(1151) Effect of Turning off Humidification on Aerosol Delivery and Humidity During Mechanical Ventilation

Introduction: During mechanical ventilation, inspired gases require heat and humidification. However, such conditions are associated with reduced aerosol delivery efficiency. The practice of turning off heated humidification prior to nebulization and the impact of nebulization on humidity in a dry ventilator circuit remain topics of debate. This study aimed to assess the effect of turning off heated humidification on inhaled dose and humidity with nebulizer use during adult mechanical ventilation.

Methods: A bronchodilator (albuterol) and two antibiotics (Colistimethate sodium and Amikacin sulfate) were nebulized with a vibrating-mesh and a jet nebulizer placed at the inlet of the humidifier and in the inspiratory limb at the Y-piece. Aerosol particle size distribution was determined via a cascade impactor. Absolute humidity and temperature of inspired gases were determined with anemometer/hygrometers before, during and after nebulization, prior to, during and up to 60 min after interrupting active humidification. Aerosol collected on a filter distal to the endotracheal tube and on impactor stages were eluted and assayed by spectrophotometry.

Results: Inhaled dose was increased with a vibrating mesh nebulizer after humidifier turned on and decreased after turning off the humidifier. With a jet nebulizer, inhaled dose was decreased after humidifier was on and further decreased after humidifier was turned off. The aerosol particle size ranged from 1.1 to 2.7 μm. With interruption of active humidification, humidity of inspired gas quickly dropped below recommended levels, and nebulization in dry ventilator circuit produced an absolute humidity between 10–20 mgH2O/L, lower than the recommended minimum of 30 mgH2O/L.

Conclusions: Interrupting active humidification during mechanical ventilation prior to nebulization did not improve aerosol delivery efficiency for bronchodilator or antibiotics, but did reduce humidity below recommended levels.