Volumetric capnography slopes in ventilated term and preterm infants

Abstract

Abstract Objective: To assess whether the slopes of volumetric capnography differ in preterm compared to term-born ventilated newborn infants and whether they are related to gestational age and the duration of ventilation. Approach: The slopes of phase II (SII) and III (SIII) of volumetric capnographs were measured in ventilated term and preterm infants at King’s College Hospital NHS Foundation Trust. The correlations of the slopes with gestational age (GA), duration of invasive ventilation and fraction of inspired oxygen (FIO2) were assessed. The slopes were normalised by multiplying the results with the expiratory tidal volume (VT) measurement. Main results: Fifty-six infants (44 preterm) were assessed. The preterm infants had a median (IQR) gestational age of 26 (25–29) weeks and were ventilated for 8 (3–32) days with a VT of 5.4 (4.1–6.8) ml kg−1. The term infants had a gestational age of 39 (37–40) weeks and were ventilated for 1 (1–6) day with a VT of 4.0 (3.6–5.3) ml kg−1. The SII (85.9 (76.2–98.4) mmHg) and SIII (16.5(10.0–21.9) mmHg) of the preterm infants were not significantly different compared to the SII (88.0 (74.6–110.0) mmHg) and SIII (13.5 (9.2–15.9) mmHg) of term infants (p = 0.625 and p = 0.144 respectively). SII was not significantly related to GA, duration of ventilation or FIO2. SIII was positively related to the duration of ventilation (r = 0.729, p < 0.001) and FIO2 (r = 0.704, p < 0.001). Significance: The volumetric capnography phase III slope was steeper in infants with higher ventilatory requirements, hence could potentially be used as an index of disease severity in ventilated newborns.