[Validation of the gas exchange monitoring function of the Engström Elvira respirator]

Abstract

Gas exchange monitoring (GEM) has only recently become available for routine use on ventilated patients. Engström has introduced a new concept of integrated gas exchange monitoring within the Elvira respirator, optionally combined with an external CO2 monitor. The following paper describes a laboratory validation of a prototype of this device with regard to the influence of respiratory variables within their specified ranges: FIO2 0.2-0.6, FIO2-FEO2 (DFO2) 0.02-0.05, FECO2 0.02-0.05, VI 5-20 l/min, p 10-60 mbar, respiratory rate 7-29, VT 500-2,000 ml, inspiratory flow 25-90 l/min, relative humidity 5% and 55%. VO2 and VCO2 (100-700 ml/min) were simulated by gas dilution at a respiratory quotient of 1 using a 'bag-in-the-bottle' test lung for 48 test situations. Two reference measurements per test situation were carried out by mass spectrometry and wet-gas spirometry. The Elvira GEM function uses a self-calibrating fuel cell for FO2 detection, an external infrared CO2 monitor (Eliza) for FECO2 measurement, and differential pressure detection on a venturi principle for inspiratory flow measurement. VI measurement necessitates the use of the Haldane transformation for VO2 and VCO2 calculation. The VO2 (VCO2) repeatability coefficient (2 s) for the reference method was 5.6 (5.5) ml/min compared to 10.3 (10.35) ml/min for the GEM function. The mean relative methodical difference for VO2 (VCO2) was +19% (+4.1%) with limits of agreement (+/- 2 s) of +/- 13% (+/- 8.7%). The systematical difference for VCO2 as well as the variability within different test situations was in an acceptable range for clinical measurement.(ABSTRACT TRUNCATED AT 250 WORDS)