Validation of a System for Measurement of Metabolic Gas Exchange During Anaesthesia With Controlled Ventilation in an Oxygen Consuming Lung Model

Abstract

An oxygen consuming lung model was used for evaluation and validation of a technique for metabolic gas exchange measurements during controlled ventilation. The technique comprised a Servo 900 C ventilator (Siemens) and separate oxygen and carbon dioxide analysers (Beckman). Measurements of oxygen consumption and carbon dioxide production were made either by measuring inspired and expired ventilation and gas fractions in these volumes or by measuring gas fractions and calculating expired ventilation from inspired by transformation (Haldane). Irrespective of the FIO2, measured values correlated well with lung model settings: measured values were within +/- 2% of simulated. When Haldane transformation was used with an FIO2 of 0.5 there was a significant underestimation of oxygen consumption. Carbon dioxide production values correlated well irrespective of the FIO2 used or method of measurement of ventilation volume. Metabolic gas exchange measurements by measuring both inspired and expired ventilation volumes may be used when inert gases are not in equilibrium, for example during nitrous oxide anaesthesia.

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients

“…The accuracy of the V˙CO 2 measurement by the NICO was studied in a mechanical lung model connected to a Servo 900 C ventilator (Siemens‐Elema) where CO 2 could be added in defined amounts (11). The respiratory frequency, minute ventilation, dead space, PEEP and inspiratory/expiratory time were varied at two levels of CO 2 in the system.…”

Monitoring functional residual capacity (FRC) by quantifying oxygen/carbon dioxide fluxes during a short apnea

“…To determine the FRC by the apnea procedure, step 1 was to determine oxygen consumption and the carbon dioxide production by indirect calorimetry as well as the inspiratory and expiratory tidal volumes (8, 9).…”

“…The lung model was fitted with adjustable CO 2 output and O 2 consumption, achieved by combustion of hydrogen in a mini‐Bunsen burner (8). Combustion took place in the single alveolus of the lung model where the carbon dioxide also was delivered via a precision electronic flow controller.…”

Limitations of nutrient intake. The effect of stressors: trauma, sepsis and multiple organ failure

“…Because of the problem with the high F I O 2 all the commercially available indirect calorimeters cease to give Limitations of nutrient intake IT Campbell reliable results at an F I O 2 much above 0.6 ± 0.7. There are a number of ways around this problem, such as measuring inspired and expired volumes separately (Svensson et al, 1990), although this is technically very dif®cult to do with a suf®cient degree of accuracy, or measuring VCO 2 and assuming a respiratory quotient; oxygen consumption and energy expenditure can then be calculated. Technically this is the simplest solution; it introduces an error, but this is unlikely to exceed 10% and is certainly better than not making the measurement at all.…”