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 (V_d,an) and alveolar tidal volume (V_A) in ventilated neonates with respiratory distress. Objective: The aim of this study was to determine the differences in V_d,an and V_A in ventilated infants between the early and recovery phases of respiratory distress using volumetric ­capnography (V_cap) 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 (V_T), and performed V_cap based on waveforms of ventilator graphics and capnograms. V_d,an and V_Awere 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 V_d,an (mean difference in V_d,an/kg = 0.57 mL/kg; 95% confidence interval [CI], 0.38–0.77; mean difference in V_d,an/V_T = 0.10; 95% CI, 0.07–0.14) and V_A (mean difference in V_A/kg = –0.60 mL/kg; 95% CI, –0.94 to –0.27; mean difference in V_A/V_T = –0.12; 95% CI, –0.15 to –0.09), despite no difference in V_T. Conclusions: We evaluated changes in V_d,an and V_A during mechanical ventilation using V_cap based on waveforms. The increase in V_d,an and decrease in V_A suggested dilation of the airways and collapse of the alveoli in ventilated infants with low lung compliance.