Objective: Many heat and moisture exchangers with filter (HMEF) have been developed. In-house data from companies provide some information about their performances; unfortunately, to our knowledge, no comparative evaluation in clinical conditions has been undertaken of these newer products. The aim of this study was to compare the efficiency of two HMEFs, one hydrophobic and one hygroscopic, on humidifying capacity and the rate of bronchial colonization and ventilator-associated pneumonia in ICU patients.
Design: Prospective, randomized study.
Setting: ICU of a university hospital.
Patients: All patients who required mechanical ventilation for [is greater than or equal to] 24 h during the study period.
Interventions: On admission to the ICU, patients were randomly assigned to one of two groups. In one group, the patients were ventilated with a hygroscopic device (Humid-Vent Filter Light HMEF; Gibeck; Upplands Vaesby, Sweden). The condensation surface was made of paper (Microwell) impregnated with Ca[Cl.sub.2]. The filter membrane was made of polypropylene. In the other group, the patients were ventilated with a hydrophobic device (Pall BB100 HMEF). The condensation surface was made of a hydrophobic resin with a hydrophylic layer. The filter membrane was made of ceramic fibers. In both groups, HMEFs were changed daily.
Measurements and results: Both groups of patients were similar for the tested characteristics, including parameters of mechanical ventilation. Sixty-six patients were ventilated for 11.7 [+ or -] 11 days with the Humid-Vent Filter Light HMEF and 70 patients for 12.2 [+ or -] 12 days with the Pall BB 100. Patients ventilated with the Humid-Vent Filter Light underwent 6.0 [+ or -] 3.0 tracheal aspirations and 1.7 [+ or -] 2.0 instillations per day, and those with the Pall BB 100, 6.0 [+ or -] 3.0 and 1.6 [+ or -] 2.0 per day, respectively (not significant [NS]). Abundance of tracheal secretions, presence of blood, and viscosity, evaluated by semiquantitative scales, were similar in both groups. No difference in the rate of atelectasis was observed between the two groups (7.5% and 7.1%, NS). One episode of tracheal tube occlusion was observed with the Humid-Vent Filter Light HMEF, and one with the other HMEF (NS). One patient in each group (NS) was switched to an active heated humidifier because of very tenacious bronchial secretions despite repeated instillations. Tracheal colonization was observed at a rate of 67% with the Humid-Vent Filter Light and 58% with the Pall BB 100 (NS). A small, but NS difference was observed in the rate of ventilator-associated pneumonia: Humid-Vent Filter Light, 32% (27.1 per 1000 ventilator days); and Pall BB 100, 37% (30.4 per 1000 ventilator days). Bacteria responsible for tracheal colonization and pneumonia were similar in both groups. Three patients in each group died from their nosocomial pneumonia. Conclusion: Despite differences in their components, the two HMEFs tested achieved similar performances in terms of humidification and heating of inspired gases. Only one episode of endotracheal tube occlusion was detected and very few patients (one in each group) had to be switched to an active heated humidifier. No difference was observed either in the rate of tracheal colonization or of ventilator-associated pneumonia. These data show that the hygroscopic HME (Humid-Vent Filter Light) and the hydrophobic HME (Pall BB 100) are suited for use in ICU patients.
Key words: bronchial colonization; heat and moisture exchanger; mechanical ventilation; nosocomial pneumonia; ventilatory gases
Abbreviations: HME = heat and moisture exchanger; HMEF = heat and moisture exchanger filter; NS = not significant
Mechanical ventilation with dry, cold gases leads to impaired function of the mucociliary elevator, subsequent sputum retention and atelectasis, reduced functional residual capacity, hypoxia, increased incidence of pneumonia, and heat loss.[1-8]
Heat and moisture exchangers (HMEs) with microbial filtration capacity (HME filters, HMEFs) might be a simple solution to the problems of conditioning respiratory gases and, eventually, of reducing the contamination of apparatus and subsequent bacterial pneumonia.[9-15]
An important advance in the design of HMEs was made with the introduction of plastic foam or paper condensation surfaces impregnated with a hygroscopic substance as the active element.[12-16] Different hygroscopic compounds are used to improve water retention capacity: Ca[Cl.sub.2], Al[Cl.sub.3], Mg[Cl.sub.2], and LiCl.
HMEFs combine the humidification properties with the bacterial retention properties of a filter membrane.[16-18] Efficient microbial filtration may be especially important in the infected or immunocompromised patient in the ICU and HMEFs may help protect both patients and ventilators from microbial cross-contamination.[16-18]
The humidifying efficiency of hydrophobic HMEFs is a matter of controversy. The performance is notably dependent on the tidal volume given to the patients[13-15,19] and some studies report endotracheal tube occlusion because of inadequate airway humidification with the use of HMEFs in patients in the ICU.[20-22]