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TECHNOLOGY, COMPUTING, AND SIMULATION

The Effect of a Bellows Leak in an Ohmeda 7810 Ventilator on Room Contamination, Inspired Oxygen, Airway Pressure, and Tidal Volume

Department of Anesthesiology, University of Florida, and the Evelyn F. and William L. McKnight Brain Institute of the University of Florida, Gainesville, Florida

Address correspondence to Samsun Lampotang, PhD, Department of Anesthesiology, P.O. Box 100254, Gainesville, FL 32610-0254. Address e-mail to slampotang{at}anest.ufl.edu.

We investigated the effect of a small bellows leak (bellows full at end-expiration) on inspired oxygen fraction (Fio₂), exhaled tidal volume (Vt), airway pressure, and room contamination in an oxygen-driven anesthesia ventilator (Ohmeda 7810, Madison, WI). CO₂ concentration at the ventilator exhalation valve, Fio₂, Vt, and airway pressure were measured (n = 3) while ventilating a CO₂-producing test lung at 8 breaths/min and an inspiratory/expiratory ratio of 1:2, with and without a bellows leak (4-mm-long tear). Set Vt was 400, 600, 800, and 1000 mL. Fresh gas flow (FGF) was 0.3 L/min O₂ and (a) 5.0 L/min air, (b) 2.0 L/min air, and (c) 0.2 L/min nitrogen. There was no clinical difference in Fio₂, Vt, PIP (peak inspiratory pressure) and PEEP (positive end-expiratory pressure), with and without a 4-mm bellows tear, at all FGFs and Vt settings. CO₂ at the ventilator exhalation valve was always nonzero with a bellows leak, indicating that CO₂-laden circuit gas was contaminating the drive gas via the bellows leak. A 4-mm bellows tear in an Ohmeda 7810 ventilator allows anesthetic gases to contaminate ambient air but does not cause clinically significant changes in Fio₂, exhaled Vt, PIP, or PEEP.