively normal initial CO2 numerical values. Details

Hyperventilation gradually results in lowering of ETCO2 values. see 13

Hypoventilation gradually increases CO2 values with normal base line. see 8 and 25

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Rebreathing producing gradual elevation of base line and ETCO2 values. See 8

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Carbonated beverages in the stomach can result in abnormal capnograms with progressively decreasing CO2 values following esophageal intubation. See other variations 17, 18, 37

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Unrecognized exhaustion of CO2 absorber resulted in substantial rebreathing and rising ETCO2 values. The closed circuit without functioning absorber mimicked Mapleson D circuit.   Details

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Contamination of capnometer results in the sudden elevation of base line as well as ETCO2 values. See 5