Bench Evaluation of the Sedaconda Inhaled Sedation Device: Hygrometric Properties and Device Resistance

Background: The Sedaconda Anesthetic Conserving Device (ACD-S) is used for inhaled sedation in intubated patients and has passive humidification properties linked to the carbon material. However, limited evaluations of the hygrometric performance are available. The main aim of the study was to assess the humidification performance of this device with different ventilator settings and ambient temperatures. Methods: We assessed hygrometry of inspiratory gases and resistance of the Sedaconda ACD-S using a bench test. Hygrometric measurements were performed with 5 min ventilations from 4.8 to 18 L/min (at constant ambient temperature: 25 ± 1°C) and with 3 ambient temperatures, 22-24°C, 25 ± 1°C, and 28-30°C (at constant minute ventilation: 10 L/min). Simulation of physiologic expiratory gases with an absolute humidity of 35 mg H₂O/L was used for main measurements. Some measurements were made with expiratory humidity of 27.5 mg H₂O/L which corresponds to what is found in patients with moderate hypothermia. Three hygrometric measurements using the psychrometric method were performed for each tested condition. Device resistance was evaluated before utilization and after 96 h on the humidified bench and compared with a paper- and foam-based heat and moisture exchangers (HME) with similar dead spaces. Results: In tested conditions, mean humidity output was 29.8 ± 1.3 mg H₂O/L. We found slightly lower humidity output at low versus high minute ventilation (respectively 28.0 ± 0.3 vs 30.6 ± 0.3, P < .001) and lowest versus highest ambient temperature (29.6 ± 0.3 vs 31.0 ± 0.2 mg H₂O/L, P = .02). These differences are probably not clinically important. We found a linear relationship between expiratory and inspiratory humidity (R² = 0.98, P < .001). Resistance of the tested device was higher, in comparison with paper- and foam-based HMEs, and increased slightly after 96 h of use on the bench. Conclusions: The Sedaconda ACD-S is a high-performance passive humidifier device, within all tested conditions of minute ventilation, tidal volume, and ambient temperature. Resistance was slightly higher compared with HMEs with similar dead space and different materials.