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Review
, 9 (9), CD004711

Heat and Moisture Exchangers Versus Heated Humidifiers for Mechanically Ventilated Adults and Children

Affiliations
Review

Heat and Moisture Exchangers Versus Heated Humidifiers for Mechanically Ventilated Adults and Children

Donna Gillies et al. Cochrane Database Syst Rev.

Abstract

Background: Invasive ventilation is used to assist or replace breathing when a person is unable to breathe adequately on their own. Because the upper airway is bypassed during mechanical ventilation, the respiratory system is no longer able to warm and moisten inhaled gases, potentially causing additional breathing problems in people who already require assisted breathing. To prevent these problems, gases are artificially warmed and humidified. There are two main forms of humidification, heat and moisture exchangers (HME) or heated humidifiers (HH). Both are associated with potential benefits and advantages but it is unclear whether HME or HH are more effective in preventing some of the negative outcomes associated with mechanical ventilation. This review was originally published in 2010 and updated in 2017.

Objectives: To assess whether heat and moisture exchangers or heated humidifiers are more effective in preventing complications in people receiving invasive mechanical ventilation and to identify whether the age group of participants, length of humidification, type of HME, and ventilation delivered through a tracheostomy had an effect on these findings.

Search methods: We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase and CINAHL up to May 2017 to identify randomized controlled trials (RCTs) and reference lists of included studies and relevant reviews. There were no language limitations.

Selection criteria: We included RCTs comparing HMEs to HHs in adults and children receiving invasive ventilation. We included randomized cross-over studies.

Data collection and analysis: We assessed the quality of each study and extracted the relevant data. Where possible, we analysed data through meta-analysis. For dichotomous outcomes, we calculated the risk ratio (RR) and 95% confidence interval (95% CI). For continuous outcomes, we calculated the mean difference (MD) and 95% CI or standardized mean difference (SMD) and 95% CI for parallel studies. For cross-over trials, we calculated the MD and 95% CI using correlation estimates to correct for paired analyses. We aimed to conduct subgroup analyses based on the age group of participants, how long they received humidification, type of HME and whether ventilation was delivered through a tracheostomy. We also conducted sensitivity analysis to identify whether the quality of trials had an effect on meta-analytic findings.

Main results: We included 34 trials with 2848 participants; 26 studies were parallel-group design (2725 participants) and eight used a cross-over design (123 participants). Only three included studies reported data for infants or children. Two further studies (76 participants) are awaiting classification.There was no overall statistical difference in artificial airway occlusion (RR 1.59, 95% CI 0.60 to 4.19; participants = 2171; studies = 15; I2 = 54%), mortality (RR 1.03, 95% CI 0.89 to 1.20; participants = 1951; studies = 12; I2 = 0%) or pneumonia (RR 0.93, 95% CI 0.73 to 1.19; participants = 2251; studies = 13; I2 = 27%). There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia compared to HHs (RR 0.48, 95% CI 0.28 to 0.82; participants = 469; studies = 3; I2 = 0%)..The overall GRADE quality of evidence was low. Although the overall methodological risk of bias was generally unclear for selection and detection bias and low risk for follow-up, the selection of study participants who were considered suitable for HME and in some studies removing participants from the HME group made the findings of this review difficult to generalize.

Authors' conclusions: The available evidence suggests no difference between HMEs and HHs on the primary outcomes of airway blockages, pneumonia and mortality. However, the overall low quality of this evidence makes it difficult to be confident about these findings. Further research is needed to compare HMEs to HHs, particularly in paediatric and neonatal populations, but research is also needed to more effectively compare different types of HME to each other as well as different types of HH.

Conflict of interest statement

Donna Gillies: no conflict of interest.

David A Todd: no conflict of interest.

Jann P Foster: no conflict of interest.

Bisanth T Batuwitage: no conflict of interest.

Figures

Figure 1
Figure 1
Study flow diagram.
Figure 2
Figure 2
Methodological quality graph: review authors' judgements about each methodological quality item presented as percentages across all included studies.
Figure 3
Figure 3
Methodological quality summary: review authors' judgements about each methodological quality item for each included study.
Figure 4
Figure 4
Funnel plot of comparison: 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, outcome: 1.1 Artificial airway occlusion.
Figure 5
Figure 5
Funnel plot of comparison: 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, outcome: 1.2 Mortality.
Figure 6
Figure 6
Funnel plot of comparison: 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, outcome: 1.3 Pneumonia.
Analysis 1.1
Analysis 1.1
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 1 Artificial airway occlusion.
Analysis 1.2
Analysis 1.2
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 2 Mortality.
Analysis 1.3
Analysis 1.3
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 3 Pneumonia.
Analysis 1.4
Analysis 1.4
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 4 Atelectasis.
Analysis 1.5
Analysis 1.5
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 5 Tracheal aspirations (per day).
Analysis 1.6
Analysis 1.6
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 6 Saline instillations (number per day).
Analysis 1.7
Analysis 1.7
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 7 Change in body temperature (absolute data) (ºC).
Analysis 1.8
Analysis 1.8
Comparison 1 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ parallel studies, Outcome 8 Change in body temperature mean data) (ºC).
Analysis 2.1
Analysis 2.1
Comparison 2 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies, Outcome 1 PaO2 (mmHg).
Analysis 2.2
Analysis 2.2
Comparison 2 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies, Outcome 2 PaCO2 (mmHg).
Analysis 2.3
Analysis 2.3
Comparison 2 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies, Outcome 3 Breathing rate (breaths/minute).
Analysis 2.4
Analysis 2.4
Comparison 2 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies, Outcome 4 Tidal volume (L).
Analysis 2.5
Analysis 2.5
Comparison 2 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies, Outcome 5 Minute ventilation (L/minute).
Analysis 2.6
Analysis 2.6
Comparison 2 Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies, Outcome 6 Body temperature (ºC).
Analysis 3.1
Analysis 3.1
Comparison 3 Subgroup analysis ‐ children versus adults, Outcome 1 Artificial airway occlusion.
Analysis 3.2
Analysis 3.2
Comparison 3 Subgroup analysis ‐ children versus adults, Outcome 2 All‐cause mortality.
Analysis 4.1
Analysis 4.1
Comparison 4 Subgroup analysis ‐ length of ventilation, Outcome 1 Artificial airway occlusion.
Analysis 4.2
Analysis 4.2
Comparison 4 Subgroup analysis ‐ length of ventilation, Outcome 2 All‐cause mortality.
Analysis 4.3
Analysis 4.3
Comparison 4 Subgroup analysis ‐ length of ventilation, Outcome 3 Pneumonia.
Analysis 5.1
Analysis 5.1
Comparison 5 Subgroup analysis ‐ hygroscopic versus hydrophobic heat and moisture exchanger (HME), Outcome 1 Artificial airway occlusion.
Analysis 5.2
Analysis 5.2
Comparison 5 Subgroup analysis ‐ hygroscopic versus hydrophobic heat and moisture exchanger (HME), Outcome 2 All‐cause mortality.
Analysis 5.3
Analysis 5.3
Comparison 5 Subgroup analysis ‐ hygroscopic versus hydrophobic heat and moisture exchanger (HME), Outcome 3 Pneumonia.
Analysis 6.1
Analysis 6.1
Comparison 6 Heat and moisture exchanger (HME) with and without filters, Outcome 1 Artificial airway occlusion.
Analysis 6.2
Analysis 6.2
Comparison 6 Heat and moisture exchanger (HME) with and without filters, Outcome 2 All‐cause mortality.
Analysis 6.3
Analysis 6.3
Comparison 6 Heat and moisture exchanger (HME) with and without filters, Outcome 3 Pneumonia.
Analysis 7.1
Analysis 7.1
Comparison 7 Sensitivity analyses ‐ selection bias, Outcome 1 Mortality.
Analysis 7.2
Analysis 7.2
Comparison 7 Sensitivity analyses ‐ selection bias, Outcome 2 Pneumonia.
Analysis 8.1
Analysis 8.1
Comparison 8 Sensitivity analyses ‐ detection bias, Outcome 1 Artificial airway occlusion.
Analysis 8.2
Analysis 8.2
Comparison 8 Sensitivity analyses ‐ detection bias, Outcome 2 Pneumonia.

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