1995 OPEN FORUM Abstracts
EFFECT OF CHANGES IN ALTITUDE ON THE OPERATIONAL CHARACTERISTICS OF THE AMBU TRANSCARE PORTABLE VENTILATOR
Russell T. Reid RRT, Roxanne Eyler R.N., UC Davis Medical Center Sacramento, CA.
The use of portable mechanical ventilators during helicopter transport of the critically ill patient is common place. However, there is little data available regarding the performance of these ventilators under actual operating conditions. We sought to identify the effect changes in altitude had upon the set parameters on the Ambu Transcare (Ambu, INC.) pneumatically powered and controlled ventilator.
Methods: The Ambu Transcare was connected to two test lungs (Model 6006832 Siemens, Inc.), each with a capacity of 500 mls, wyed together. The ventilator pressure limiting device was set to the maximum value so as not to interfere with any changes in delivered volume or pressure. Baseline ventilator parameters were established at sea level (see table). Ventilator parameters were monitored and recorded, at 2000 feet increments, from sea level (baseline) to a maximum altitude of 10,000 feet. All measurements were performed in a MKB-117 aeromedical helicopter. Sufficient time was given between altitude changes for equipment stabilization. Five (5) repeat measurements were taken at each altitude. The following ventilator parameters were measured: cycles/min, expired tidal volume(VTe), inspiratory time(I. Time), peak inspiratory pressure(PIP), I:E ratio, and mean airway pressure(mean PAW) Expired tidal volume was measured using a Wright respirometer (Model Mark 8, fDE). All other ventilator parameters were measured with an electronic pressure transducer (Pneumogard 1230A, Novametrix, Inc.) which was zeroed at each new altitude. The Ambu Transcare was powered by and delivered 100% oxygen to the test lungs. All equipment was calibrated according to manufacturers recommendations.
Results: Data was analyzed using ANOVA. There were significant changes in all parameters at different altitudes (p < 0.01) with the exception of I:E ratio.
Parameters Sea Level 2000 Feet 4000 Feet 6000 Feet 8000 Feet 10,000
Cycles/min 12.0 (1.2) 15.3 (0.7)*14.3 (0.4)* 11.4 (1.8)* 11.1 (0.8)*11.4 (0.1)*
I. Time1.3 (0.0) 1.0 (0.1)* 1.2 (0.0)*1.4 (0.1)*1.4(0.0)* 1.3 (0.0)*
PIP (mean57.6 (2.3)*57.0 70.6 (2.3)81.4 (2.1)* 88.2 (1.6)*91.0 (0.7)*
±SD cm (13.8)*
VTe (mean1000 (0.0) 1030 1050 1234 1360 1444
±SD ml)(27.3)* (0.0)* (47.7)* (20.0)*(5.4)*
Mean PAW 12.2 (0.5) 13.9 (1.2)*15.8(0.3)*15.9 (1.6)*17.8 (0.2)* 20.4 (0.1)*
I:E Ration 1: 2.8 (0.0)1:2.8 (0.1) 1:2.6 (0.0) 1:2.8 (0.1)1:2.9 (0.0) 1:2.9 (0.0)
* significant difference between altitude groups p < 0.01
Experience: The authors have 10 years experience utilizing pneumatically powered and controlled mechanical ventilators during aeromedical transport. Conclusion: Clinically significant changes in set parameters may occur with pneumatically controlled ventilators in unpressurized aircraft cabins. We recommend monitoring mechanical ventilator parameters during flight with appropriate instrumentation. The Ambu Transcare ventilator's calibrated controls became inaccurate when the actual barometric pressure differed from the manufacturers calibration barometric pressure. The effect of altitude upon measuring instrumentation is unknown.