VALIDATION OF A SYSTEM FOR MEASUREMENT OF METABOLIC GAS EXCHANGE DURING ANAESTHESIA WITH CONTROLLED VENTILATION IN AN OXYGEN CONSUMING LUNG MODEL

An oxygen consuming lung model was used for evaluation and validationof a technique for metabolic gas exchange measurements duringcontrolled ventilation. The technique comprised a Servo 900C ventilator (Siemens) and separate oxygen and carbon dioxideanalysers (Beck-man). Measurements of oxygen consumption andcarbon dioxide production were made either by measuring inspiredand expired ventilation and gas fractions in these volumes orby measuring gas fractions and calculating expired ventilationfrom inspired by transformation (Haldane). Irrespective of theFl_O2, measured values correlated well with lung model settings:measured values were within ±2% of simulated. When Haldanetransformation was used with an Fl_O2 of 0.5 there was a significantunderestimation of oxygen consumption. Carbon dioxide productionvalues correlated well irrespective of the Fl_O2 used or methodof measurement of ventilation volume. Metabolic gas exchangemeasurements by measuring both inspired and expired ventilationvolumes may be used when inert gases are not in equilibrium,for example during nitrous oxide anaesthesia.