The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

DURATION OF FLOW AND ACCURACY OF TIDAL VOLUME DELIVERY WHEN USING 'D' CYLINDERS AS THE MAIN GAS SOURCE FOR THE BIRD AVIAN TRANSPORT VENTILATOR.

JIMMY P. CREDO, RRT, RPFT and DAVID C. SHELLEDY, PhD, RRT, RPFT, The University of Health Science Center at San Antonio, San Antonio, Texas.

BACKGROUND: Ventilator dependent patients may be transported using small oxygen cylinders. Knowledge of the duration of flow available from the cylinder at a given minute ventilation is needed to assure that a sufficient amount of time is available during transport. Traditionally, a standardized formula has been used to estimate duration of available flow: D cylinder flow duration (min.) = [(0.16 x gauge pressure)/minute volume]). We sought to determine the actual duration of flow available when using "D" oxygen cylinders as a main gas source to power the Bird Avian Transport Ventilator (Bird Products Corp., Palm Springs, CA). The effect of decreasing cylinder pressure on delivered tidal volume was also evaluated. METHOD: Five Bird Avian Transport ventilators were used in the study. Functional checks as specified by the manufacturer were performed on each ventilator. The ventilators were connected to full "D" oxygen cylinders as the main gas source. Ventilator parameters were set as follows: V_{T} 800 ml, frequency 12 BPM, V_{E} 9.6 L/min, inspiratory flow 50 L/min. Each ventilator was run continuously until the cylinder was empty. This was repeated for a total of three trials per ventilator. For each 100 psig cylinder pressure change, the expired tidal volume was measured using a Wright Respirometer. Results: The mean duration of flow for the three trials for each of the five ventilators is listed below:

v1 v2 v3 v4 v5

Mean (SD) Exp. Vol. 805.35 852.81 829.47 875.26 840.87

(3.43) (7.01) (1.90) (2.93) (3.00)

Mean (SD) duration of 31.47 31.08 32.98 30.30 32.47

flow (min.) (1.91) (2.00) (0.51) (0.45) (1.51)

The mean duration of flow for all trials for the five ventilators was 32.10 minutes (SD 1.51 min). This compared to a calculated available flow of 36.67 minutes. The mean expired tidal volumes of the five ventilators was 834.89 ml (SD = 22.71). There was no drop in delivered tidal volume until the cylinder pressures were below 250 psig. Conclusions: The Bird Avian Transport Ventilators delivered consistent tidal volumes until cylinder pressure was less than 250 psig. Duration of available flow was from 4-6 minutes less than the estimate provided using a standard formula. Our study suggests that "D" oxygen cylinders can be use effectively with the Bird Avian Transport Ventilator to transport ventilator dependent patients. We recommend that cylinders be changed when the cylinder pressure drops to approximately 250 psig to insure gas flow is not interrupted and to maintain adequate tidal volume delivery. We further recommend that the standard duration of flow calculation be used cautiously, as it may overestimate the time available for patient transport.

OF-97-090

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