The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

THE EFFECT OF OPTIMAL HUMIDITY ON VENTILATOR-ASSOCIATED PNEUMONIA RATES

Fran Piedalue, RRT University of Colorado Hospital, Denver, Colorado

Introduction: Controversy exists as to the appropriate temperature and humidity of inspired gas delivered to mechanically ventilated patients with artificial airways. Current AARC Clinical Practice Guidelines recommends 33± 2 ° C with a minimum of 30 mg/L of water vapor. A recent publication, Williams et al1, provides evidence that inspired humidity must reach optimal level or mucosal dysfunction will occur. This optimal level is 37 ° C with 100% relative humidity and 44 mg/L. Optimal humidity offers a significant therapeutic benefit to the patient of improved mucociliary clearance. Because maximum mucociliary transport defends the lung against infection, the use of optimal humidity may result in a decrease rate of Ventilator Associated Pneumonia.

Methods:
Humidification systems for all mechanically ventilated patients with artificial airways were set as follows: humidification chamber set at 37 ° C with 100% relative humidity, heating wires in the inspiratory line of the ventilator circuit set to maintain a temperature of 39-40 ° C at the inspiratory side of the circuit wye. Temperature drop from circuit wye to patient airway was estimated to be 2-3 °. Delivery of inspired gas to patient airway inside of patient estimated to be 37 ° C and 100% relative humidity.

Results:
The University of Colorado Hospital has monitored VAP for the past 4 consecutive years. For the first 3 years, the VAP yearly rate averaged consistently 15-16%. The 4th year, after the change to optimal humidity, the yearly rate was 8%. The surgical population was the group with the largest decrease. Conclusion: The use of optimal humidity coincided with a 50% reduction in VAP rate at the University of Colorado Hospital. Further investigation of optimal humidification on patient outcome is underway. 1. Williams R et al: Relationship between the humidity and temperature of inspired gas and the function of the airway mucosa. Crit Care Med 1996;24(11):1920-1929. (See Original for Figure)

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