However, even when V T or V E are maintained, hypercapnia can occur. Tighter control of PaCO 2 may be achieved in mechanically ventilated infants by setting appropriate minute ventilation ( V E), defined by tidal volume ( V T) and the respiratory rate (RR). Both hypercapnia and hypocapnia can contribute to brain damage in immature infants. The hypercapnia group had lower V A (123 (IQR, 87–166) ml/kg/min) than the normocapnia group (151 (IQR, 115–180) ml/kg/min), with no difference in V E.Ĭonclusion: Reduction of V A in well-ventilated neonates induces hypercapnia, caused by an increase in V d,phys.Īn optimal arterial carbon dioxide concentration, measured by the partial pressure of carbon dioxide (PaCO 2), is critical during mechanical ventilation. The hypercapnia group had higher V d,phys (median 0.57 (IQR, 0.44–0.67)) than the normocapnia group (median V d,phys/ V T = 0.46 (IQR, 0.37–0.58)], with no difference in V T. Normocapnia (82 measurements 35 mmHg ≤ PaCO 2 < 45 mmHg) and hypercapnia groups (57 measurements 45 mmHg ≤ PaCO 2) were classified. PaCO 2 was positively correlated with alveolar dead space ( V d,alv) ( r = 0.54, p < 0.001) and V d,phys ( r = 0.48, p < 0.001), but not Fowler dead space ( r = 0.14, p = 0.12). We performed volumetric capnography ( V cap), and calculated V d,phys and V A when arterial blood sampling was necessary. Intubated infants ( n = 33 mean birth weight, 2257 ± 641 g mean gestational age, 35.0 ± 3.3 weeks) were enrolled. We investigated the relationship between dead space and partial pressure of carbon dioxide (PaCO 2) and assessed V A. We hypothesised that increased physiological dead space ( V d,phys) caused decreased minute alveolar ventilation ( V A alveolar ventilation ( V A) × respiratory rate) in well-ventilated infants with hypercapnia. Hypercapnia occurs in ventilated infants even if tidal volume ( V T) and minute ventilation ( V E) are maintained.
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