Background: Aeromedical transport of critically ill casualties requires continued safe operation of medical equipment at altitude. We evaluated performance of two ventilators in an altitude chamber.
Methods: Two ventilators used by the United States Air Force (USAF) Critical Care Air Transport Teams were operated in an altitude chamber at barometric pressure of 754 mm Hg, 657 mm Hg, 563 mm Hg, and 428 mm Hg simulating altitudes of sea level, 4,000, 8,000, and 15,000 feet. At each altitude ventilators were set to deliver three tidal volumes (VT) from 0.25 L to 1.0 L. Airway pressure, timing, flow, and volumes were measured every breath. Measured parameters included VT, positive end-expiratory pressure (PEEP), inspiratory time, expiratory time, inspiratory flow, peak inspiratory pressure, expiratory flow, and respiratory rate.
Results: The Impact 754 compensated for changes in altitude maintaining the set VT within 10% of the sea level VT. Tidal volume delivery of the 754 was less precise during operation of the compressor at an inspired oxygen concentration of 0.21. With each increase in altitude, the LTV VT increased. At 8,000 feet VT increased by 10% and at 15,000 feet VT increased by 30% (p<0.001). Respiratory rate was not affected by altitude with either device.
Conclusions: The Impact 754 compensates ventilator output to deliver the desired tidal volume regardless of changes in altitude and barometric pressure. The LTV-1000 does not compensate for changes in altitude resulting in delivery of increasing tidal volumes with falling barometric pressure. Clinicians should be aware of ventilator performance and ventilator limitations to provide safe and effective ventilation during transport.