Reduction in minute alveolar ventilation causes hypercapnia in ventilated neonates with respiratory distress

Abstract

Hypercapnia occurs in ventilated infants even if tidal volume (V T) and minute ventilation (V E) are maintained. 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. We investigated the relationship between dead space and partial pressure of carbon dioxide (PaCO 2) and assessed V A. Intubated infants (n = 33; mean birth weight, 2257 ± 641 g; mean gestational age, 35.0 ± 3.3 weeks) were enrolled. We performed volumetric capnography (V cap), and calculated V d,phys and V A when arterial blood sampling was necessary. 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). Normocapnia (82 measurements; 35 mmHg ≤ PaCO 2 < 45 mmHg) and hypercapnia groups (57 measurements; 45 mmHg ≤ PaCO 2) were classified. 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. 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. Conclusion: Reduction of V A in well-ventilated neonates induces hypercapnia, caused by an increase in V d,phys .

Physiological dead space and alveolar ventilation in ventilated infants

“…10 A previous study has shown that a reduction in alveolar ventilation resulted in hypercapnia in ventilated infants with respiratory distress syndrome (RDS). 11 The aim of this study was to determine if the physiological dead space in prematurely born infants with RDS or evolving/established bronchopulmonary dysplasia (BPD) was greater than in term controls with no respiratory disease. We further aimed to determine whether the size of the dead space influenced the alveolar ventilation in mechanically ventilated infants.…”

Large difference between Enghoff and Bohr dead space in ventilated infants with hypoxemic respiratory failure

“…We had previously reported the use of volumetric capnography based on ventilator graphics and capnograms in ventilated neonates in NICUs by using a commonly used lightweight mainstream capnometer. 8,9 We hypothesized that ventilated infants with hypoxemic respiratory failure (HRF) show a large difference between V d, Enghoff and V d, Bohr . Thus, the objective of this study was to measure both V d, Enghoff and V d, Bohr, and to detect low V/Q mismatch and right-to-left shunting in intubated neonates by using volumetric capnography based on ventilator graphics and capnograms.…”