Capnography is used in a wide range of medical applications to obtain critical information about the patient’s health. This can include CO2 excretion, pulmonary perfusion, alveolar ventilation, respiratory patterns, and elimination of CO2 from the anesthesia breathing circuit and ventilator.
How Capnography Works
End-tidal capnography (EtCO2) is the measurement of the concentration of carbon dioxide (CO2) in exhaled breath. The exhaled breath travels through a sample line from the patient to the capnography monitor, also known as capnographs. These monitors usually work on the principle that CO2 absorbs infrared radiation (IR). A beam of infrared light is passed across the gas sample to fall on a sensor. The presence of CO2 in the gas leads to a reduction in the amount of light falling on the sensor, which changes the voltage in a circuit. The analysis is rapid and accurate. Capnographs display a numerical value as well a waveform, which is a graphical depiction of the CO2 concentration in each exhaled breath.
Challenges Associated with Capnography – Water vapor interferes with the proper operation of analytical equipment in a variety of ways:
- Moisture Interference in Infrared Analysis used for CO2 Monitoring & Measurement – Water vapor appears on the scale in the same region as the CO2 peak, making the results difficult to read and introducing inaccuracies based on the operators’ interpretation of the results. Removal of the water, in vapor phase, preserves the CO2 level while eliminating interference.
- Moisture build‐up in Sample Lines – Condensation from the breath gas sample stream can collect in the sample lines, a problem normally found when the fully saturated sample at body temperature is brought into contact with the lines at standard room temperature.
- Moisture Collection in the Sensor Cell – Condensation in the sample will eventually reach the analyzer, and will cause irreparable harm to the sensor and render the equipment unusable. This is a problem commonly found when the fully saturated breath sample (at 37C body temperature) is brought to the analyzer at a colder room temperature.
How Perma Pure dryers using Nafion® membrane tubing technology help:
- Fast response time – instantaneous and continuous moisture transfer
- Fully bio-compatible for surface contact with patient skin
- Removes up to 90% of moisture in breath samples
- Improves accuracy of IR-based EtCO2 measurements by eliminating moisture interference
- Highly selective – removes water vapor while retaining sample analytes
- Prevents condensation to protect medical monitoring equipment
- Reduces dead volume in sample circuit when compared with a water trap.