Hygrometric Performances of Heat and Moister Exchangers and Filters: Comparison of the Psychrometric Method and Manufacturers’ Data

Abstract

Background:

The gravimetric method (ISO) to evaluate humidity delivered by heat and moisture exchangers does not detect devices related with risks of endotracheal tube occlusion. Several studies showed significant differences between independent measurements of the humidity delivered by the HME and manufacturers data. Providing gas humidification greater than 28 mg H₂O/L (based on the psychrometric method) is mandatory for patients with prolonged intubation. The objective of this bench study was to evaluate the number of devices with adequate humidity delivery and to compare with manufacturers’ data.

Methods:

We tested on a bench, the hygrometric performances of 38 HME/HMEF and 28 filters. We used the psychrometric method to measure hygrometry at steady state, with expiratory humidity of 35 ± 0.5 mg H₂O/L simulated as previously described. For each condition, 3 hygrometric measurements were performed with similar conditions for ambient air temperature 25 ± 0.5°C, and ventilator settings (frequency 20 breaths/min, tidal volume 500 mL, FIO₂ 0.21, PEEP 5 cm H₂O, square flow 60 L/min). We compared data obtained on bench with data provided by the manufacturers.

Results:

Forty seven percent of the HMEs (18/38) provide absolute humidity above 28 mg H₂O/L (Figure). As expected no filters provided humidity above this limit. The mean measured absolute humidity in the group of HME/HMEF and filters were 26.7 and 14.7 mg H₂O/L respectively (P < .01). For HMEs, mean humidity data provided by the manufacturers was 33.4 mg H₂O/L (P < .01 in comparison with humidity measured with the psychrometric method). The mean differences between measured humidity and data provided by the manufacturers for performing HMEs was 2.5 mg H₂O/L, while this difference was 7.7 mg H₂O/L for HME with performances below 28 mg H₂O/L with the psychrometric method (P < .01). The main results are presented in the figure. These results are preliminary.

Conclusions:

Few HMEs provided sufficient gas humidity and important differences were found in terms of humidification performances between HMEs and filters. Data provided by manufacturers obtained with gravimetric method frequently overestimate data found with the psychrometric method.

Absolute Humidity delivered at the Y-piece measured with the psychrometric method for HME (black bars) and filters (grey bars). The humidity of 28 mgH₂O/L (red hatched line) is considered a safe limit for prolonged mechanical ventilation. Abbreviations: AH: absolute humidity.List of devices with humidity delivered above 28 mgH₂O/L with the psychrometric method: 1- DAR Ref 352-5805, 2- Flexicare Ref 300-210-000, 3- Flexicare Ref 300-610-000, 4- Medisize Ref 300-100-000, 5- Drager Ref MP05800, 6- DAR Ref 354-5876, 7- DAR Ref 352-5877, 8- Flexicare Ref 038-41-355U, 9- Medisize Ref 300-600-000, 10- Flexicare Ref 300-200-000, 11- Medisize Ref HF55, 12- Drager Ref MP05730, 13- Drager Ref MP01800, 14- Flexicare Ref 300-605-000, 15- Flexicare Ref 300-600-000, 16- DAR Ref 352-5903, 17- Drager Ref MP05810, 18- Vincent medical Ref 51002873