Background Positive pressure ventilation (PPV) remains the cornerstone of respiratory support after birth. Although, gas going in and out of the lung can be measured with a respiratory function monitor, gas exchange (or effective ventilation) may only be determined by presence of exhaled CO₂.

Aim To identify non-invasive clinical tools to assess lung aeration in infants receiving PPV after birth.

Methods Deliveries of preterm infants < 32 weeks gestation were attended. During PPV we measured airway pressures, gas flow and tidal volume (V_T), exhaled CO₂, heart rate and oxygen saturation. We compared delivered V_T and heart rate before and after exhaled CO₂ was measured.

Results In 10 preterm infants exhaled CO₂ and respiratory functions were recorded; their mean (SD) birth weight and gestational age was 27 (2) weeks and 902 (287) grams, respectively. A median (IQR) of 23 (17–43) inflations was delivered with no exhaled CO₂. The median (IQR) V_T when no CO₂ was measured was 1.9 (1.0–3.8) mL/kg compared to 8.3 (2.1–10.3) mL/kg when exhaled CO₂ was measured (p<0.0025) 1). The mean (SD) heart rate while no CO₂ was exhaled was 61 (6) beats per minute compared to 104 (41) beats per minute 60 seconds after CO₂ was measured.

Conclusion Delivered V_T and heart rate was significantly lower when no CO₂ was exhaled. The presence of exhaled CO₂ was accompanied by increases in HR. Combined V_T measurements, changes in heart rate and detection of exhaled CO₂ may provide information on lung aeration of infants transitioning after birth.