Although there is an opportunity for end-tidal CO₂ (etCO₂) monitoring in nonintubated patients with the developing technology in mainstream and sidestream capnographies, false results can be obtained as a result of obstruction due to water and secretion. Microstream (MST) is a new method developed for CO₂ measurement, based on molecular correlation spectroscopy. In this method, a specific infrared radiation wavelength is used to detect CO₂, which is not affected by the other gases (i.e., O₂, N₂O, He, inhaled anesthetics). In the MST procedure, a low sample flow rate (50 ml/min) is adequate, which makes the procedure useful in different types of patients, such as neonates. MST can be used in intubated and nonintubated patients, and it is widely available for monitoring etCO₂ during NIV [3].