The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

The Effects Of Airway Leak On Tidal Volume During Pressure Or Flow Controlled Ventilation Of The Neonate: A Model Study

Robert L. Chatburn RRT, Teresa Volsko RRT. Rainbow Babies & Childrens Hospital Cleveland, OH, St. Elizabeth's Hospital Medical Center, Youngstown, OH.

Leaks associated with uncuffed endotracheal tubes complicate mechanical ventilation of the neonate. The variable nature of leaks and the possibility of different modes of ventilation suggest an optimal strategy for stability of tidal volume. The purpose of this study was to evaluate the effect of leak on tidal volume during pressure or flow controlled ventilation (PCV or FCV). METHOD: We used a lung model consisting of an elastic bellows (compliance = 1 mL/cm H_2O) attached to a 3.0 ET tube with a 3-way stopcock. One port of the stopcock was attached to a fixed orifice leak (% leak = 19-34 % depending on ventilator settings). A Newport Wave ventilator in SIMV mode generated either constant inspiratory pressure (PCV) or constant inspiratory flow (FCV) at the same tidal volume. Inspired and expired volumes were measured with a BICORE CP-100 Neonatal monitor. Calibration was verified with a 100 mL syringe. The effect of leak on exhaled tidal volume (VE) was defined as:

SEE ORIGINAL GRAPH

Large (=15 mL) and small (=7 mL) tidal volumes were used along with long (0.8 s) and short (0.3 s) inspiratory times. Each combination was repeated twice (n=3). Differences in % VE were evaluated with unpaired t-tests.

Results: The figures below show mean ± SD.

SEE ORIGINAL GRAPH

The effect of leak was generally less with PCV because it generated a larger mean inspiratory pressure, CONCLUSION: An optimum strategy for dealing with intermittent airway leaks might be short inspiratory times and relatively large tidal volumes independent of mode. At small tidal volumes and long inspiratory times, ventilation should be more stable with PCV.

OF-95-078

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