Prolonged use of heat and moisture exchangers does not affect device efficiency or frequency rate of nosocomial pneumonia

Objective: To determine whether use of a single heat and moisture exchanger (HME) for less than or equal to 120 hrs affects efficiency, resistance, level of bacterial colonization, frequency rate of nosocomial pneumonia, and cost compared with changing the HME every 24 hrs. Design: Prospective, controlled, randomized, unblinded study. Setting: Surgical intensive care unit at a university teaching hospital. Patients: A total of 220 consecutive patients requiring mechanical ventilation for >48 hrs. Interventions: Patients were randomized to one of three groups: a) hygroscopic HME (Aqua+) changed every 24 hrs (HHME-24); b) hydrophobic HME (Duration HME) changed every 120 hrs (HME-120); and c) hygroscopic HME (Aqua+) changed every 120 hrs (HHME-120). Devices in all groups could be changed at the discretion of the staff when signs of occlusion or increased resistance were identified. Measurements and Main Results: Daily measurements of inspired gas temperature, inspired relative humidity, and device resistance were made. Additionally, daily cultures of the patient side of the device were accomplished. The frequency rate of nosocomial pneumonia was made by using clinical criteria. Ventilatory support variables, airway care, device costs, and clinical indicators of humidification efficiency (sputum volume, sputum efficiency) were also recorded. Prolonged use of both hygroscopic and hydrophobic devices did not diminish efficiency or increase resistance; There was no difference in the number of colony-forming units from device cultures over the 5-day period and no difference between colony-forming units in devices changed every 24 hrs compared with devices changed after 120 hrs. The average duration of use was 23 +/- 4 hrs in the HHME-24 group, 73 +/- 13 hrs in the HME-120 group, and 74 +/- 9 hrs in the HHME-120 group. Mean absolute humidity was greater for the hygroscopic devices (30.4 +/- 1.1 mg of H2O/L) compared with the hydrophobic devices (27.8 +/- 1.3 mg of H2O/L). The frequency rate of nosocomial pneumonia was 8% (8:100) in the HHME-24 group, 8.3% (5:60) in the HME-120 group, and 6.6% (4:60) in the HHME-120 group. Pneumonia rates per 1000 ventilatory support days were 20:1000 in the HHME-24 group, 20.8:1000 in the HME-120 group, and 16.6:1000 in the HHME-120 group. Costs per day were $3.24 for the HHME-24 group, $2.98 for the HME-120 group, and $1.65 for the HHME-120 group. Conclusions: Changing the hydrophobic or hygroscopic HME after 3 days does not diminish efficiency, increase resistance, or alter bacterial colonization. The frequency rate of nosocomial pneumonia was also unchanged. Use of HMEs for >24 hrs, up to 72 hrs, is safe and cost effective.