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1. CAPNOGRAPHY
Capnography is an effective method to diagnose early respiratory
depression and airway disorders, especially during anaesthesia, leading
to a reduction in serious complications . Capnography provided more
safety in monitoring patients during anaesthesia.
The term capnography refers to the noninvasive measurement of the
partial pressure of carbon dioxide (CO2) in exhaled breath expressed as
the CO2 concentration over time.
 Normal range for capnography?
between 35-45 mm Hg
What are the different types of capnography?
There are two types of capnography,
1)mainstream
2)sidestream.
Mainstream capnography is characterized as invasive and non-diverting,
meaning that the measurement of the ETCO2 is done at the airway, or the
sample site, thus providing a real-time measurement of the carbon dioxide
pressure.
Sidestream, on the other hand, is non-invasive and diverting. This means
that the gas sample is transported from the sample site through a plastic
tube and analyzed in a sample cell. This results in a couple seconds delay of
the analysis and a possible distortion of the analysis, which can be
consequential in an emergency situation.
However, the non-invasive nature of sidestream capnography means that it
can be easily used on non-intubated patients, unlike mainstream
capnography, which can be difficult to adapt to non-intubated patients. In

2. addition, mainstream capnography can be prone to technological
difficulties and fragility, which is less of an issue with sidestream
capnography.
Mechanism
 The essential mechanism of capnography is basic. It is grounded on the
property that carbon dioxide (CO2) absorbs infrared radiation. When the
patient exhales, a beam of infrared light is passed over the gas sample
on a sensor. The presence or lack of CO2, is inversely indicated by the
amount of light that passes through the sensor. High CO2 levels are
indicated by low infrared, and low CO2 levels result in high amounts of
light.
 What is measured by the capnograph is known as the End Tidal CO2
(ETCO2) or the amount of (or partial pressure of) the carbon dioxide
released at the end of expiration, an essential component of measuring
cardiac output.
A normal capnography waveform looks like *image*. The length of the
wave represents the time, while the height of the wave represents the
amount of CO2 in the exhaled breath. Thus faster breathing is
represented by a relatively short duration of the waveform, whereas
slower breathing is shown with longer waveforms. On the other axis, the
taller the waveform, the more ETCO2 is in the breath. Inspiration,
therefore, is shown on the waveform by a drop of the CO2 levels to zero.
NORMAL CAPNOGRAM
4 phases
 Phase I (inspiratory baseline) reflects inspired gas, which is normally devoid of carbon dioxide.
 Phase II (expiratory upstroke) is the transition between VDana, which does not participate in gas
exchange, and alveolar gas from the respiratory bronchioles and alveoli.

3.  Phase III is the alveolar plateau. Traditionally, PCO2 of the last alveolar gas sampled at the
airway opening is called the PETCO2.
 Phase 0 is the inspiratory downstroke, the beginning of the next inspiration