The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

DECREASED AMBIENT TEMPERATURE AND FAN BREEZE DECREASES DELIVERED ABSOLUTE HUMIDITY FROM A VENTILATOR CIRCUIT

Tim Op’t Holt, Charles Langley; Cardiorespiratory Care, Univ of South Alabama, Mobile, AL

Background: Maintaining adequate humidity to patients receiving mechanical ventilation is an important aspect of maintaining physiologic humidity and tracheobronchial hygiene. Ambient temperature of the ventilated patient’s room and the presence of a box fan in the room are not often considered when delivering heated humidity. We sought to determine the effect of ambient temperature and the presence of a box fan blowing in the vicinity of the ventilator circuit on absolute humidity and humidity deficit. Method: The ambient temperature in an intensive care unit was determined. In an in vitro bench study, we measured the temperature and relative humidity of gas being delivered to a test lung ventilated with a Servo 900C ventilator with a hygrometer. Humidity was provided by a Fisher & Paykel MR850 via a Fisher & Paykel RT100 dual heated wire circuit. The Hygro-thermometer sensor was placed between the Y-piece and the test lung. Absolute humidity was calculated from the relative humidity and temperature. This study was done with an ambient room temperature of 23-24 degrees C and 20-21 degrees C. The ventilator circuit and patient interface were subjected to breeze from a fan at three speeds and both temperatures. A balanced ANOVA was used to analyze the data. Results: In the cooler room, the mean delivered absolute humidity level was less than the mean delivered absolute humidity in the warmer room (p<.000). When the fan speed was set to low or high, the mean absolute humidity level decreased further (p<.000). Humidity deficit increased with a decrease in room temperature or an increase in fan speed (p<.000). Conclusions: Delivered absolute humidity and humidity deficit were affected by the ambient room temperature as well as breeze from a fan. The compounding effect of both ambient temperature and breeze cooling the circuit was significant. Delivered absolute humidity decreases below recommended levels in the presence of breeze from a fan, which may have clinical consequences. Sponsored Research - None

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