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Background: High-flow nasal cannula therapy (HFNC) for neonate/infants can deliver up to 10 L/min of heated and humidified gas, and F IO 2 can be adjusted to between 0.21 and 1.0. With adults, humidification and actual F IO 2 are known to vary according to inspiratory and HFNC gas flow, tidal volume (V T ), and ambient temperature. There have been few studies focused on humidification and F IO 2 in HFNC settings for neonates/infants, so we performed a bench study to investigate the influence of gas flow, ambient temperature, and respiratory parameters on humidification and actual F IO 2 in a neonate/infant simulation., Methods: HFNC gas flow was set at 3, 5, and 7 L/min, and F IO 2 was set at 0.3, 0.5, and 0.7. Spontaneous breathing was simulated using a 2-bellows-in-a-box model of a neonate lung. Tests were conducted with V T settings of 20, 30, and 40 mL and breathing frequencies of 20 and 30 breaths/min. Inspiratory time was 0.8 s with decelerating flow waveform. The HFNC tube was placed in an incubator, which was either set at 37°C or turned off. Absolute humidity (AH) and actual F IO 2 were measured for 1 min using a hygrometer and an oxygen analyzer, and data for the final 3 breaths were extracted., Results: At all settings, when the incubator was turned on, AH was greater than when it was turned off ( P < .001). When the incubator was turned off, as gas flow increased, AH increased ( P < .001); however, V T did not affect AH ( P = .16). As gas flow increased, actual F IO 2 more closely corresponded to set F IO 2 . When gas flow was 3 L/min, measured F IO 2 decreased proportionally more at each F IO 2 setting increment ( P < .001)., Conclusions: AH was affected by ambient temperature and HFNC gas flow. Actual F IO 2 depended on V T when gas flow was 3 L/min., Competing Interests: The authors have disclosed no conflicts of interest., (Copyright © 2017 by Daedalus Enterprises.)

Background: High-flow nasal cannula (HFNC) therapy provides better humidification than conventional oxygen therapy. To allay loss of vapor as condensation, a servo-controlled heating wire is incorporated in the inspiratory tube, but condensation is not completely avoidable. We investigated factors that might affect condensation: thermal characteristics of the inspiratory tube, HFNC flow, and ambient temperature., Methods: We evaluated 2 types of HFNC tubes, SLH Flex 22-mm single tube and RT202. Both tubes were connected to a heated humidifier with water reservoir. HFNC flow was set at 20, 40, and 60 L/min, and FIO2 was set at 0.21. Air conditioning was used maintain ambient temperature at close to either 20 or 25°C. We weighed the tubes on a digital scale before (0 h) and at 3, 6, and 24 h after, turning on the heated humidifier, and calculated the amount of condensation by simple subtraction. The amount of distilled water used during 24 h was also recorded., Results: At 25°C, there was little condensation, but at 20°C and HFNC flow of 20, 40, and 60 L/min for 24 h, the amount of condensation with the SLH was 50.2 ± 10.7, 44.3 ± 17.7, and 56.6 ± 13.9 mg, and the amount with the RT202 was 96.0 ± 35.1, 72.8 ± 8.2, and 64.9 ± 0.8 mg. When ambient temperature was set to 20°C, condensation with the RT202 was statistically significantly greater than with the SLH at all flow settings (P < .001)., Conclusions: Ambient temperature statistically significantly influenced the amount of condensation in the tubes., (Copyright © 2016 by Daedalus Enterprises.)

Introduction: Delivering heated and humidified medical gas at 20-60 L/min, high-flow nasal cannula (HFNC) creates low levels of PEEP and ameliorates respiratory mechanics. It has become a common therapy for patients with respiratory failure. However, independent measurement of heat and humidity during HFNC and comparison of HFNC devices are lacking., Methods: We evaluated 2 HFNC (Airvo 2 and Optiflow system) devices. Each HFNC was connected to simulated external nares using the manufacturer's standard circuit. The Airvo 2 outlet-chamber temperature was set at 37°C. The Optiflow system incorporated an O2/air blender and a heated humidifier, which was set at 40°C/3. For both systems, HFNC flow was tested at 20, 40, and 50 L/min. Simulating spontaneous breathing using a mechanical ventilator and TTL test lung, we tested tidal volumes (VT) of 300, 500, and 700 mL, and breathing frequencies of 10 and 20 breaths/min. The TTL was connected to the simulated external nares with a standard ventilator circuit. To prevent condensation, the circuit was placed in an incubator maintained at 37°C. Small, medium, and large nasal prongs were tested. Absolute humidity (AH) of inspired gas was measured at the simulated external nares., Results: At 20, 40, and 50 L/min of flow, respective AH values for the Airvo 2 were 35.3 ± 2.0, 37.1 ± 2.2, and 37.6 ± 2.1 mg/L, and for the Optiflow system, 33.1 ± 1.5, 35.9 ± 1.7, and 36.2 ± 1.8 mg/L. AH was lower at 20 L/min of HFNC flow than at 40 and 50 L/min (P < .01). While AH remained constant at 40 and 50 L/min, at 20 L/min of HFNC flow, AH decreased as VT increased for both devices., Conclusions: During bench use of HFNC, AH increased with increasing HFNC flow. When the inspiratory flow of spontaneous breathing exceeded the HFNC flow, AH was influenced by VT. At all experimental settings, AH remained > 30 mg/L.

Background: Because noninvasive ventilation (NIV) delivers medical gas at high flow, inadequate humidification may cause oral dryness and patient discomfort. Heated humidification can be used during NIV, but little has been reported about the effects on the hygrometric conditions inside an oronasal mask and oral dryness during 24 hours on NIV., Methods: We measured absolute humidity (AH) inside oronasal masks on subjects with acute respiratory failure during 24 hours on NIV. A single-limb turbine ventilator and oronasal mask with an exhalation port were used for NIV. Oral moistness was evaluated using an oral moisture-checking device, and 3 times during the 24 hours the subjects subjectively scored the feeling of dryness on a 0-10 scale in which 10 was the most severe dryness., Results: Sixteen subjects were enrolled. The mean ± SD AH inside the mask was 30.0 ± 2.6 mg H2O/L (range 23.1-33.3 mg H2O/L). The median oral moistness was 19.2% (IQR 4.4-24.0%), and the median oral dryness score was 5.5 (IQR 4-7). AH and inspired gas leak correlated inversely, both within the subjects (r = -0.56, P < .001) and between the subjects (r = -0.58, P = .02). AH and oral moistness correlated within the subjects (r = 0.39, P = .04). Oral breathing was associated with reduced oral moistness (P = .001) and increased oral dryness score (P = .002)., Conclusions: AH varied among the subjects, and some complained of oral dryness even with heated humidifier. Oral breathing decreased oral moistness and worsened the feeling of dryness.

Background: Heat and moisture exchangers (HMEs) are commonly used for humidifying respiratory gases administered to mechanically ventilated patients. While they are also applied to tracheostomized patients with spontaneous breathing, their performance in this role has not yet been clarified. We carried out a bench study to investigate the effects of spontaneous breathing parameters and oxygen flow on the humidification performance of 11 HMEs., Methods: We evaluated the humidification provided by 11 HMEs for tracheostomized patients, and also by a system delivering high-flow CPAP, and an oxygen mask with nebulizer heater. Spontaneous breathing was simulated with a mechanical ventilator, lung model, and servo-controlled heated humidifier at tidal volumes of 300, 500, and 700 mL, and breathing frequencies of 10 and 20 breaths/min. Expired gas was warmed to 37°C. The high-flow CPAP system was set to deliver 15, 30, and 45 L/min. With the 8 HMEs that were equipped with ports to deliver oxygen, and with the high-flow CPAP system, measurements were taken when delivering 0 and 3 L/min of dry oxygen. After stabilization we measured the absolute humidity (AH) of inspired gas with a hygrometer., Results: AH differed among HMEs applied to tracheostomized patients with spontaneous breathing. For all the HMEs, as tidal volume increased, AH decreased. At 20 breaths/min, AH was higher than at 10 breaths/min. For all the HMEs, when oxygen was delivered, AH decreased to below 30 mg/L. With an oxygen mask and high-flow CPAP, at all settings, AH exceeded 30 mg/L., Conclusions: None of the HMEs provided adequate humidification when supplemental oxygen was added. In the ICU, caution is required when applying HME to tracheostomized patients with spontaneous breathing, especially when supplemental oxygen is required.

Purpose: Oral dryness is a common complication during noninvasive ventilation (NIV). We measured the oral dryness of patients and performed a bench study to investigate factors related to humidification during NIV., Materials and Methods: Patients were randomly assigned into 2 groups: medium (Med group) and maximum (Max group) heated humidifier (HH) settings. Oral moistness was measured using an oral moisture-checking device, and the feeling of oral dryness was evaluated using a 0 to 10 numerical rating scale (NRS) at 0, 12, and 24 hours from the beginning of NIV and at 12 and 24 hours after NIV was discontinued. A bench study was performed to assess the effects of positive end-expiratory pressure (PEEP), the fraction of inspired oxygen (F(I)O(2)), and air leaks on absolute humidity. We evaluated 3 HH settings: no HH, HH at the medium setting, and HH at the maximum setting. The temperature in the outlet chamber was 31°C to 32°C for the medium HH setting and 38°C to 41°C for the maximum HH setting., Results: In the clinical study, 12 patients were assigned to the Med group and 11 to the Max group. In the Med group, oral moistness decreased and NRS increased at 12 and 24 hours compared with 0 hours (P < .05). In the Max group, neither the oral moistness nor the NRS changed throughout the study period, whereas in the bench study, high F(I)O(2), high PEEP, and air leak decreased the absolute humidity for both HH settings (P < .01). However, it is not clear to what extent these factors affected the patients' oral dryness because the ranges of F(I)O(2) and PEEP were narrow., Conclusions: Oral dryness was a common problem in our patients. The HH setting significantly affected humidification and oral dryness during NIV., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Background: High-frequency oscillatory ventilation (HFOV) has recently been applied to acute respiratory distress syndrome patients. However, the issue of humidification during HFOV has not been investigated. In a bench study, we evaluated humidification during HFOV for adults to test if adequate humidification was achieved in 2 different HFOV systems., Material/methods: We tested 2 brands of adult HFOV ventilators, the R100 (Metran, Japan) and the 3100B (SensorMedics, CA), under identical bias flow. A heated humidifier consisting of porous hollow fiber (Hummax II, Metran) was set for the R100, and a passover-type heated humidifier (MR850, Fisher & Paykel) was set for the 3100B, while inspiratory heating wire was applied to both systems. Each ventilator was connected to a lung model in an incubator. Absolute humidity, relative humidity and temperature at the airway opening were measured using a hygrometer under a variety of ventilatory settings: 3 stroke volumes/amplitudes, 3 frequencies, and 2 mean airway pressures., Results: The R100 ventilator showed higher absolute humidity, higher relative humidity, and lower temperature than the 3100B. In the R100, as stroke volume and frequency increased, absolute humidity and temperature increased. In the 3100B, amplitude, frequency, and mean airway pressure minimally affected absolute humidity and temperature. Relative humidity was almost 100% in the R100, while it was 80.5±2.3% in the 3100B., Conclusions: Humidification during HFOV for adults was affected by stroke volume and frequency in the R100, but was not in the 3100B. Absolute humidity was above 33 mgH&#95;2 O/L in these 2 systems under a range of settings.

Background: High-frequency oscillation ventilation (HFOV) is an accepted ventilatory mode for acute respiratory failure in neonates. As conventional mechanical ventilation, inspiratory gas humidification is essential. However, humidification during HFOV has not been clarified. In this bench study, we evaluated humidification during HFOV in the open circumstance of ICU. Our hypothesis is that humidification during HFOV is affected by circuit design and ventilatory settings., Methods/materials: We connected a ventilator with HFOV mode to a neonatal lung model that was placed in an infant incubator set at 37 degrees C. We set a heated humidifier (Fisher & Paykel) to obtain 37 degrees C at the chamber outlet and 40 degrees C at the distal temperature probe. We measured absolute humidity and temperature at the Y-piece using a rapid-response hygrometer. We evaluated two types of ventilator circuit: a circuit with inner heating wire and another with embedded heating element. In addition, we evaluated three lengths of the inspiratory limb, three stroke volumes, three frequencies, and three mean airway pressures., Results: The circuit with embedded heating element provided significantly higher absolute humidity and temperature than one with inner heating wire. As an extended tube lacking a heating wire was shorter, absolute humidity and temperature became higher. In the circuit with inner heating wire, absolute humidity and temperature increased as stroke volume increased., Conclusion: Humidification during HFOV is affected by circuit design and ventilatory settings.

Background: In mechanically ventilated patients, we investigated how positioning the heat and moisture exchanger (HME) at different places on the ventilator circuit affected inspiratory gas humidification., Methods: Absolute humidity (AH) and temperature (TEMP) at the proximal end of endotracheal tube (ETT) were measured in ten mechanically ventilated patients. The HME was connected either directly proximal to the ETT (Site 1) or at before the circuit Y-piece (Site 2: distance from proximal end of ETT and Site 2 was about 19 cm) (Figure. 1). Two devices, Hygrobac S (Mallinckrodt Dar, Mirandola, Italy) and Thermovent HEPA (Smiths Medical International Ltd., Kent, UK) were tested. AH and TEMP were measured with a hygrometer (Moiscope, MERA Co., Ltd., Tokyo, Japan)., Results: Hygrobac S provided significantly higher AH and TEMP at both sites than Thermovent HEPA. Both Hygrobac S and with Thermovent HEPA provided significantly higher AH and TEMP when placed proximally to the ETT., Conclusion: Although placement proximal to the ETT improved both AH and TEMP in both HMEs tested, one HME performed better in the distal position than the other HME in the proximal position. We conclude the both the type and placement of HME can make a significant difference in maintaining AH and TEMP during adult ventilation.

Purpose: We hypothesized that expiratory tidal volume was underestimated, because a heat-moisture exchanger traps the expired vapor. We, therefore, designed patient and bench studies to investigate the accuracy of tidal volume monitoring., Methods: In a patient study, applying two humidifying systems (a heat-moisture exchanger and a heated humidifier) and two tidal volumes (12 and 6 ml x kg(-1)) with a Servo ventilator 300, we recorded the displayed expiratory tidal volume and thoracic volume displacement, measured by respiratory inductive plethysmography. Temperature, relative humidity, and absolute humidity were measured at the airway opening and at the end of the expiratory limb. Using a model lung, we also tested three different ventilators (Puritan-Bennett 7200ae, Evita 4, and Servo ventilator 300) to investigate whether the effects of the heat-moisture exchanger and the heated humidifier on monitored tidal volume varied according to the brand of ventilator., Results: With the use of the heat-moisture exchanger, the displayed expiratory tidal volume was significantly smaller, by 12%-14%, than that with the heated humidifier, although thoracic volume displacement was identical in the two systems. The temperature and absolute humidity at the end of the expiratory limb were significantly lower with the heat-moisture exchanger than with the heated humidifier. In the model lung study, we investigated the effects of different brands of ventilator on the expiratory tidal volume. A similar degree (8%-14%) of underestimation of tidal volume was observed with the heat-moisture exchanger, regardless of ventilator brand., Conclusion: Monitored expiratory tidal volume was underestimated by approximately 10%, when using a heat-moisture exchanger.