ObjectivesEnd tidal carbon dioxide (ETCO2) monitoring can facilitate identification of successful intubation. The aims of this study were to determine the time to detect ETCO2following intubation during resuscitation of infants born prematurely and whether it differed according to maturity at birth or the Apgar scores (as a measure of the infant’s condition after birth).DesignAnalysis of recordings of respiratory function monitoring.SettingTwo tertiary perinatal centres.PatientsSixty-four infants, with median gestational age of 27 (range 23–34)weeks.InterventionsRespiratory function monitoring during resuscitation in the delivery suite.Main outcome measuresThe time following intubation for ETCO2levels to be initially detected and to reach 4 mm Hg and 15 mm Hg.ResultsThe median time for initial detection of ETCO2following intubation was 3.7 (range 0–44) s, which was significantly shorter than the median time for ETCO2to reach 4 mm Hg (5.3 (range 0–727) s) and to reach 15 mm Hg (8.1 (range 0–827) s) (both P<0.001). There were significant correlations between the time for ETCO2to reach 4 mm Hg (r=−0.44, P>0.001) and 15 mm Hg (r=−0.48, P<0.001) and gestational age but not with the Apgar scores.ConclusionsThe time for ETCO2to be detected following intubation in the delivery suite is variable emphasising the importance of using clinical indicators to assess correct endotracheal tube position in addition to ETCO2monitoring. Capnography is likely to detect ETCO2faster than colorimetric devices.