Heat and moisture exchangers (HMEs) and heated humidifiers (HHs) in adult critically ill patients: a systematic review, meta-analysis and meta-regression of randomized controlled trials

Abstract

Background: The aims of this systematic review and meta-analysis of randomized controlled trials are to evaluate the effects of active heated humidifiers (HHs) and moisture exchangers (HMEs) in preventing artificial airway occlusion and pneumonia, and on mortality in adult critically ill patients. In addition, we planned to perform a meta-regression analysis to evaluate the relationship between the incidence of artificial airway occlusion, pneumonia and mortality and clinical features of adult critically ill patients.

Methods: Computerized databases were searched for randomized controlled trials (RCTs) comparing HHs and HMEs and reporting artificial airway occlusion, pneumonia and mortality as predefined outcomes. Relative risk (RR), 95% confidence interval for each outcome and I ² were estimated for each outcome. Furthermore, weighted random-effect meta-regression analysis was performed to test the relationship between the effect size on each considered outcome and covariates.

Results: Eighteen RCTs and 2442 adult critically ill patients were included in the analysis. The incidence of artificial airway occlusion (RR = 1.853; 95% CI 0.792-4.338), pneumonia (RR = 932; 95% CI 0.730-1.190) and mortality (RR = 1.023; 95% CI 0.878-1.192) were not different in patients treated with HMEs and HHs. However, in the subgroup analyses the incidence of airway occlusion was higher in HMEs compared with HHs with non-heated wire (RR = 3.776; 95% CI 1.560-9.143). According to the meta-regression, the effect size in the treatment group on artificial airway occlusion was influenced by the percentage of patients with pneumonia (β = -0.058; p = 0.027; favors HMEs in studies with high prevalence of pneumonia), and a trend was observed for an effect of the duration of mechanical ventilation (MV) (β = -0.108; p = 0.054; favors HMEs in studies with longer MV time).

Conclusions: In this meta-analysis we found no superiority of HMEs and HHs, in terms of artificial airway occlusion, pneumonia and mortality. A trend favoring HMEs was observed in studies including a high percentage of patients with pneumonia diagnosis at admission and those with prolonged MV. However, the choice of humidifiers should be made according to the clinical context, trying to avoid possible complications and reaching the appropriate performance at lower costs.

Keywords: Artificial airway occlusion; Heat and moisture exchangers; Heated humidifiers; Mortality; Pneumonia.

Fig. 1

The study selection process

Fig. 2

Artificial airway occlusion comparing the heat and moisture exchanger (HME) with the heated humidifier (HH). Weights: Kirkegaard 6.8%, Martin 7.1%, Misset 15.3%, Roustan 7.1%, Dreyfuss 5.9%, Branson 4.2%, Villafane 10.7%, Boots (2006) 4.2%, Hurni 5.9%, Kirton 6.6%, Kollef 4.1%, Lucchetti 6.9%, Lacherade 10.8%, boots (1997) 4.1%

Fig. 3

Upper box artificial airway occlusion comparing the heat and moisture exchanger (HME) and the heated humidifier (HH) with heated wire. Weights: Branson 11%, Boots (1997) 11%, Kirton 19.2%, Kollef 11%, Lacherade 36.8% Boots (2006) 10.9%. Lower box artificial airway occlusion comparing HME and HH with non-heated wire. Weights: Kirkegaard 8.9%, Martin 9.7%, Misset 30%, Roustan 9.8%, Dreyfuss 7.7%, Villafane 16.8%, Hurni 7.7%, Lucchetti 9.3%

Fig. 4

Incidence of pneumonia comparing the heat and moisture exchanger (HME) with the heated humidifier (HH). Weights: Martin 2.5%, Roustan 4.7%, Dreyfuss 5%, Branson 2.3%, Boots (1997) 5%, Kirton 8.6%, Kollef 9.1%, Memish 9.4%, Diaz 5.5%, Lacherade 19.5%, Lorente 8.4%, Boots (2006) 14.3%, Oguz 5.1%

Fig. 5

Upper panel: incidence of pneumonia comparing the heat and moisture exchanger (HME) and the heated humidifier (HH) with heated wire. Weights: Branson 5.7%, Boots (1997) 9.3%, Kirton 15%, Kollef 15.7%, Lachede 22%, Lorente 12.6%, Boots (2006) 19.7%. Lower panel incidence of pneumonia comparing HME and HH with non-heated wire. Weights: Martin 7.8%, Roustan 15.5%, Dreyfuss 16.7%, Memish 37.9%, Diaz 11.8%, Oguz 10.2%

Fig. 6

Upper panel mortality comparing the heat and moisture exchanger (HME) with the heated humidifier (HH). Weights: Kirkegaard1%, Martin 3.4%, Roustan 4.6%, Dreyfuss 5.4%, Boots (1997) 1.6%, Hurni 7.9%, Kollef 16.1%, Memish 14.5%, Diaz 2.6%, Lacherade 28.3%, Boots (2006) 14.4%. Middle panel mortality comparing HME and HH with heated wire. Weights: Boots (1997) 4%, Boots (2006) 28.9%, Kollef 27.9%, Lacherade 39.2%. Lower box mortality comparing HME and HH with non-heated wire. Weights: Diaz 6.2%, Dreyfuss 15.6%, Hurni 17.51%, Kirkegaard 3.1%, Martin 9.2%, Memish 34.9%, Roustan 13.5%

Fig. 7

Meta-regression on artificial airway occlusion including duration of mechanical ventilation (β = 2.637; p = 0.054) and pneumonia (β = 1.794; p = 0.012) as covariate. HME heat and moisture exchanger, HH heated humidifier