Determinants of end-tidal carbon dioxide measurement reliability in neonatal ventilation: a bench lung simulation...

End-tidal carbon dioxide (ETCO₂) monitoring is used in the neonatal intensive care unit to estimate arterial carbon dioxide as a measure of ventilation efficacy; however, lung mechanics and circuit-related factors can affect measurement reliability.

Using a bench neonatal lung simulator, we varied lung compliance (0.5-2.0 mL/cmH₂O), airway leak (0 to >45%), and apparatus dead space (5.5-9.1 mL) during pressure-controlled ventilation while alveolar carbon dioxide was held constant at 40 mmHg. Regression and receiver operating characteristic analyses were used to identify factors associated with reliable ETCO₂ measurement, defined as ETCO₂ ≥ 33.26 mmHg (≈83% of 40 mmHg).

Measurement reliability improved with increasing compliance, particularly under higher leak and larger dead space. Reliable ETCO₂ measurements were best predicted by expiratory tidal volume >12.6-14.0 mL (AUC 0.927-0.931) and an expiratory tidal volume-to-dead-space ratio >1.82 (AUC 0.984).

Reliable end-tidal carbon dioxide measurement depends on compliance, leak, and dead space; minimizing apparatus dead space and accounting for leak are essential, especially when expiratory tidal volume is small relative to dead space.

This study quantifies how lung compliance, airway leak, and dead space interact to determine ETCO₂ measurement reliability during neonatal ventilation. It clarifies measurement-related mechanisms that contribute to discrepancies between ETCO₂ and PaCO₂ in preterm infants. These findings can guide improvements in capnography technology and more individualized ventilator management in NICU settings.