Ventilated Infants Have Increased Dead Space and Lower Alveolar Tidal Volumes during the Early versus Recovery Phase of Respiratory Distress.

Background: Few studies have reported the measurement of anatomical dead space (Vd,an) and alveolar tidal volume (VA) in ventilated neonates with respiratory distress.

Objective: The aim of this study was to determine the differences in Vd,an and VA in ventilated infants between the early and recovery phases of respiratory distress using volumetric -capnography (Vcap) based on ventilator graphics and capnograms.

Methods: This study enrolled twenty-five ventilated infants (mean birth weight, 2,220 ± 635 g; mean gestational age, 34.7 ± 3.3 weeks). We adjusted respiratory settings to maintain appropriate oxygenation and tidal volume (VT), and performed Vcap based on waveforms of ventilator graphics and capnograms. Vd,an and VAwere measured in infants with respiratory disorders, immediately after intubation (early phase) and subsequently when they were clinically stable (recovery phase).

Results: The early phase, with lower dynamic lung compliance, required a higher level of ventilator support, not positive end-expiratory pressure, than the recovery phase. There were significant differences between the early and recovery phases for Vd,an (mean difference in Vd,an/kg = 0.57 mL/kg; 95% confidence interval [CI], 0.38-0.77; mean difference in Vd,an/VT = 0.10; 95% CI, 0.07-0.14) and VA (mean difference in VA/kg = -0.60 mL/kg; 95% CI, -0.94 to -0.27; mean difference in VA/VT = -0.12; 95% CI, -0.15 to -0.09), despite no difference in VT.

Conclusions: We evaluated changes in Vd,an and VA during mechanical ventilation using Vcap based on waveforms. The increase in Vd,an and decrease in VA suggested dilation of the airways and collapse of the alveoli in ventilated infants with low lung compliance.