1995 OPEN FORUM Abstracts
VALIDATION OF FIO_2 STABILITY IN THE PURITAN BENNETT 7200AE VENTILATOR WITH THE 7250 METABOLIC MONITOR
K. Knaus Kinninger RCP RPFT, F. Wayne Johnson RCP CRTT RPFT RCPT, Kathy Jacobson RDA, David Burns MD, UC-San Diego Medical Center, San Diego California
Introduction: The delivery of a constant FIO2 by mechanical ventilation is essential for the accurate measurement of oxygen consumption (VO2) for indirect calorimetry measurements. Fluctuations in FIO2 of 0.005 can result in errors of 25% in measured VO2. The use of an airoxygen blender (Browning, Crit. Care, 1982;10:82) or mixing chamber (Johnson, Resp. Care, 1991;36(11):1274) (Branson, Aspen, 1992; Clin. Congress (95):480) in line on the inspiratory limb of the ventilator circuit, has been recommended as a method to stabilize fluctuations in the variability of the delivered FIO2. Our study examines the FIO2 stability of the 7200ae ventilator installed with the 7250 Metabolic Monitor accessory and software package which stabilizes the 7200ae delivered FIO2 (Puritan-Bennett, Carlsbad, CA).
Methods: We conducted four parallel experiments with a 7200ae ventilator, installed with a 7250 option, connected to a simulated lung model. Measurements of FIO2 were obtained from the distal outlet of the humidifier using a 1100A mass spectrometer (Perkin Elmer, Pasadena, CA).The mass spectrometer was calibrated prior to each use with a primary gravimetric standard calibration gas (Scott Medical Products, Plumsteadville, PA). Oxygen waveforms were sampled at 50 Hz by a computerized data acquisition system (Codas, Data Instru., Akron OH), digitized and stored on a microcomputer. The independent component in our study was the type of humidifier or device used in the inspiratory limb of the ventilator circuit. The dependent variable was the measured FIO2 fluctuations. In Method I, we used the 7200ae ventilator with wall air/oxygen gas source, bacterial filter, disposable circuit, and Cascade I humidifier. Method II, we exchanged the Cascade I with a SCT humidifier. Method III, the humidifier was eliminated from the circuit to replicate the use of a heat moisture exchanger (HME). Method IV, using the same ventilator circuit described in Method III an additional bacterial filter was placed in line on the inspiratory circuit. All methods were tested with 7200ae ventilator settings of CMV, ramp flow waveform, peak flow 60 L/min, PEEP 0 cm H_2O, Vt 1.000 L, f of 10, 14, 18 and FIO2 of .40, .60, and .80.
Results: The values shown in the table reflect actual fluctuations within and between each delivered breath. Inspired oxygen stability as defined is a fluctuation in FIO2 less than 0.002 (Browning, Crit. Care, 1982;10:82).
Methods: Cascade SCT HME HME/xtra Filter
Stability in FIO2: .0013 .0013.0033 .0019
Conclusions: The Puritan-Bennett 7200ae ventilator with enhanced software provides a stable FIO2 across (.21-.80 range) which eliminates the use of external or in line devices for indirect calorimetry measurements. However, when using a HME humidification system our data suggests the use of a mixing chamber type device such as a second inspiratory filter to provide a delivered FIO2 that is within acceptable clinical stability of< = .002 (Browning, Crit. Care, 1982;10:82). This will result in a error of measured VO2 of less than 7%.