Effective Tidal Volume for Normocapnia in Very-Low-Birth-Weight Infants Using High-Frequency Oscillatory Ventilation

Abstract

PURPOSE: Removal of CO(2) is much efficient during high-frequency oscillatory ventilation (HFOV) for preterm infants. However, an optimal carbon dioxide diffusion coefficient (DCO(2)) and tidal volume (VT) have not yet been established due to much individual variance. This study aimed to analyze DCO(2) values, VT, and minute volume in very-low-birth-weight (VLBW) infants using HFOV and correlates with plasma CO(2) (pCO(2)). MATERIALS AND METHODS: Daily respiratory mechanics and ventilator settings from twenty VLBW infants and their two hundred seventeen results of blood gas analysis were collected. Patients were treated with the Drager Babylog VN500 ventilator (Dragerwerk Ag & Co.) in HFOV mode. The normocapnia was indicated as pCO(2) ranging from 45 mm Hg to 55 mm Hg. RESULTS: The measured VT was 1.7 mL/kg, minute volume was 0.7 mL/kg, and DCO(2) was 43.5 mL(2)/s. Mean results of the blood gas test were as follows: pH, 7.31; pCO(2), 52.6 mm Hg; and SpO(2), 90.5%. In normocapnic state, the mean VT was significantly higher than in hypercapnic state (2.1+/-0.5 mL/kg vs. 1.6+/-0.3 mL/kg), and the mean DCO(2) showed significant difference (68.4+/-32.7 mL(2)/s vs. 32.4+/-15.7 mL(2)/s). The DCO(2) was significantly correlated with the pCO(2) (p=0.024). In the receiver operating curve analysis, the estimated optimal cut-off point to predict the remaining normocapnic status was a VT of 1.75 mL/kg (sensitivity 73%, specificity 80%). CONCLUSION: In VLBW infants treated with HFOV, VT of 1.75 mL/kg is recommended for maintaining proper ventilation.