Deviations in Function of Mechanical Ventilators during Hyperbaric Compression

Abstract

BACKGROUND: Because little is known of the effects of increased pressure on some mechanical ventilators, we studied the effects of a hyperbaric environment on the function of 19 mechanical ventilators, 13 of which had not previously been studied. METHODS & MATERIALS: Tests were performed on one of each of the following 19 ventilators: Bio-Med 1C-2A, Bio-Med ET-3, Bio-Med MVP-10, and Bio-Med P-7; Babybird, IMVbird, and Urgencybird; Oxylog; Autovent 2000; Oh-meda Logic 07; pneuPac Model 2 and pneuPac PNS 106; Omni-Vent HBC; Hy-draulic Emerson; Monaghan 225; Oxford (Penlon Ltd); Bird Mark 10 and Mark 14; and Bennett PR-2. Each ventilator was placed inside a hyperbaric chamber and adjusted to a rate of approximately 10 breaths/min, tidal volume of 1000 mL, and an inspiratory time of 1-2 s. Chamber pressure was then increased and output of the ventilator settings measured. The ventilators were grouped for evaluation into three functional groups: pneumatic time-cycled, pneumatic pressure-cycled, and volume-cycled (piston or bellows). RESULTS: Function of the ventilators was consistent within each group, with some minor exceptions; however, function var-ied between groups. Under the conditions of our study, the Oxford was the only currently available machine able to maintain rate, tidal volume, and inspiratory time under hyperbaric compression. CONCLUSIONS: The choice of a mechanical ventilator for use in a hyperbaric environment should be made carefully. Ven-tilator function may deviate from set levels during compression. A mechanical ventilator specifically developed for the hyperbaric environment is needed.