The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

DO TIDAL VOLUMES AND FLOW RATES AFFECT RELATIVE HUMIDITY AND TEMPERATURE?

Kyle Jendral, David Vines, Keith R. Hirst; Dept. of Respiratory Care, Rush University, Chicago, IL

Background: Humidity is a vital part of the respiratory system and thus an important aspect of proper mechanical ventilation. When the upper airway is bypassed via ETT or tracheotomy then a humidity deficit may be created leading to complications with retained secretions. The purpose of this bench study is to determine if either tidal volume or 's (Irvine, CA) ability to deliver heated, humidified gas during mechanical ventilation. Methods: Each humidifier was placed in-line with a dual heated wire adult ventilator circuit. A thermo-hydrometer was placed in-line using a 22mm t-piece adapter immediately after the distal portion of the heated wire, just prior to the patient wye on the inspiratory side and after the inline suction device before the endotracheal tube (ETT). Relative humidity and temperature were recorded at both locations at various tidal volumes and flow rates. Results: It was seen that as tidal volume and flow rates increase there was a significant increase in temperature at the start of the ETT. Tidal volumes of 400 were found to have the highest mean relative humidity (98.41%) at the start of the ETT compared to 95.84% for tidal volumes of 600, 96.81% for tidal volumes of 800, and 96.51% for tidal volumes of 1230, respectively. The relative humidity prior to the start of the ETT was greatest at the flow rate of 40lpm (97.56%) compared to flows of 60lpm (95.59%) and 80lpm (96.59%). When relative humidity and temperature were converted to absolute humidity there were no significant clinical differences with changes in tidal volume and flow (Table 1). Conclusion: Neither humidifier tested outperformed the other. Although relative humidity, temperature, and thus absolute humidity varied with tidal volume and flow, both humidifiers were able to meet the minimum humidification (30 mgH20/L) and temperature (30 degrees C) recommendations of the AARC clinical practice guidelines for humidification during mechanical ventilation.
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Mean Absolute Humidity (mgH20/L)