1995 OPEN FORUM Abstracts
NITRIC OXIDE AND THE MEASUREMENT OF METABOLICS WITH A PURITAN-BENNETT 7250 METABOLIC MONITOR
F Wayne Johnson RCP CRTT RPFT RCPT, K Knaus Kinninger RCP RPFT Kathy Jacobson RDA, John Newhart RCP CRTT, David Burns MD, UC-San Diego Medical Center, San Diego California
Introduction: In the mechanically ventilated critically ill patients, the use of indirect calorimetry for assessing energy expenditure, measure of substrate utilization (Stephen, NCP, 92; 7:207) and independent VO2 measurements for O2 uptake and O2 demand have been suggested (Ronco, ARRD, 91;143:1267). Recent reports of Inhaled Nitric Oxide (INO) as a potent dilator of vascular smooth muscle have demonstrated its usefulness in managing critically ill patients (Rossaint, N Engl J Med, 1993; 328:399). In the laboratory simulations during mechanical ventilation, we examined whether delivered INO and FIO2 influence the accuracy of the measurement of VO2/VCO2 with a open circuit metabolic monitor (PB7250, Puritan-Bennett, Carlsbad CA).
Methods: The simulation of VO2/VCO2 was achieved by the N2/CO2 infusion technique with a constructed lung model (Damask, Anesth., 1982, 57:213,). Delivery of INO utlized the technique where NO and N2 were blended with additional N2 (Channick, Chest 94;105:1842). Using a prototype stainless steel blender (Bird Corp., Palm Springs, CA). A chemiluminescence analyzer ( API Inc., San Diego, CA) was used to continuously measure the delivered NO and NO2. Exhaled gas was scavenged from the exhalation port. A PB7200ae ventilator and 7250 Metabolic Monitor accessory were utilized in a CMV mode of ventilation; ramp waveform; peak flow of 60 L/min; Vt .700 L; f 18; PEEP 0 cm H_2O; I/E ratio 1:1.6 and FIO2 of .21, .40, .60, .80. At each level of FIO2 for comparison purposes VO2/VCO2 simulations at .300 L/min were made with INO of 20ppm and without INO.
Results: The comparison of VO2/VCO2 measurements with and without delivered INO are presented in the table. Across all measurement levels the mean difference between methods (Bias) and the standard deviation of the difference (Precision) were determined to show agreement between data sets (Bland, Lancet, 1986; Feb:307-310).
Conclusions: Over a wide range of FIO2 levels, VO2/VCO2 values obtained using the PB7250 Metabolic Monitor were comaparable and within accetable limits to measurements with and without INO delivery. Our data suggests INO of< = 20 ppm has no affect on the performance of open circuit metabolic monitors.