Capnography

Capnography is commonly known as medical respiratory surveillance. It is used to monitor the CO2 concentration of human respiratory gases to detect any lung malfunction during medical treatments such as:
  • Mechanical Ventilation and Intubation
  • Pediatric sedation
  • Postoperative wake-up
  • Emergency transport
As capnography can give an early warning of hypoxia (low oxygen levels), which can lead to serious brain damage, it is a widely accepted method to ensure the health and safety of patients during many medical treatments. Medical associations like the American Society of Anesthesiologists (ASA) and Association of Anaesthetists of Great Britain and Ireland (AAGBI) made capnography mandatory to monitor ventilation e.g. during moderate to heavy sedation.
Besides the use of capnography for intensive care, it can also be used for bodyplethysmography to detect any kind of lung dysfunction like asthma, poor lung compliance or chest breathing. Ever smaller devices make capnography now suitable for home medical usage, e.g. to detect hyperventilation.

Basic Principle of Capnography

For capnography the CO2 concentration of inhaled air and exhaled air is continuously monitored and the waveform and relevant parameters will be displayed. The basic waveform of a capnogram is shown in the picture below. From the inhalation baseline (ambient CO2 concentration) the CO2 level rises while exhalation and forms a plateau. Immediately before inhalation the CO2 level will show its highest level, the so called end-tidal CO2 concentration, or Et-CO2.
Example for Capnograph
The Et-CO2 concentration is taken as a measure for the ability to carry away CO2 from the lungs.
doctor and patient with ventilation system

While the inhalation baseline contains about 400 ppm CO2, the typical Et-CO2 value is in the range of 40.000 and 50.000 ppm.


Besides the current Et-CO2 value, continuous monitoring allows to see rising and falling trends in the Et-CO2 and the waveform itself will tell if the lung functions correctly. While the above picture shows the waveform of a healthy person, there are several variations,
that can indicate lung dysfunctions like asthma, hypoxia or hyperventilation.


As the CO2 capnography levels react in real time to any change of a patient's condition, it saves precious time in taking counter measures and prevents patients from severe damage.


Recommended Sensors for CO2 concentration measurements: