Title: Basic Patient Monitoring For Anesthesia End tidal CO2
1Basic Patient Monitoring For AnesthesiaEnd tidal
CO2
- Dr. Jeffrey Elliot Field
- HBSc, D.D.S. , Diplomat of the National dental
Board of Anesthesia, - Fellow of The American Dental Society of
Anesthesia
2HOW DOES IT WORK?/PHYSIOLOGY
- Carbon dioxide absorbs infrared light with a
wavelength of 4.3m m. - Light at this wavelength is shone through a gas
sample and the absorption is proportional to the
carbon dioxide concentration. - A sample of expired gas is withdrawn from the
anaesthetic circuit by a pump and analyzed inside
the machine.
3WHAT DOES IT TELL US?
- Valuable information can be obtained from the
continuous measurement of carbon dioxide. - At the most basic level the regular rise in
carbon dioxide at the end of respiration can be
used to determine respiratory rate, and
regularity of respiration.
4WHAT DOES IT TELL US?/ CONTINUED.
- 2)The shape of the capnograph (the plot of carbon
dioxide against time) is used to assess pulmonary
function. - The carbon dioxide level should rise rapidly
during the first part of exhalation and then
flatten off - the "alveolar plateau". If there is
pulmonary disease or poor lung perfusion
(secondary to poor cardiac output) the alveolar
plateau disappears. - The level of carbon dioxide at the end of
expiration (end tidal carbon dioxide, etCO2) is
normally within a few mmHg of the arterial carbon
dioxide level and therefore a predictable measure
of arterial CO2. - EtCO2 is very useful for assessing adequacy of
ventilation both during spontaneous respiration
and when using a ventilator.
5ETCO2 continued
- EtCO2 is very useful for assessing adequacy of
ventilation both during spontaneous respiration
and when using a ventilator. - But the most important thing ETCO2 tells us in a
sedated patient is - ARE THEY BREATHING
- In an intubated patient ETCO2 will initially
confirm proper placement of the endotracheal
tube. - As the case progresses ETCO2 will continue to
confirm that the tube is placed properly and has
not moved. - Finally the adequacy of ventilation can be
continuously assessed.
6Normal Values
- In a sedated patient it is not so much a normal
value but a baseline value for that particular
patient that we look at. Changes in this
baseline value will let us know whether our
patient is breathing normally, hyperventilating
or hypoventilation. - In an intubated patient a normal end tidalCO2
value is 40 mm of mercury. - ETCO2 Less Than 35 mmHg "Hyperventilation"
ETC02 Greater Than 45 mmHg "Hypoventilation"
7CO2 continued.
- There are two main graphs that we look at which
are a function of the sweep speed. - At high sweep speed we get a wave form of the CO2
from each breath which is known as the capnogram.
There is only one normal shape for a capnogram - At first there is a rapid rise as the dead space
gas comes out of the major airways. - Then there is a plateau which has a slow rise.
- Finally there is a rapid decline as the next
breath enters the patient.
8Normal Capnogram
9Explanation of the normal capnpgram
A to B is post inspiration/dead space exhalation,
B is the start of alveolar exhalation, B-C is the
exhalation upstroke where dead space gas mixes
with lung gas, C-D is the continuation of
exhalation, or the plateau(all the gas is
alveolar now, rich in C02). D is the end-tidal
value the peak concentration, D-E is the
inspiration washout.
10Causes Of A Poor Plateau
- Kinked tube (intubated patients only)
- Herniated cuff (intubated patients only)
- Bronchospasm (intubated and non-intubated
patients) - Any obstruction that limits expiration( eg
mucous on the tube, COPD, asthma, foreign body
obstruction.
11Neromuscular Blocker Wearing Off and patient
initiating breathing against the ventilator(
intubated patients only)
12Camel Wave
Causes- 1)Unequal emptying of lungs(
pnemothorax). Seen in intubated and non-intubated
patients 2)Lateral position 3)Tube touching
carina
13Why capnography is better than pulse oximetry
symmetry in assessing a cessation in breathing.
Note what happens when the patient stops
breathing.
The pulse oximeter lags way behind the
capnograh in picking up a cessation in breathing.