Safety, efficacy, and cost-effectiveness of mechanical ventilation with humidifying filters changed every 48 hours: A prospective, randomized study

Objective: To determine whether three hydrophobic and hygroscopic heat and moisture exchangers (HMEs) retain their heating and humidifying properties (assessed by psychrometric measurements of absolute humidity, relative humi dity, and tracheal temperature) for 48 hrs without any drop in their bacter iologic efficiency. Design: Prospective randomized clinical trial. Patients: Sixty-one consecutive unselected mechanically ventilated intensiv e care unit patients. Interventions: Patients were randomly allocated to one of the three HMEs st udied (Hygrobac-Dar from Mallinckrodt, n = 21; Humid-Vent from Gibeck, n = 20; and Clear-Thermal from Intersurgical, n = 20). Measurements and Main Results: Hygrometric parameters were measured by psyc hrometry after 3, 24, and 48 hrs of use. Peak airway pressure was recorded every 6 hrs and averaged over 24 hrs. Bacterial colonization of both patien ts and circuits was studied. Patients in all three groups were similar in t erms of age, indications for, and overall duration of mechanical ventilatio n. Tracheal tube occlusion never occurred. Hygrometric data included 371 me asurements whereas bacteriologic data included >700 samples and cultures. T he Hygrobac-Dar HMEs gave a significantly higher absolute humidity whatever the time of measurement (3, 24, or 48 hrs) than the other two HMEs (p < .0 01). The Clear-Thermal HMEs gave the poorest hygrometric parameters (p < .0 1); five of them were replaced prematurely (24 hrs) because the absolute hu midity was <25 mg H2O/L. This did not occur for the other HMEs. Mean peak a irway pressures were identical in the three groups, The bacterial colonizat ions of both patient and circuit were similar land negligible for circuits) for all three groups. Conclusion: Some HMEs may be used safely for 48 hrs without change. However , this does not pertain to every brand of HME. Objective in vivo evaluation of their humidifying performances is decisive before extending their durat ion of use.