The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

Comparing Resistance Across The Expiratory LIMB of the Limb-O Circuit vs a Heated-Wire Circuit

Ross Armstrong RRT1, Nikolas Sirs RRT2, Lonny Ashworth MEd RRT3. 1St. Luke's Regional Medical Center, Boise, ID 2Northern Colorado Medical Center, Greeley, CO 3Boise State University, Boise, ID

Background: The Limb-O circuit (Vital Signs, Inc.) is a single-lumen circuit designed to have less tubing at the bedside, no need for additional humidification and less weight on the patient's airway. Equipped with a heat moisture exchanger (HME), the Limb-O circuit is commonly used on patients who require shorter periods of mechanical ventilation or during noninvasive mechanical ventilation. According to the manufacturer, the smooth common wall found inside the tubing, reduces turbulent flow resulting in a resistance that is comparable to a traditional ventilator circuit. The purpose of this study is to evaluate the resistance across the expiratory limb of the circuit when using a Limb-O circuit versus a traditional heated-wire circuit.

Methods: A Dräger XL ventilator, with a CMV rate 12 BPM and tidal volume 500 mL, was used with a Limb-O circuit and heated-wire circuit. To measure the resistance across the circuit, pressure and flow transducers were connected at the patient wye and immediately before the exhalation valve. Each circuit was then connected to a Hans Rudolph Electronic Breathing Simulator (HR 1101). A compliance of 100, 80, 60, 40 and 20 mL/cm H2O and PEEP of 3, 6, 9, 12 and 15 cm H2O were used.

Results: The expiratory resistance was higher using the Limb-O circuit than the heated-wire circuit at each compliance and PEEP setting. At PEEP of 6 cm H2O and decreasing compliance from 100, 80, 60, 40 and 20 mL/cm H2O, the average resistance using the Limb-O circuit was 4.73, 4.92, 5.45, 6.27, 8.52 cm H2O/L/sec respectively, and using the heated-wire circuit was 1.77, 2.09, 2.48, 3.03, 4.3 cm H2O/L/sec respectively. This trend in expiratory resistance was similar at each PEEP setting.

Conclusion: Based on these findings, there is an increase in resistance across the expiratory limb of the Limb-O circuit as compared to a heated-wire circuit when ventilating an electronic lung simulator. Additional studies are needed to determine whether or not this is clinically significant on patients. This study was performed without additional heat or humidification; results may vary when using heated, humidified circuits.


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