Background End-tidal carbon dioxide (EtCO2) differs from PaCO2 in patients with lung ventilation–perfusion mismatch. There are no data on infants with bronchopulmonary dysplasia (BPD).
Objectives To compare EtCO2 and capnogram of infants with BPD with those of control preterm infants.
Materials and Methods Capnography using a sidestream device (Capnostream-20) was performed (nasal cannula) at 36 weeks of corrected age, in 20 preterm infants (BPD, oxygen dependency 12 cases, absence of respiratory disease eight cases). Respiratory rate, inspiratory time (TI), expiratory time (TE) and duration of the respiratory cycle (TTOT) were measured. EtCO2 values were compared with values simultaneously measured in capillary samples (PcCO2), and the PcCO2–EtCO2 gradient was calculated. Capnograms were analysed and compared.
Results In BPD, compared with control infants: (1) There was a PcCO2–EtCO2 gradient (13 ± 4 vs 0 ± 7 mm Hg, p = 0.001). (2) Respiratory rate was increased (RR 60 ± 16 vs 43 ± 16 bpm, p = 0.009), due to a decrease of both TI and TE. (3) The capnogram showed a greater ascending angle (48 ± 6 vs 42 ± 4 degrees, p = 0.02) at the onset of expiration, a longer initial inspiratory phase, from carbon dioxide plateau to baseline (0.32 ± 0.05 vs 0.24 ± 0.04 s, p = 0.001) and a shorter baseline phase (0.05 ± 0.02 vs 0.08 ± 0.04 s, p = 0.01) (phase durations expressed as ratios over TTOT, in order to standardise for respiratory rate differences).
Conclusion In preterm infants with BPD, inhomogeneous alveolar ventilation–perfusion was suggested and the capnogram showed specific characteristics, which may result from lung abnormalities and require further investigation.