Clinical utility of hygroscopic heat and moisture exchangers in intensive care patients

OBJECTIVE: To compare the degree of bacterial circuit colonization, frequency of ventilator-associated pneumonia (VAP), character of respiratory secretions, rewarming of hypothermic patients, disposable costs, and air flow resistance in intensive care patients ventilated using either a heat and moisture exchanger (HME) or hot water (HW) humidifier circuit. DESIGN: A prospective, randomized blinded trial of patients in the intensive care unit undergoing mechanical ventilation. SETTING: A metropolitan teaching hospital. PATIENTS: One hundred sixteen patients undergoing mechanical ventilation for a minimum period of 48 hrs were enrolled. INTERVENTIONS: Patients were randomized to three ventilation groups using a) an HW circuit with a 2-day circuit change (n = 41) ; or b) a bacterial-viral filtering HME in the circuit, with either a 2-day (n = 42) ; or c) a 4-day circuit change (n = 33). MEASUREMENTS AND MAIN RESULTS: Circuit colonization was assessed using quantitative culture of washings taken from the circuit tubing and semiquantitative culture of swabs from the Y connectors. Sixty-seven percent of HW circuits became contaminated compared with 12% in the two HME groups (p <. 0001). Median colony counts were lower in the HME groups (p <. 0001). If circuits at first circuit change were contaminated in the HW group, 89% of subsequent circuit changes became contaminated compared with 0% and 25% for the 2- and 4-day HME groups, respectively. The frequency of VAP, the time to resolution of admission hypothermia, and the volume and fluidity of secretions were similar for all groups. The resistance of the HME after 24 hrs of use was < 0. 025 cm H2O/L at gas flows of 40 L/min. HME use resulted in a cost reduction of 1. 48 (Australian) /day. CONCLUSIONS: Circuits with a bacterial-viral filtering HME are less readily colonized by bacteria. Contamination is a random event. Humidification technique has no influence on the frequency rate of VAP, the effectiveness of rewarming, nor the character of the respiratory secretions. Breathing resistance is generally low and disposable costs are reduced when an HME is used.