THE INSPIRATORY: EXPIRATORY TIME (I:E) DURING HIGH FREQUENCY JET VENTILATION (HFJV) OF AN RDS MODEL

Abstract

HFJV, unlike high frequency oscillation, relies on passive elastic properties of the lung for exhalation. I:E can be adjusted to allow time for exhalation and prevent inadvertent PEEP. To determine which I:E affords maximal cardiopulmonary function we varied I:E from 1:1 to 1:5 at 600 BPM and measured PaO₂, PaCO₂, calculated alveolar-arterial O₂ differences (AaDO₂) and estimated systemic blood flow (Q) using Fick's principle (assuming constant oxygen consumption) in surfactant depleted cats (lungs lavaged 6 times). Mean airway pressure (MAP) was held constant at 6 cm H₂O, inspiratory pressure was 9 to 10 cm H₂O, PEEP 4 cm H₂O, and FiO₂ 1.0. Results (mean±SE) show highest PaO₂ and PaCO₂, and lowest AaDO₂ and Q were at 1:1. PaO₂ increased as ratios changed from 1:3 to 1:5 (p<0.01). It is interesting that oxygenation varied even though MAP, rate and FiO₂ were constant. Q at 1:5 was less than 1:4 (P<0.01). We conclude: the combination of best oxygenation and ventilation with least cardiovascular effects was obtained when an I:E of 1:4 was used.

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