Capnography is a technique that is used to detect the carbon dioxide concentration in exhalation gases. Capnometer uses infrared light in sensors in order to detect the CO2. Capnography is an important parameter in current day patient monitoring.

1. CAPNOGRAPHY
BASICS OF
Dr. GT Wijesinghe. MBBS

2. WHAT IS CAPNOGRAPHY
• Capnography is a technique that is used to measure the exhaled
concentration of carbon dioxide
• The concentration of exhaled CO2 correlates to the arterial concentration of
CO2
• ETCO2 represents partial pressure of CO2 in air at the end of tidal expiration
(see next slide)

4. ETCO2
• Normal range 35-45 mmHg
• Approximately equivalent to arterial Pco2
• Real time values are given by mainstream capno-detectors
• Important parameter in patient monitoring

5. HOW CO2 LEVELS IN TUBES ENDED UP IN
DISPLAY?
• measured through the use of infrared light absorption by CO2
1. A beam of infrared light is passed through the gas sample
2. The presence of CO2 causes less light to fall on the sensor;
CO2 absorbs infrared light
3. The sensor rapidly detect and measure the infrared light falls
on it
4. The sensor output is processed and calibrated according to
the CO2 level

6. CAPNOGRAPHY VS CAPNOMETRY
• Capnography provides a waveform in a graphic format
• Capnometry provides numeric values of CO2 level

7. MAINSTREAM AND SIDE STREAM
DETECTORS
Mainstream :
• Mainstream detector is located in the pathway of airway circuit
• May increase the volume of undesirable dead space
• Produce real time values or graphs
Side stream :
• Side stream detector is located away from the tubal system and
connected by a small diameter tubing with the airway circuit
that allows gas sampling

8. MAINSTREAM SIDE STREAM

9. • End tidal expiration
• No further gas exchange
• Available gases rich in CO2
• ETCO2 : Numeric value shown in
display
• Tidal inspiration
• Gases flow in (no CO2)
• Alveolar plateau
• Alveolar gases comes out
• Slow, further rise in PCO2
• Expiratory phase
• Dead space gases comes out
• Rapid rise in PCO2
• Fresh gas inspiration
• Air is filled with ventilator gases
• No CO2
CO2 detector
A
B
C
E
D

11. Rapid upstroke : expiration of dead space gases
Plateau : expiration of alveolar gases

12. NOTE
• Expiration time is greater than inspiration time
• Height of graph is proportional to the tidal volume
• Height of graph is indirectly represent the cardiac output (CO)*
1. Adequate cardiac output is required to
bring the CO2 from tissues to the lung
2. Adequate ventilation is required to
deliver that CO2 to external atmosphere
* MH Weli et al, showed a high correlation between ETCO2 and cardiac output during CPR

13. CLINICAL APPLICATION
• To diagnose hypoventilation during procedures under sedation
• Endotracheal tube confirmation and monitoring
• Measure arterial PCO2 levels during mechanical ventilation
• To diagnose ventilation problems instantly; ETCO2 is superior
to SPO2 in this case.
• Assist in cardio-pulmonary resuscitation

14. CAPNOGRAPHY IN NORMAL VS BRONCHOSPASM

15. EXAMPLES FOR DIFFERENT CONDITIONS
Hypoventilation
Hyperventilation

16. Difficult expiration in asthma
Shock with reducing cardiac
output

17. • THANK YOU