Evaluation of a new operating room ventilator with volume-controlled ventilation: the Ohmeda 7900

Changes in fresh gas flow (FGF) during volume-controlled ventilation with the circle system have clinically important effects on the ventilatory variables of children. Current operating room ventilators allow a portion of the FGF to be added to the delivered tidal volume. The Ohmeda 7900 (Madison, WI) ventilator was designed to compensate for changes in FGF. We compared this ventilator with a standard ventilator, the Ohmeda 7000. Twenty patients (13-56 kg) undergoing dental or lower extremity surgery were studied. A side-by-side comparison of the two ventilators was performed using each patient as his or her own control. Beginning with the 7900 ventilator, FGF was set at 3.0 L/min, and the inspiratory to expiratory ratio was set at 1:2. Respiratory rate and tidal volume were adjusted to achieve an ETCO2 of 30-40 mm Hg. After a 10-min period of stabilization, inspired minute ventilation (VI), expired minute ventilation (VE), and ETCO2 were measured. FGF was then increased to 6.0 L/min, and the measurements were repeated after 10 min; FGF was then decreased to 1.5 L/min, and measurements were repeated after 10 min. The patient was then ventilated with an Ohmeda 7000 ventilator, and the sequence was repeated. The Ohmeda 7000 ventilator demonstrated significant changes in VI, VE, plateau pressure, and ETCO2, with changes in FGF (P = 0.0039-0.0001). The Ohmeda 7900 ventilator demonstrated compensation for changes in FGF; there were no significant changes in VI, VE, and ETCO2. We conclude that the Ohmeda 7900 ventilator provides stable ventilatory variables regardless of alterations in FGF (1.5-6.0 L/min).

In this study, we compared the effects of changing fresh gas flow on volume-controlled ventilation using two operating room ventilators (Ohmeda 7000 and Ohmeda 7900). The Ohmeda 7900, but not the Ohmeda 7000, provided stable ventilatory variables with fresh gas flows between 1.5 and 6.0 L/min.