Impact of passive humidification on clinical outcomes of mechanically ventilated patients: A meta-analysis of randomized controlled trials

Objective: Previous meta-analyses reported advantages of passive (i.e., heat and moisture exchangers, or HMEs) compared with active (i.e., heated humidifiers, or HHs) humidifiers in reducing the incidence of ventilator-associated pneumonia, but they did not examine the effect of these devices on mortality, length of intensive care unit stay, and duration of mechanical ventilation. In addition, relevant data-were recently published. Design: Meta-analysis of randomized controlled trials comparing HMEs with HHs for the management of mechanically ventilated patients to determine the impact of these devices on clinical outcomes of such patients. Methods: We searched PubMed and the Cochrane Central Register of Controlled Trials as well as reference lists from publications, with no language restrictions. We estimated pooled odds ratios (ORs) and 95% confidence intervals (CIs), using a random effects model. Results: Thirteen randomized controlled trials, studying 2,580 patients, were included. There was no difference in incidence of ventilator-associated pneumonia among patients managed with HMEs and HHs (OR 0.85, 95% CI 0.62-1.16). There was no difference between the compared groups regarding mortality (OR 0.98, 95% CI 0.80-1.20), length of intensive care unit stay (weighted mean differences, -0.68 days, 95% CI -3.65 to 2.30), duration of mechanical ventilation (weighted mean differences, 0.11 days, 95% CI -0.90 to 1.12), or episodes of airway occlusion (OR 2.26, 95% CI 0.55-9.28). HMEs were cheaper than HHs in each of the randomized controlled trials. Conclusion: The available evidence does not support the preferential performance of either passive or active humidifiers in mechanical ventilation patients in terms of ventilator-associated pneumonia incidence, mortality, or morbidity.