The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

DETERMINING THE EFFECT OF FREQUENCY AND AMPLITUDE ON THE TIDAL VOLUME DELIVERED DURING HIGH FREQUENCY OSCILLATION

Khaled A. Sedeek MD, Muneyuki Takeuchi MD, Robert M. Kacmarek PhD RRT, Respiratory Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA

Background: HFO has been shown advantageous in the management of Infant Respiratory Distress Syndrome and has been proposed for use in Adult Respiratory Distress Syndrome. However, limited data on the effect of pressure amplitude (DP) and rate (Hz) on the tidal volumes delivered in adults is available. The aim of this study was to determine the tidal volume delivered at various rates and DP during HFO.

Methods: In six sheep (29±2 kg) severe lung injury was induced by repeated saline lung lavage until the PaO2 decreased to less than 100 mm Hg (65±14 mm Hg) during VC (FiO2 1.0, PEEP 5 cmH2O, VT 12 ml/kg and RR 15). After stabilization HFO was initiated at a MAP equal to the point of maximum curvature (PMC) on the expiratory limb of the P-V curve (27±2.4 cmH2O) (S Goddon: AJRCCM. 159:A77, 1999). VT at all combinations of rates 4, 6, 8, and 10 Hz, and pressure amplitudes of 30, 40, 50, and 60 cmH2O with an FiO2 of 1.0 and an Inspiratory time of 50% using the Sensomedics adult HFO was measured. Flow was measured by a pneumotachometer calibrated with a 400 ml/sec flow delivered by precision flowmeter (Brooks Instruments), Flow was amplified and digitized using a computerized graphics program (WINDAQ; Dataq Instruments Inc.) at 1000 Hz and recorded by using WINDAQ. Data was continuously recorded for one minute and three breaths were analyzed at each rate and DP using the WINDAQ playback system.

Results: Results (see table): VT was directly proportional to Amplitude (P<0.0001) and inversely proportional to the Frequency (P<0.0001). At 60 cm H2O DP and 4 Hz a 131±34 ml VT (» 4-5 ml/kg) was measured. Two way ANOVA showed no interaction between Frequency and Amplitude (all values are Mean ± S.D.).

AMPLITUDE FREQUENCY
10 Hz 8 Hz 6 Hz 4 Hz
60 cmH2O 35±11 ml 49±14 ml 75±21 ml 131±34 ml
50 cmH2O 30±10 ml 43±12 ml 64±16 ml 108±30 ml
40 cmH2O 24±9 ml 34±11 ml 52±13 ml 87±24 ml
30 cmH2O 18±6 ml 26±8 ml 40±10 ml 64±18 ml

Conclusion: At low rates and high DP in this model VTs approaching conventional mechanical ventilation are delivered during HFO.

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