Passive Humidification on Clinical Outcomes of MV Patients
Passive Humidification on Clinical Outcomes of MV Patients
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.
Warming and humidifying the gases delivered to patients under invasive mechanical ventilation (MV) is common practice because it prevents injury of the respiratory tract mucosa and prevents ventilator-associated pneumonia (VAP). VAP, a common infection in the intensive care unit (ICU), is associated with increased mortality, length of ICU stay, and healthcare costs.
Humidification of the inspired gases for the management of patients undergoing MV can be passive, performed by heat and moisture exchangers (HMEs) to allow condensation from the patient's expired air to be evaporated during inspiration, or it can be active, performed by heated humidifiers (HHs), in which the inspired gases pass across or over a heated water bath. An HME may be hygrophobic or hygroscopic (i.e., containing hygroscopic salts to improve moisture retention). An HME may also contain a filter (i.e., a heat and moisture-exchanging filter). On the other hand, an HH may contain heated wire circuits to avoid formation of ventilator tubing condensate, which has been blamed for enhancing the risk for VAP development. It has been advocated that each of these humidification systems may have advantages in preventing VAP: HMEs by reducing contaminated condensate in the ventilator circuit, and HHs by preserving mucociliary clearance, because they can condition inspired gas to a higher absolute humidity level than HMEs.
Although the passive operation and feasibility of HMEs have popularized their use in recent years, controversy exists about their advantage over HHs for the prevention of VAP. Indeed, in three systematic reviews, the authors stated that HMEs were associated with VAP rates that were either similar to or lower than VAP rates associated with HHs; however, these authors emphasized that the relevant evidence was inconclusive.
In 2003, Hess et al. performed a meta-analysis of six randomized controlled trials (RCTs) that compared HMEs with HHs for the management of patients undergoing MV; the combined effect from this analysis demonstrated a lower VAP incidence for the use of passive than active humidifiers. Even more recently (2005), Kola et al. conducted a meta-analysis of this aspect by including eight relevant RCTs; these authors found a reduction in the incidence of VAP in patients managed with HMEs, particularly in patients ventilated for ≥7 days. However, the results of these two meta-analyses may have been affected by the large difference in outcomes in one of the included RCTs, a limitation clearly noted by Hess et al.. Also, these two meta-analyses did not examine the effect of the different methods of humidification on other, also important, outcomes, such as mortality, duration of mechanical ventilation, and ICU length of stay. One may agree that it is difficult to reconcile reduction in VAP risk due to an intervention with an absence of effect of the same intervention on the previously mentioned outcomes.
In the last few years, three additional large RCTs on this issue have been published. Reporting conflicting results, these trials enhanced the debate about the preferential use of passive or active humidifiers. Thus, we endeavored to exploit the growing body of evidence to evaluate the comparative impact of passive (HMEs) and active (HHs) humidification on outcomes of patients undergoing MV, by performing a meta-analysis of relevant RCTs.
Abstract and Introduction
Abstract
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.
Introduction
Warming and humidifying the gases delivered to patients under invasive mechanical ventilation (MV) is common practice because it prevents injury of the respiratory tract mucosa and prevents ventilator-associated pneumonia (VAP). VAP, a common infection in the intensive care unit (ICU), is associated with increased mortality, length of ICU stay, and healthcare costs.
Humidification of the inspired gases for the management of patients undergoing MV can be passive, performed by heat and moisture exchangers (HMEs) to allow condensation from the patient's expired air to be evaporated during inspiration, or it can be active, performed by heated humidifiers (HHs), in which the inspired gases pass across or over a heated water bath. An HME may be hygrophobic or hygroscopic (i.e., containing hygroscopic salts to improve moisture retention). An HME may also contain a filter (i.e., a heat and moisture-exchanging filter). On the other hand, an HH may contain heated wire circuits to avoid formation of ventilator tubing condensate, which has been blamed for enhancing the risk for VAP development. It has been advocated that each of these humidification systems may have advantages in preventing VAP: HMEs by reducing contaminated condensate in the ventilator circuit, and HHs by preserving mucociliary clearance, because they can condition inspired gas to a higher absolute humidity level than HMEs.
Although the passive operation and feasibility of HMEs have popularized their use in recent years, controversy exists about their advantage over HHs for the prevention of VAP. Indeed, in three systematic reviews, the authors stated that HMEs were associated with VAP rates that were either similar to or lower than VAP rates associated with HHs; however, these authors emphasized that the relevant evidence was inconclusive.
In 2003, Hess et al. performed a meta-analysis of six randomized controlled trials (RCTs) that compared HMEs with HHs for the management of patients undergoing MV; the combined effect from this analysis demonstrated a lower VAP incidence for the use of passive than active humidifiers. Even more recently (2005), Kola et al. conducted a meta-analysis of this aspect by including eight relevant RCTs; these authors found a reduction in the incidence of VAP in patients managed with HMEs, particularly in patients ventilated for ≥7 days. However, the results of these two meta-analyses may have been affected by the large difference in outcomes in one of the included RCTs, a limitation clearly noted by Hess et al.. Also, these two meta-analyses did not examine the effect of the different methods of humidification on other, also important, outcomes, such as mortality, duration of mechanical ventilation, and ICU length of stay. One may agree that it is difficult to reconcile reduction in VAP risk due to an intervention with an absence of effect of the same intervention on the previously mentioned outcomes.
In the last few years, three additional large RCTs on this issue have been published. Reporting conflicting results, these trials enhanced the debate about the preferential use of passive or active humidifiers. Thus, we endeavored to exploit the growing body of evidence to evaluate the comparative impact of passive (HMEs) and active (HHs) humidification on outcomes of patients undergoing MV, by performing a meta-analysis of relevant RCTs.
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