Background Noninvasive high frequency oscillatory ventilation (nHFOV) has been applied through nasal prongs as a new respiratory technique in preterm neonates and has been found to reduce CO2, but it has never been studied in bigger infants. Its mechanical properties when applied through a face mask are not known.
Methods We modeled the application of face mask-NHFOV in infants using a pediatric mannequin connected to an active lung simulator (ASL5000). This was set mimicking the mechanical properties of a normal lung (Crs 1 mL/cmH2O/Kg; Raw: 40 cmH2O/L/sec; Pmus 6 cmH2O; rate: 40 breaths/min) in a male infant at 1 year, 8 Kg, 3rd percentile for age. NHFOV parameters were sequentially changed. Spontaneous tidal volume (sTv), oscillatory stroke volume (oTv) and oscillation amplitude (DeltaPdist) at the lung simulator were recorded. Oscillatory pressure ratio (OPR: DeltaPdist/DeltaP) and the theoretical ventilation during HFOV (DCO2=frequency x oTv2) were also calculated.
Results Mean oTv, OPR and DCO2 were 1.9±0.7 mL/Kg, 0.05±0.02 and 221±136 Hz x mL2/Kg, respectively. Significant correlations were found between OPR and oTv (r=0.48; p<0.001) and OPR and DCO2 (r= 0.47; p<0.001).oTv significantly correlates with sTv (r=0,885; p<0,001). At a multivariate regression OPR was the factor more strongly associated with oTv (st.β=0.88) and DCO2 (st.β=0.96; p<0.001).
Discussion NHFOV through face mask is feasible. Oscillation amplitude is dampened by the interface and may reach in the lung 11% of the set value.Nonetheless, in this model adequate Tv and DCO2 are reached and OPR was the factor more strongly influencing ventilation.
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