The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

THREE HUMIDIFICATION TECHNIQUES DURING PEDIATRIC VENTILATION.

John Salyer BS, RRT, AI Bailey RRT, Madolin Witte MD. Primary Children's Medical Center, University of Utah School of Medicine, Salt Lake City, UT.

Introduction: We sought to determine the inspired and expired absolute humidity (AH_{I} & AH_{E}) during the use of a heat and moisture exchanger (HME) and a wick humidifier at two different temperatures during pediatric mechanical ventilation. Methods: A measurement chamber was constructed that isolated inspiratory from expiratory flow and fit between the ETT tip and the ventilator circuit. AH_{I} and AH_{E} were measured using a polymer film capacitive sensor with a built-in heating coil that controlled sensor temperature to 47 degrees C to avoid condensation. Eligible subjects included any stable patients ventilated in our PICU who did not have asthma, BPD, cavitating lung disease, or CF. After informed consent, each patient was studied for two hours under all three of the following conditions in random order: (1) use of an HME (Gibeck Humid-Vent), (2) use of a wick-type humidifier set at 34 degrees (Fisher-Paykel), or (3) use of a wick-type humidifier set at 39 degrees. The HME's were sized according to patient tidal volume and placed distal to the measuring chamber. Humidity measurements were taken at the start of each arm and every 30 minutes and were averaged for each patient. Differences were tested for statistical significance (P < 0.05) using ANOVA. Results. Thirteen patients have been studied so far (median age = 5.7 yrs) We discovered statistically significant differences in AH_{I} between all three arms and in AH_{E} between the HME and T-34 arm. There were also statistically significant differences between AH_{I} and AH_{E} within each arm except the 39 degree arm. Discussion: The HME's are far below the output of the heated humidifiers and do not meet published recommendations of >28 mg/L (Branson et al. Respir Care 1996;41:736-743), and thus are probably unsuitable for use in pediatric patients. ASTM 1690 and ISO 8185 standards for heated humidifiers say that all such devices should be capable of producing AH_{I} of 33 mg/L. Operated at 34 degrees, these wick-type humidifiers do not meet that standard. Whether the differences in humidification affect patient outcomes has not been determined.

(See original for figure)

OF-97-135

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