IntroductionVolumetric capnography depicts volumetric capnograms [ie, the plot of expired carbon dioxide (CO2) over the tidal volume]. This bench study aimed to determine the reliability, accuracy, and precision of a novel infant simulator for volumetric capnography. This simulator would be clinically valuable for teaching purposes because it reflects the entire cardiopulmonary physiology within 1 breath.MethodsAn infant lung simulator was fed with CO2 supplied by a mass flow controller (VCO2-IN) and ventilated using standard settings. A volumetric capnograph was placed between the endotracheal tube and the ventilatory circuit. We simulated ventilated babies of different body weights (2, 2.5, 3, and 5 kg) with a VCO2 ranging from 12 to 30 mL/min. The correlation coefficient (r2), bias, coefficient of variation (CV = SD/x × 100), and precision (2 × CV) between the VCO2-IN and the elimination of CO2 recorded by the capnograph (VCO2-OUT) were calculated. The quality of the capnogram's waveforms was compared with real ones belonging to anesthetized infants using an 8-point scoring system, where 6 points or greater meant that the simulated capnogram showed good, 5 to 3 points acceptable, and less than 3 points an unacceptable shape.ResultsThe correlation between VCO2-IN and VCO2-OUT was r2 = 0.9953 (P < 0.001), with a bias of 0.16 (95% confidence intervals from 0.12 to 0.20) mL/min. The CV was 5% or less and the precision was 10% or less. All simulated capnograms showed similar shapes compared with real babies, scoring 6 points for 3 kg and 6.5 points for 2-, 2.5-, and 5-kg babies.ConclusionsThe simulator of volumetric capnograms was reliable, accurate, and precise for simulating the CO2 kinetics of ventilated infants.

BackgroundVolumetric capnography in healthy ventilated neonates showed deformed waveforms, which are supposedly due to technological limitations of flow and carbon dioxide sensors.AimsThis bench study analyzed the role of apparatus dead space on the shape of capnograms in simulated neonates with healthy lungs.MethodsWe simulated mechanical breaths in neonates of 2, 2.5, and 3 kg of body weight using a neonatal volumetric capnography simulator. The simulator was fed by a fixed amount of carbon dioxide of 6 mL/kg/min. Such simulator was ventilated in a volume control mode using fixed ventilatory settings with a tidal volume of 8 mL/kg and respiratory rates of 40, 35, and 30 breaths per minute for the 2, 2.5 and 3 kg neonates, respectively. We tested the above baseline ventilation with and without an additional apparatus dead space of 4 mL.ResultsSimulations showed that adding the apparatus dead space to baseline ventilation increased the amount of re‐inhaled carbon dioxide in all neonates: 0.16 ± 0.01 to 0.32 ± 0.03 mL (2 kg), 0.14 ± 0.02 to 0.39 ± 0.05 mL (2.5 kg), and 0.13 ± 0.01 to 0.36 ± 0.05 mL (3 kg); (p < .001). Apparatus dead space was computed as part of the airway dead space, and therefore, the ratio of airway dead space to tidal volume increased from 0.51 ± 0.04 to 0.68 ± 0.06, from 0.43 ± 0.04 to 0.62 ± 0.01 and from 0.38 ± 0.01 to 0.60 ± 0.02 in the 2, 2.5 and 3 kg simulated neonates, respectively (p < .001). Compared to baseline ventilation, adding apparatus dead space decreased the ratio of the volume of phase III to VT size from 31% to 11% (2 kg), from 40% to 16% (2.5 kg) and from 50% to 18% (3 kg); (p < .001).ConclusionsThe addition of a small apparatus dead space artificially deformed the volumetric capnograms in simulated neonates with healthy lungs.