Mainstream monitoring is an ideal choice for intubated patients. It provides a non-diverting, crisp, accurate CO2 waveform with no time delay, and does not require use of a scavenger system to collect anesthesia gases. Because patient secretions or high humidity do not contaminate the sensor, it is a preferred choice for these patient conditions or environments. Mainstream EtCO2 sensor uses a common extension server, providing clinical versatility to use with the same monitor. No calibration is required. The sensors remain stable over time with continual and automatic validated calibration information.