[Validation of the gas exchange monitoring function of the Engström Elvira respirator]. / Validierung der Gasaustausch Monitoringfunktion des Engström-Elvira-Beatmungsgeräts.

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)

Evaluation of methods for indirect calorimetry with a ventilated lung model.

A combined lung and ventilator model was built, validated and used to test commercial systems for indirect calorimetry. It simulates O2 uptake and CO2 excretion under ventilator treatment conditions. In the model inspiratory gases are diluted with N2 and CO2 to give the desired expiratory concentrations. Minute volume, FIO2, ventilatory pressure, VO2, VCO2 and consequently RQ can be altered to simulate the adult clinical situation. A selected respiratory pattern is maintained by the lung model. Equipment for indirect calorimetry can then be connected to it and the results compared. Reference values are derived from measurements with a mass spectrometer and a Godart spirometer. Three commercially available instruments (Beckman MMC, Horizon MMC and Engström MC) were evaluated with this system. The limits of agreement with the reference values under different conditions (FIO2 0.4-0.7, ventilatory pressure 0-50 cmH2O) were determined. Differences as high as 15% from the true values of VO2 and V CO2 were observed. The pattern of mechanical ventilation and the intrinsic properties of the analyzers in the equipment used for indirect calorimetry influence measurements to a significant extent.

[A method for the determination of O2-uptake and CO2-elimination from the respiratory gases in mechanically ventilated patients (author's transl)]. / Ein Verfahren zur Bestimmung von O2-Aufnahme und CO2-Abgabe aus den Atemgasen beim beatmeten Patienten.

A method for the assessment of O2-uptake and CO2-elimination from respiratory gases in mechanically ventilated patients is presented, the Beckman metabolic measurement cart. It was designed for exercise measurements. In patients under respirator treatment, there are problems resulting from the pressure sensitivity of the polarographic O2-electrode. Correct measurements of O2-uptake is possible if an inspired O2-concentration of 50 per cent is not exceeded.