Molecular High Humidity in the Weaning of Patients from Mechanical Ventilation: A Case Report

Abstract

Inability to wean some patients from mechanical ventilation has been attributed to psychological dependence, to reduction in vital capacity, to inadequate inspiratory force, and to misuse of intermittent mandatory ventilation. We believe that airways reactivity to particulate water (aerosol) may also be a cause of failure to wean. Particulate water (aerosol generated by a nebulizer) is frequently used in administra- tion of oxygen mixtures to patients during initial trials off the ventilator. We observed one patient who developed acute distress when first placed on the nebulizer system as the final step in weaning him from the ventilator. The patient was then placed on a system that used a humidifier instead of a nebulizer and that delivered controlled concentrations of oxygen and molecular water at 90 to 95° F and 95 to 100% relative humidity. The patient's respiratory distress subsided dramatically while he was receiving molecular high humidity (MHH). Twenty-four hours later, when the patient was again placed on a nebulizer system and received aerosol (particulate water), he developed acute respiratory embarrassment within several minutes. One explanation for this phenomenon may be vagally mediated reflex bronchoconstric- tion, which increases airways resistance, thereby increasing the work of breathing. We conclude from our clinical observations in this patient and others that there is a reasonable basis for a trial of molecular high humidity in the weaning of some patients from mechanical ventilation.