1997 OPEN FORUM Abstracts
TIDAL VOLUME DELIVERY OF A PROTOTYPE INFANT HFV DEVICE.
Kelvin D MacDonald, RRT, Peter B Wang, RRT, Kaiser Permanente Medical Center, Los Angeles. Dennis L Vinson, RCP. Childrens Hospital, Los Angeles.
Introduction: The Infrasonics Infant Star High Frequency Ventilator has a fixed inspiratory time of 18 msecs during HF ventilation. A new prototype model (950+) of the Infant Star features adjustable inspiratory times of 5 msec increments from 10 to 50 msec. We evaluated this new prototype to see the effect of varying inspiratory time on delivered Vt during HFV of a test lung. Using a precision (+/- 8%) system with a known underestimation bias (Monaco F, et al. 1993 AARC Conf. Open Forum), we sought to measure delivered Vt across a range of amplitude settings with different HFV inspiratory times. Methods: A prototype Nellcor-Puritan Bennett Infant Star 950+ was tested following calibration to factory standards. The device was attached to a 1.0 ml/cm H20 dynamic lung model (Michigan Inst., MI) with a 12 cm long, 3.5 mm I.D. ETT. A hot-wire anemometer ([NVM-I]Allied Medical, Riverside, CA) and pressure line were placed at the proximal wye and interfaced to a Novametrix Ventrak (Wallingford, CT) monitoring system. Frequency, Vt, and amplitude were captured and averaged for a three minute sample by IBM compatible PC. MAP was held at 30 cm H20, with the I.T. adjusted to 20, 35 and 45 msec for the prototype. Values for Vt were recorded at 10 Hz frequency, at the range of amplitude shown in the following tables:
950+ 12 cm 20 cm 40 cm 60 cm 80 cm
(20 msec) 0.8 cc 1.3 cc 2.0 cc 2.3 cc 3.3 cc
(35 msec) 1.4 cc 2.2 cc 3.6 cc 4.0 cc 5.8 cc
(45 msec) 2.0 cc 3.4 cc 5.2 cc 6.4 cc 9.1 cc
Vt as Insp. Time Increases @ 40 cm H2O Amp.
(See original for figure)
A plot of Vt with increasing I.T. shown above demonstrates the near linear (r2=.987) increase in Vt as I.T. is increased. This pattern was seen at all levels of amplitude tested. Conclusion: While measurements of delivered volume in our model cannot indicate clinical effectiveness, our experience suggests the prototype offers significant performance and range of Vt when compared to previous models of the Infant Star HFV. Further development and clinical trials seem warranted.