Respiratory changes in term infants immediately after birth

Introduction: Over 5% of infants worldwide receive breathing support immediately after birth. Our goal was to define references ranges for exhaled carbon dioxide (ECO2), exhaled tidal volume (VTe), and respiratory rate (RR) immediately after birth in spontaneously breathing, healthy infants born at 36 weeks' gestational age or older. Methods: This was a single-centre, observational study at the Royal Women's Hospital in Melbourne, Australia, a busy perinatal referral centre. Immediately after the infant's head was delivered, we used a face mask to measure ECO2, VTe, and RR through the first ten minutes after birth. Respiratory measurements were repeated at one hour. Results: We analysed 14,731 breaths in 101 spontaneously breathing infants, 51 born via planned caesarean section and 50 born vaginally with a median (IQR) gestational age of 39(1/7) weeks (38(3/7) -39(5/7)). It took a median of 7 (4-10) breaths until ECO2 was detected. ECO2 quickly increased to peak value of 48 mmHg (43-53) at 143 s (76-258) after birth, and decreased to post-transitional values, 31 mmHg (28-24), by 7 min. VTe increased after birth, reaching a plateau of 5.3 ml/kg (2.5-8.4) by 130 s for the remainder of the study period. Maximum VTe was 19 ml/kg (16-22) at 257 s (82-360). RR values increased slightly over time, being higher from minute five to ten as compared to the first two minutes after birth. Conclusions: This study provides reference ranges of exhaled carbon dioxide, exhaled tidal volumes, and respiratory rate for the first ten minutes after birth in term infants who transition without resuscitation.