Gas Exchange During Ventilator Treatment: a Validation of a Computerized Technique and its Comparison With the Douglas Bag Method

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Abstract
In recent years a number of commercial instruments for on-line gas exchange measurements was introduced. The Engstrome Metabolic Computer (EMC) was clinically validated as compared to the standard Douglas bag method for gas sampling and a Centronic Mass Spectrometer (CMS) for gas analysis. .ovrhdot.VO2 [O2 uptake], .ovrhdot.VCO2 and RQ [respiratory quotient] were simultaneously measured and calculated with both methods. Twenty individual gas exchange determinations were made at different tomes on 12 critically ill patients at the intensive care unit. There was a small but significant difference (P < 0.025) of 4.3% .+-. 8.4% (SD) between the 2 methods when they were used to measure .ovrhdot.VO2 (the EMC giving the lower value). The corresponding value of .ovrhdot.VCO2 was 2.4% .+-. 9.1% (SD), and RQ the difference was -1.98 .+-. 7.1% (SD). These differences are not significant at the 95% level of significance. Determinations of O2 during ventilator treatment with standard methods usually involve technical difficulties and are associated with errors of method around 10%. A probable error of .apprx. 8.5% for .ovrhdot.VO2 in clinical situations is indicated. Considering the difficulties involved in determinations of gas exchange, the EMC method seems to be a valuable technique with an accuracy within acceptable limits.