Bench evaluation of the Servo2 Oxygen-Control System

We evaluated the ability of a servo oxygen-control system (SS) to maintain oxygen concentration, or [O2], and carbon dioxide concentration, or [CO2], in an incubator within a narrow range while the percentage of O2 and CO2 and flow of gas mixtures supplied to the incubator were varied. MATERIALS & METHODS: To simulate high inspiratory flow and O2 demands, we suctioned gas from the incubator through a catheter continuously at 5 L/min. During suctioning, a respiratory mass spectrometer (MS) was used to sample [O2] at 48 equally spaced points at 3 heights within the incubator with the SS O2 control set, in turn, at 24, 35, 55, and 75%. To test CO2% at these oxygen concentrations, a dry mixture of 4.84% CO2 and 95.16% O2 was insufflated into the incubator at 1.0 L/min with the suction pump off while CO2% was sampled by MS at each sampling point. Suction, insufflation, and SS flows were measured by a pneumotachometer. RESULTS: With the incubator portholes closed, the O2% in the incubator did not differ from SS set values more than 1.1% (ie, difference in actual readings) at any sampling point. Similar results were obtained during the patient-care simulation when the rear port iris diaphragms were used. Drops in [O2] and restoration times for [O2] were unacceptable when front ports (without diaphragms) were used. No increase in CO2% above atmospheric baseline (0.03%) was observed during the insufflation of 4.84% CO2 into the incubator. CONCLUSIONS: Because our simulations were designed to mimic extreme clinical conditions, we believe that SS adequately controlled gas concentrations. [Respir Care 1996;41(8):724-727]