Humidification Performance of 48 Passive Airway Humidifiers François Lellouche, MD, PhD, Solenne Taillé, Eng, Frédéric Lefrançois, Eng, Nicolas Deye, MD, MSc, Salvatore Maurizio Maggiore, MD, PhD, Philippe Jouvet, MD, PhD, Jean-Damien Ricard, MD, PhD, Bruno Fumagalli, Eng, Laurent Brochard, MD  CHEST  Volume 135, Issue 2, Pages 276-286 (February 2009) DOI: 10.1378/chest.08-0679 Copyright © 2009 The American College of Chest Physicians Terms and Conditions

Figure 1 Hygrometric bench test apparatus used to measure the humidification performances of HMEs and antibacterial filters. A ventilator delivered controlled cycles (respiratory rate of 20 breaths/min with a tidal volume of 500 mL and a positive end-expiratory pressure of 5 cm H2O). A heated humidifier (MR 730) was connected to the expiratory limb of the model and was set to deliver gases with a water content of 35 mg H2O/L at the Y-piece. A circuit with heated wire was used after the humidification chamber. The room temperature was kept constant between 24.5°C and 25.5°C. CHEST 2009 135, 276-286DOI: (10.1378/chest.08-0679) Copyright © 2009 The American College of Chest Physicians Terms and Conditions

Figure 2 Inspired AH values obtained using the bench test apparatus compared to manufacturer data when available (29 devices). Results of the hydrophobic HME Pall BB2215 are also displayed. The asterisks indicate the devices that are proposed as antimicrobial filters. The numbering corresponds to Tables 1 and 2. CHEST 2009 135, 276-286DOI: (10.1378/chest.08-0679) Copyright © 2009 The American College of Chest Physicians Terms and Conditions

Figure 3 Humidity efficiency of the 48 devices tested calculated using the following formula: humidity efficiency (%) = (inspired AH/expired AH) × 100. Minimum and maximum efficiencies are indicated. CHEST 2009 135, 276-286DOI: (10.1378/chest.08-0679) Copyright © 2009 The American College of Chest Physicians Terms and Conditions

Figure 4 Frequency of endotracheal tube occlusions reported in the literature6–10,17,38–43,45–48,53–55 compared to the AH delivered by the HMEs measured using the bench test apparatus (Table 1). One study (circle) is an outlier56 with no endotracheal occlusions despite very poor humidification. However, this study56 only included 12 patients, which is not enough to reach a conclusion about the safety of the devices tested. A hydrophobic HME (Pall BB2215), which delivered a measured AH of 21.8 ± 1.5 mg H2O/L in the present study, has been associated with high rates of endotracheal tube occlusions in five previously published studies6–10 (Table 1). A number of studies are represented by gray dots to make them stand out. The sizes of the dots are proportional to the number of patients in the studies. CHEST 2009 135, 276-286DOI: (10.1378/chest.08-0679) Copyright © 2009 The American College of Chest Physicians Terms and Conditions