Key Point

Either heated humidifiers or heat and moisture exchangers can be used without increasing the risk of ventilator-associated pneumonia in ICU patients receiving mechanical ventilation.

PARIS—Heated humidifiers and heat and moisture exchange systems are the two types of humidification systems currently used in ICU patients who are receiving mechanical ventilation. Which of these systems carries a greater risk of ventilator-associated pneumonia (VAP), however, is a point of contention. To address this, French researchers used a randomized multicenter design to compare the risk and incidence of VAP while using heated humidifiers or heat and moisture exchangers: They found no difference between the two.¹

The study was conducted between February 2000 and June 2002 in five ICUs at two teaching hospitals. All patients were expected to require mechanical ventilation for more than 48 hours and were randomly assigned to humidification with either a heated humidifier or a heat and moisture exchanger. Both humidification systems were used in accordance with manufacturers’ instructions.

Patients were screened daily for VAP. However, pneumonia that occurred within 48 hours of ventilation was not considered VAP. Clinical suspicion of VAP was based on a recent and persistent infiltrate on a chest film and two of the following: fever or hypothermia, leukocytosis or leukopenia, and purulent tracheal secretions.

The primary end point was rate of VAP in each of the groups. Secondary end points included duration of mechanical ventilation, duration of ICU stay, ICU mortality rate, tracheostomy rate, and occurrence of endotracheal tube occlusion.

The study population was 369 (185 in the heat and moisture exchanger group and 184 in the heated humidifier group). Groups were similar for the most part. Two exceptions were that patients in the heated humidifier group had a higher Simplified Acute Physiology Score II, while the heat and moisture exchanger group had respiratory failure given more frequently as the primary diagnosis.

A clinical suspicion of pneumonia occurred in 40% of patients in the heat and moisture exchanger group and in 42% of the heated humidifier group. A total of 100 episodes of VAP occurred during the study period—47 in the heat and moisture exchanger group and 53 in the heated humidifier group. The between-group difference in VAP incidence was not significant, nor was there any significant difference in secondary end points. A total of 108 pathogens were isolated from the patients with VAP, and once again, there was no significant difference between groups.

The authors noted that although higher colonization rates of the ventilator circuits were previously reported with the use of heated humidifiers, "the lack of reduction in VAP rate with the use of [heat and moisture exchangers] found in our study suggests that circuit colonization plays little or no role in the occurrence of VAP." However, they continued, "new generations of [heated humidifiers] such as those used in our trial include heated ventilator circuits, which markedly reduce the formation of condensate; and with no water trap on the ventilator circuit, the risk of massive inoculation is reduced." They pointed out that their results may not be applicable to ICUs not using the same type of device.

The researchers concluded that either of the humidification systems can be used without having a significant impact on the incidence of VAP.

—Gale Jurasek

Reference
1. Lacherade J-C, Auburtin M, Cerf C, et al. Impact of humidification systems on ventilator-associated pneumonia: a randomized multicenter trial. Am J Respir Crit Care Med. 2005;172:1276-1282.

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