Carbon dioxide clearance using bubble CPAP with superimposed high-frequency oscillations in a premature infant lung model with abnormal lung mechanics

Abstract

Background: High-frequency (HF) oscillatory ventilation has been shown to improve carbon dioxide (CO₂ ) clearance in premature infants. In a previous in vitro lung model with normal lung mechanics we demonstrated significantly improved CO₂ washout by HF oscillation of bubble continuous positive airway pressure (BCPAP).

Objective: To examine CO₂ clearance in a premature infant lung model with abnormal lung mechanics via measurement of end-tidal CO₂ levels (EtCO₂ ) while connected to HF oscillated BCPAP.

Design and methods: A 40 mL premature infant lung model with either: normal lung mechanics (NLM): compliance 1.0 mL/cm H₂ O, airway resistance 56 cm H₂ O/(L/s); or abnormal lung mechanics (ALM): compliance 0.5 mL/cm H₂ O, airway resistance 136 cm H₂ O/(L/s), was connected to BCPAP with HF oscillation at either 4, 6, 8, 10, or 12 Hz. EtCO₂ was measured at BCPAPs of 4, 6, and 8 cm H₂ O and respiratory rates (RR) of 40, 60, and 80 breaths/min and 6 mL tidal volume.

Results: HF oscillation decreased EtCO₂ levels at all BCPAPs, RRs, and oscillation frequencies for both lung models. Overall mean ± SD EtCO₂ levels decreased (P < .001) from nonoscillated baseline by 19.3 ± 10.2% for NLM vs 14.1 ± 8.8% for ALM. CO₂ clearance improved for both lung models (P < .001) as a function of oscillation frequency and RR with greatest effectiveness at 40 to 60 breaths/min and HF at 8 to 12 Hz.

Conclusions: In this in vitro premature infant lung model, HF oscillation of BCPAP was associated with improved CO₂ clearance as compared with nonoscillated BCPAP for both NLM and ALM. The significant improvement in CO₂ clearance in an abnormal lung environment is an important step towards clinical testing of this novel respiratory support modality.

Keywords: CO2 clearance; airway resistance; end-tidal carbon dioxide; lung compliance; noninvasive ventilation.