Performance of the Uni-Vent Eagle™ Model 754 ventilator under hyperbaric conditions

Critically ill patients needing mechanical ventilation may require hyperbaric oxygen therapy. Some institutions still use ventilators that were available prior to the advent of hyperbaric-specific units, such as the Uni-Vent Eagle™ Model model 754. Here we examine the performance of the Uni-Vent model 754 under hyperbaric conditions and investigate concerns of an oxygen leak in the ventilator housing, which poses a fire risk. We studied the ventilator at 1.0, 2.4 and 2.8 ATA in assist control mode using a Michigan test lung and a variety of tidal volumes and respiratory rates. We recorded the delivered volumes, peak pressures, and oxygen percentages within the hyperbaric chamber at 2.4 and 2.8 ATA and within the ventilator housing. At those pressures the ventilator delivered approximately 25% less volume than at 1.0 ATA. We observed breath stacking at high respiratory rates, but this was blunted at both 2.4 and 2.8 ATA. Oxygen levels did not rise in the housing during our investigation. In addition, we fit a linear regression to the data comparing set tidal volumes and delivered tidal volumes in order to model the changes observed. Hyperbaric conditions caused decreased delivered tidal volumes in a depth-dependent fashion, and oxygen levels within the housing did not rise. The Uni-Vent Eagle model 754 performed safely and effectively at depth but requires spirometry to correctly program desired ventilator settings.