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Measurement of gas exchange in intensive care
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1989
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The new gas exchange monitor was evaluated in laboratory simulations and ICU patients. Laboratory simulations showed mean errors of 2–4 % for CO₂ and 4–27 % for O₂, with FiO₂, airway pressure, and PEEP having little effect and only a slight accuracy drop at the highest minute ventilation, and the device was found accurate for ICU gas exchange measurements. Crit Care Med 1989; 17:1041.
The performance of a new gas exchange monitor was assessed both in laboratory simulation and in ICU patients. Laboratory simulation using N2 and CO2 injections resulted in a mean error of 2 ± 2% in CO2 production (co2) and 4 ± 47c in oxygen consumption (o2) in respirator measurements (n = 55) and in a mean error of 3 ± 2% in co2 and 4 ± 27c in o2 in canopy measurements (n = 25). The mean error in RQ during ethanol burning was 2 ± 2% in respirator measurements (n = 45) and 1 ± 17c in canopy measurements. Fio2 had little effect on the accuracy of co2, whereas the accuracy on high rates of o2 (o2 = 400 ml/min) was reduced, when Fio2 increased: the error ranged from 1 ± 1% to 6 ± 17c, except at o2 400 ml/min during Fio2 0.8, where the error was 16 ± 37c. Neither peak airway pressure (+13 to +63 cm H2O) nor PEEP (0 to +20 cm H2O) had an effect on the accuracy. The highest level of minute ventilation studied (22.5 L/min) reduced the accuracy slightly (mean error of co2 4 ± 1% and o2 7 ± 27c). In patients during controlled mechanical ventilation, increasing Fio2 from 0.4 to 0.6 had no effect on the results. o2 was consistently higher by gas exchange than by the Fick principle: 16 ± 97c during controlled ventilation (n = 20), 21 ± 87c on synchronized intermittent mandatory ventilation (n = 10) and 25 ± 87c during spontaneous breathing. We conclude that the device proved to be accurate for gas exchange measurements in the ICU. (Crit Care Med 1989; 17:1041)