OC Kirton, B DeHaven, J Morgan, O Morejon, J Civetta. A prospective, randomized comparison of an in-line heat moisture exchange filter and heated wire humidifiers: rates of ventilator-associated early-onset (community-acquired) or late-onset (hospital-acquired) pneumonia and incidence of endotracheal tube occlusion. Chest 1997; 112:1055-1059.

The use of heat and moisture exchanging filters in place of hot water humidification has been investigated by a number of authors. In this paper, a large prospective randomized clinical study, conducted in a 20-bed intensive care unit, demonstrated that the incidence of VAP could be significantly reduced by the use of a Pall pleated hydrophobic membrane breathing system filter.

280 patients were randomized to humidification with either the Pall BB100 Breathing System Filter or a heated wire humidifier. Filters were changed daily, or more often if required, and ventilator circuits were changed weekly. Patients were removed from the filter group if the filter required changing more than three times during a 24-hour period, or if ultra-high frequency ventilation was clinically indicated. Pneumonia was diagnosed according to CDC criteria: pneumonia developing within the first three days of ventilation was defined as community-acquired pneumonia, development after three days was defined as hospital-acquired ventilator-associated pneumonia. A sub-group of 52 patients in the filter group were monitored for total work of breathing, elastic work of breathing and resistive work of breathing. Endotracheal tube occlusion was assessed at extubation and during flexible bronchoscopy. Duration of ventilation and ICU stay was measured and ventilator circuit costs were recorded for each group.

The filter group had a significantly lower VAP rate (6% versus with 16%), significant lower ventilator circuit costs and shorter stay in ICU. There were no differences in either partial endotracheal tube occlusion (a clinical measure of humidification) or Work of Breathing.

The authors conclude that:

"A significant reduction in the incidence of late-onset, hospital acquired VAP...was realized with the Pall BB100 HMEF, associated with a significant reduction in the number of TICU days consumed by the patients. Projected savings exceed two ICU beds for the year.....Total capacity of the TICU was increased by 10%...with no increase in cost or resource outlays. Disposable ventilator circuit costs were significantly less in the HMEF group."

The same group has also recently presented an update to the main study, showing that the antibiotic costs were also dramatically reduced by the use of the Pall BB100 Breathing System Filter. This is not unexpected, considering the reduction in VAP in the filter group. The total cost of antibiotics in the filter group was $4700, compared with $22,600 in the heated wire group.