CLINICAL UTILITY OF HYGROSCOPIC HEAT AND MOISTURE EXCHANGERS IN INTENSIVE-CARE PATIENTS

Objective: To compare the degree of bacterial circuit colonization, fr equency of ventilator-associated pneumonia (VAP), character of respira tory secretions, rewarming of hypothermic patients, disposable costs, and air flow resistance in intensive care patients ventilated using ei ther a heat and moisture exchanger (HME) or hot water (HW) humidifier circuit. Design: A prospective, randomized blinded trial of patients i n the intensive care unit undergoing mechanical ventilation. Setting: A metropolitan teaching hospital. Patients: One hundred sixteen patien ts undergoing mechanical ventilation for a minimum period of 48 hrs we re enrolled. Interventions: Patients were randomized to three ventilat ion 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 an d Main Results: Circuit colonization was assessed using quantitative c ulture of washings taken from the circuit tubing and semiquantitative culture of swabs from the Y connectors. Sixty seven percent of HW circ uits 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 frequenc y of VAP, the time to resolution of admission hypothermia, and the vol ume and fluidity of secretions were similar for all groups. The resist ance of the HME after 24 hrs of use was <0.025 cm H2O/L at gas flows o f 40 L/min. HME use resulted in a cost reduction of $1.48 (Australian) /day. Conclusions: Circuits with a bacterial viral filtering HME are l ess readily colonized by bacteria. Contamination is a random event. Hu midification technique has no influence on the frequency rate of VAP, the effectiveness of rewarming, nor the character of the respiratory s ecretions. Breathing resistance is generally low and disposable costs are reduced when an HME is used.