A Novel, Simplified Ex Vivo Method for Measuring Water Exchange Performance of Heat and Moisture Exchangers for Tracheostomy Application

Abstract

BACKGROUND: Breathing through a tracheostomy results in insufficient warming and humidification of inspired air. This loss of air-conditioning can be partially compensated for with the application of a heat and moisture exchanger (HME) over the tracheostomy. In vitro (International Organization for Standardization [ISO] standard 9360 -2:2001) and in vivo measurements of the effects of an HME are complex and technically challenging. The aim of this study was to develop a simple method to measure the ex vivo HME performance comparable with previous in vitro and in vivo results. METHODS: HMEs were weighed at the end of inspiration and at the end of expiration at different breathing volumes. Four HMEs (Atos Medical, Hörby, Sweden) with known in vivo humidity and in vitro water loss values were tested. The associations between weight change, volume, and absolute humidity were determined using both linear and non-linear mixed effects models. RESULTS: The rating between the 4 HMEs by weighing correlated with previous intratracheal measurements (R 2 ‫؍‬ 0.98), and the ISO standard (R 2 ‫؍‬ 0.77). CONCLUSIONS: Assessment of the weight change between end of inhalation and end of exhalation is a valid and simple method of measuring the water exchange performance of an HME.

Ex Vivo Assessment and Validation of Water Exchange Performance of 23 Heat and Moisture Exchangers for Laryngectomized Patients

“…midity (AH insp ), and breathing volume were measured using ex vivo weighing as described previously. 21 In the test configuration ( Fig. 1), the HME was mounted on a T-tube containing a fast heated capacitive hygrometer, absolute humidity sensor with a response time of 0.1-0.2 s, 23 and a spirometer (MLT300 Flowhead, ADInstruments, Oxfordshire, United Kingdom).…”

“…21 A summary of the normalization formulas is given in Appendix 1 (see the supplementary materials at http:// www.rcjournal.com).…”

“…The association between AH insp and inspiratory breathing volume was determined using an exponential decay nonlinear least squares regression as described previously. 21 For the core weight experiments, weighted r 2 values were calculated using weighted Pearson correlations with inverse variances as weights. Aikake information criterion was used to compare the associations between inspirational absolute humidity and both wet and dry core weights in two weighted linear regressions.…”

“…[18][19][20] These issues were overcome with the recent development of an ex vivo method that enables measurement of water exchange performance of a variety of HMEs within a short timeframe, without the need to trouble patients, while still being universally feasible. 21 In this method, the weight of an HME is measured twice: once at the end of inspiration and once at the end of expiration. The weight difference between end inspiration and end expiration (as function of the breathing volume) represents the water exchange performance during the breathing cycle.…”

Assessment of Humidification Performance: Still No Easy Method!

“…13 HMEs are passive humidifiers: during exhalation, gas is saturated with water and heated to around 32-33°C, 14,15 water is retained on hydrophobic and/or hygroscopic elements of the HME, and during inhalation the water vapor is released into the inspired gas, so the HME gains and loses weight during breathing. Van den Boer et al postulated that this weight variation could be a simplified measure for HME performance, and they measured the HME weight and compared the results to measurements made to the ISO standard.…”