Both mainstream and sidestream modules use infrared absorption to detect the number of CO2 molecules in exhaled gas. Specifically, a beam of infrared light with a specific wavelength is shone from one side of the gas chamber, passing through the gas chamber and radiating onto the infrared detector on the other side of the gas chamber. (The mainstream gas chamber is the adapter, the sidestream gas chamber is built-in, and the gas flowing in the gas chamber is the patient’s exhaled gas).
The CO2 in the flowing gas in the gas chamber will absorb energy at this specific wavelength, so the energy signal detected by the infrared detector on the other side of the gas chamber will change with the change in CO2 concentration. The software calculates the number of CO2 molecules in the gas chamber by the change in absorbed energy, and then calculates the CO2 concentration in the exhaled gas.
Both mainstream and sidestream are used to detect EtCO2 and respiratory rate. Generally speaking, sidestream monitoring is suitable for emergency and post-anesthesia recovery situations. For intubated patients, mainstream monitoring is preferred.
When the mainstream module is connected to the monitor for the first time, zeroing must be performed. When changing the type of adapter for the mainstream module, such as from disposable to reusable, zeroing must be performed. When changing a disposable adapter, it is recommended to perform zeroing, but it is not mandatory. Zeroing is not allowed when the mainstream module has no adapter or the sidestream module has no gas connection system. During the zeroing process, it must be ensured that no CO2 enters the zeroing gas path, including the CO2 in the patient’s exhalation and inhalation. Each zeroing operation takes about 15-20 seconds.
Zeroing is not calibration. For the mainstream module, zeroing is to eliminate the impact of changing adapters on the measurement results, because the window material of the disposable adapter and the reusable adapter is different. For the sidestream module, the zeroing operation is to eliminate the possible impact of the difference in the dehydration column and the sampling gas path on the measurement results.
Sidestream CO2 modules and mainstream modules do not need any form of calibration during daily use, because we have done range calibration at the factory, and our design can ensure that the measurement accuracy meets the requirements within the life cycle. The continuous use life of the air pump of the sidestream CO2 module has two configurations of 500 hours and 20000 hours, which can be replaced according to the needs of users. If the user’s continuous use time is particularly long when purchasing our sidestream module, it is recommended to configure a 20000-hour life air pump at the factory.
The normal range of EtCO2 is between 32-45mmHg, about 5%. Both mainstream and sidestream modules can measure up to 150mmHg (about 20%), and the respiratory rate can measure up to 150 times/minute. The measurement accuracy calculated in brief is as follows: • 0 – 40mmHg ±2mmHg • 41 – 60mmHg ±5% of the reading • 71 – 100mmHg ±8% of the reading • 101 – 150mmHg ±10% of the reading.