The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

Evaluation of Condensation in Three Commercially Available Heated Wire Ventilator Circuits

Kathleen Deakins RRT-NPS, Juliann Di Fiore BSEE Rainbow Babies & Children's Hospital, Cleveland Ohio

Introduction: Dualheated wire ventilator circuits, a standard of care for neonatal mechanical ventilation, are used to deliver optimal temperature and humidification of inspired gas. These designs may result in excess condensation and contamination of the ventilator circuit. This study was designed to evaluate the level of condensation in 3 commercially available heated wire infant ventilator circuits under controlled environmental conditions.

Methods: Three circuits were compared

1. Airlife Isothermal Infant Respiratory Circuit RT4851, conventional straight heated wire design; MR 850 humidifier (Fisher & Paykel).

2. Fisher & Paykel Neonatal Ventilation Circuit RT235, coiled heated wire in inspiratory limb; Nafion tubing and straight heated wire in expiratory limb; MR850 humidifier (Fisher & Paykel).

3. Hudson RCI Heated Wire Neonatal Ventilator Circuit 780-07; semi-coiled heated wire inspiratory and expiratory limbs; Conchatherm IV Plus humidifier (Hudson RCI).

Experiments were conducted in a non patient care area (room temp. 23°C) over a 72 hour period. Circuits were attached to test lungs placed in a heated and humidified incubator (Ohmeda Care Plus, Ohmeda Medical) set at 37°C and ventilated with Infant Star ventilators (frequency 20/min, PIP/PEEP 20/5 cm H20, flow 10 L/min, Fi02 0.21). Typical humidifier settings used in clinical practice were employed: MR 850:intubated mode and Conchatherm IV Plus at the "dry" setting (+3°C temperature gradient). Levels of condensation were measured volumetrically throughout 24, 48 and 72 hour periods. The experiment was repeated three times for each set of circuits under the same conditions.

Results: Minimal condensation was seen in the Fisher & Paykel circuit. The Airlife and Hudson circuits had much higher levels of condensation. There was a large variability in the amount of condensation with repeated measurements as shown by a large standard deviation with the Airlife and Hudson circuits (Table):

Levels of Measured Condensation (mL, mean ± SD)
  Fisher & Paykel Airlife Hudson
Time Inspiratory Expiratory Inspiratory Expiratory Inspiratory Expiratory
24h 0.00±0.00 0.00±0.00 0.47±0.81 5.43±2.68 1.70±0.85 3.10±1.35
48h 0.03±0.06 0.00±0.00 5.90±3.41 6.03±2.83 6.17±3.09 4.30±1.40
72h 0.17±0.15 0.00±0.00 2.03±0.55 3.40±2.48 3.33±1.26 3.30±3.73
Total 0.20±0.17 0.00±0.00 7.8±4.14 14.87±6.67 11.20±4.35 10.70±6.48
Total 0.20 ± 0.17 22.67 ± 8.20 21.90 ± 5.81

Conclusion: The Fisher & Paykel heated ventilator circuit had 99% less condensation than the Hudson and Airlife circuits. This may be due to differences in heater coil design (coiled versus straight wire) and/or the additional insulation and evaporation (Nafion) properties utilized in the Fisher & Paykel circuit. We assume the circuits delivered relative humidity near 100% because all had condensation in the inspiratory limb, but future studies should confirm this.

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