The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

EVALUATION OF VOLUME DELIVERY IN THE PEDIATRIC SETTING FOR TWO DUAL CONTROL MODES (DCM) OF VENTILATION IN THE PRESENCE OF INCREASING ENDOTRACHEAL TUBE LEAK

Kenneth F. Watson MS RRT, Eman S. Al-Khadra MBBS, John E. Thompson RRT, John Arnold MD. Children's Hospital, Boston, MA

Background: We investigated the ability of two ventilators set to operate in a dual control mode (DCM) to maintain target tidal volumes in the face of increasing endotracheal tube leak.

Methods: We evaluated volume delivery of DCMs for two ventilators (Augmented Pressure Ventilation, Hamilton Galileo; Pressure Regulated Volume Control, Siemens Servo 300A) using a DB&M Products Infant Lung Simulator. Patient conditions were simulated by appropriately matching tidal volumes from 30 to 200 mL to endotracheal tube sizes from 3.5 to 5.5 mm ID. A lung/thorax compliance of 3 mL/cm H2O was maintained. An adjustable valve was placed distal to the endotracheal tube to simulate leaks. Leaks in 5 per cent increments from 10 to 50 per cent were created. A heated wire pneumotach was placed between the ventilator and the endotracheal tube connection to measure leak percentage. Delivered and exhaled tidal volumes and minute volumes proximal and distal to the leak were measured using a pressure differential pneumotach.

Results: We evaluated the actual value and percentage change in inspired and expired tidal volume and minute volume for each volume/weight, endotracheal tube size, and leak percentage for the two ventilators. P value was calculated for the decrease in expired minute volume measured distal to the leak at each leak increment. At delivered tidal volumes less than or equal to 60 mL, minute volume did not decrease significantly in either ventilator (P ³ 0.05) until leaks greater than or equal to 20 per cent were created. With delivered tidal volumes greater than 60 mL, minute volume did decrease significantly (P £ 0.05) at leak percentages greater than 20 per cent. Therefore, proportionally larger decreases in expired minute ventilation were noted at larger tidal volumes at a given leak increment. Decreases in minute volume were greater in the Servo 300 than in the Galileo.

Conclusions: The two ventilators that we evaluated do not fully compensate for endotracheal tube leaks in their dual control modes. Although the decrease in volume loss to the patient is statistically significant, further investigation into its clinical significance is warranted.

OF-99-106

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