Abstract 1862 Poster Session I, Saturday, 5/1 (poster 21)

In animals with normally compliant lungs, high frequency oscillatory ventilation (HFOV) achieves effective ventilation with low tidal volumes (Vt) while generating small pressure fluctuations in the alveolar spaces (ΔPa). We asked if the mechanical parameters of the neonatal respiratory system influence the magnitude of Vt and ΔPa during HFOV. Methods: A 3.1 L glass flask was connected to a 3.0-mm ID ETT. Compliance (C) was varied between 0.1 and 2.1 mL/cmH2O by filing the flask with known volumes of water. Ventilator amplitude were set to deliver 4.8 mL Vt [or highest achievable Vt in the Babylog 8000 (BL8000)] at C=0.4 mL/cmH2O. Pressure within the model lung (ΔPa) was measured using an MP15 transducer (Micron, CA). Vt was calculated from ΔPa using the adiabatic gas equation. The effect of C on Vt and ΔPa was evaluated at 15 Hz in 4 ventilators: 1) SensorMedics 3100 (SM3100); 2) Humming V (HUMV), Infant Star 950+ (IS950+) and the BL8000. In the SM3100, additional measurements were performed at 5 Hz & 10 Hz, and at 15 Hz using a 2.5mm & 3.5 mm ID ETT. Results: Vt ↑ while ΔPa ↓ with increasing C (see figure).

Figure 1
figure 1

Dependance of Vt and PA on compliance for the SM3100

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The % increase in Vt from C=0.1 to C=2.1 mL/cmH2O: 1) varied between ventilators (SM3100 172 %, HUMV 112 %, IS950+ 115 %, and BL8000 130 %); in the SM3100 2) decreased with ↑ frequency (5Hz 356 %, 10 Hz 244 %, 15 Hz 172 %); and 3) increased with ↑ ETT ID (2.5-mm 154 %, 3.0-mm 172 %, 3.5-mm 218 %). Conclusions: During HFOV in neonatal respiratory disease, the dependence of Vt and ΔPa on C is influenced by the specific ventilator employed, oscillatory frequency and the ETT ID. Despite effective low Vt ventilation, the use of HFOV to ventilate the poorly compliant premature lung may create ΔPa that approximate those observed during conventional ventilation.

Funding: Financial Markets Foundation for Children, Newborn Services, MMC. Equipment loans from SensorMedics Corporation, Infrasonics, Metran and Draegerwerk gratefully acknowledged