1995 OPEN FORUM Abstracts
CAPACITY OF THE SERVO2 OXYGEN CONTROL SYSTEM TO CONTROL FOR SET FIO2 AND FECO2--
Frank Dennison M.Ed RPFT RRT, D. Spencer Brudno, MD, David Lain PhD, Vladimir Kremenchugsky PhD, Medical College of Georgia, Augusta, Georgia.
Introduction: The purpose of our study was to use a mechanical model to evaluate the capacity of a newly manufactured instrument, the ServO2 Oxygen Control System (SS) designed for the Ohio Care Plus incubator, to maintain a set FiO2 and clear expired CO2 (FeCO2) during simulated clinical conditions.
Methods: For this evaluation, we constructed a metal grid within the incubator that provided a framework for measuring the concentration of oxygen (02%) and carbon dioxide (CO2%) at 16 coordinants per 3 height levels relevant to an infant's environment. To test for FiO2 maintenance during simulated high inspiratory flow and O2 demands, we used an Egnell Suction Pump to apply continuous suction at 5 L/min via a catheter placed in the incubator. During the suctioning, a mass spectrometer (MS) (Perkin-Elmer MGA 1100) was used to sample gas through a 3.0 m capillary at each coordinant with the SS FiO2 set at 0.24, 0.35, 0.55, and 0.75, respectively. An oxygen monitor (Ohmeda 5120) recorded incubator O2% in agreement with the SS set FiO2 throughout the study. To test for CO2 clearance, 4.84 % CO2 was insufflated into the incubator at 0.1 L/min. No suction was applied during the test for CO2 clearance. Suction and insufflation flow rates for the two procedures were measured by a Timeter RT-200 Calibration Analyzer. Descriptive statistics were used to analyze the data.
Results: Mean values (n=16) of the O2% maintained in the incubator at 3 height levels compared to set FiO2s are presented in Table 1. Difference in the MS measured O2% compared to the set FiO2 was never greater than 3.75% (e.g., 23.1 O2% versus the set 24.0 O2% (set FiO2 0.24) for any of the measurements. There was never an increase in CO2% in the incubator at any coordinant above atmospheric baseline (0.03%) during the insufflation procedure.
Table 1. Recorded O2% Values Compared to Set FiO2 at 3 Height Levels
Set FiO2=0.24 Set FiO2=0.35 Set FiO2=0.55 Set FiO2=0.75
Levels*L0 L10L25 L0 L10L25L0 L10L25L0 L10L25
Mean** 23.2 23.2 23.234.3 34.5 34.353.9 53.9 54.074.0 74.0 74.0
* At zero level (L0), gas was sampled at each coordinant at mattress level,
and at 10 cm (L10) and 25 cm (L25), respectively, above that level.
** Mean values and SD for the 16 coordinants measured at each level
Conclusions: According to research literature, normal O2 consumption and CO2 production for a large infant should approximate 33 mL/min (assumed 12 lb. infant and respiratory exchange ratio (VO2/VCO2) of 1.0 for calculations). Normal inspiratory flow demand for an infant approximates 2-3 L/min for 0.5 s per breath. To evaluate the system to insure that these demands could be met, our manual model evacuated (consumed) O2 at a rate of 1.2 to 3.75 L/min from the incubator's environment and inspiratory flow demand was continuous at 5 L/min. The simulated FeCO2 was 0.1 L/min, approxemately 3 times normal for a large infant. Thus, the simulated demands placed on the SS for FiO2 maintenance and CO2 clearance were very high. Though further research may be needed for humidification, temperature control, and noise production during operation of the system, our study supports its clinical use with respect to FiO2 maintenance and CO2 clearance. This study was supported by a grant from Ohmeda Inc. and two of the authors were Ohmeda Inc. empoyees.