Understanding Anesthesiology - The Global Regional Anesthesia ...

Capnograph
The capnograph is a monitor within the anesthetic machine which measures the quantity of
carbon dioxide in the exhaled breath. It provides an analog waveform along with a numeric
value. Various determinations can be made based on the characteristics of the waveform.
For example, bronchospasm has a characteristic upslanting pattern on the capnograph that
can be recognized by the astute clinician.
It is normal to have a gradient between alveolar and arterial levels of carbon dioxide, a gradient
which is in the range of 4-8 cmH2O. There are conditions, however, where capnography
will significantly underestimate the arterial blood levels of CO2:
1) Conditions where blood flow to the lungs is impeded, therefore carbon-dioxide is not getting
delivered to the lungs. Examples include cardiac arrest and pulmonary embolus.
2) Conditions where a true alveolar gas sample is not being obtained (such that deadspace is
sampled instead). Examples include the use of very small tidal volumes or any condition
causing obstruction to expiration such as acute bronchospasm due to asthma exacerbation
or anaphylactic reaction.
Related Glossary Terms
Anesthetic circuit, CO2 (carbon dioxide) absorber, Esophageal intubation, Intubation
Index
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Chapter 1 - Airway Management
Chapter 2 - Anesthetic Equipment and Monitoring