1995 OPEN FORUM Abstracts
PRESSURE VENTILATION DESPITE AIR LEAKS: QUANTITATION OF LEAK VOLUME AND MAINTENANCE OF TARGET PRESSURE.
Gary Gradwell, BS, RRT, Sharon Oliver, CRTT, Zenobia Black, CRTT, Lila Nasch, Shyni Thomas, RRT, Lisa Menegaz, CRTT, Sharlene Kennedy, CRTT, Deborah Epley, CRTT, Jerome Taylor, CRTT, Herbert Patrick, MD, Department of Respiratory Care, Thomas Jefferson University Hospital, Philadelphia, PA.
INTRODUCTION: Although pressure ventilation may be contraindicated with air leaks from the tracheal cuff or chest tubes, we were confronted with an ARDS patient on pressure ventilation with an air leak due to a pneumothorax and elected to maintain her on pressure control with the Bear 1000 ventilator. We chose to bench test the Bear 1000 in the pressure control mode using a simulated controlled leak to determine the ventilator's ability to maintain target pressure while we measured the accuracy of the added volume vs. the leak; we then correlated these results to the bedside situation. Our hypothesis was that the Bear 1000 would maintain the target pressure during inspiration via flow resulting in volume compensation for the leak.
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Methods: Bench test: A Bear 1000 Ventilator set at P/C of 30 cm./H_2O, 12 breaths/min. and a 3 second inspiratory time was connected to an Ohmeda Lung Simulator (resistance = 5). We measured the added volume on inspiration using a Bicore CP-100 Monitor, connected between the ventilator wye and the lung simulator. Five simulated controlled leaks were introduced at the lung simulator and each was measured by a Wallace and Tiernan Precision 65-150 Calibration Flowmeter. Bedside: We analyzed 11 different Bear 1000 graphic displays of the patient over a 5 day period for the added volume (phase 2) compared to the leak (phase 4).
Results:Bench test Bedside
tests, n 5 11
leak range, ml 150 - 60017 - 313
mean leak, ml370 77
mean added vol, ml322 67
accuracy (leak - added) / leak) %13 13
correlation coefficient .9998 .9891
Conclusions: The Bear 1000 ventilator 1) equally maintained both the target pressure on the bench test and the patient by delivering small bursts of flow resulting in 87% volume compensation; 2) graphic display accurately quantitated the volume of the patient's chest tube leak as phase 4 minus 13%.