The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

LABORATORY EVALUATION OF THE VENT F2 BREATHING CIRCUIT

Paul Austin* CRNA MS (LtCol USAF NC), Robert S. Campbell RRT, FAARC, Jay A. Johannigman MD, Sandra L. Miller MD, Fred A. Luchette MD, Kenneth Davis Jr. MD, Richard D. Branson BA, RRT. Division of Trauma/Critical Care and College of Nursing*, University of Cincinnati College of Medicine

Introduction: The Universal F2 (King Systems) is a coaxial breathing circuit designed for use during anesthesia. A recent modification of this circuit (Vent F2) allows its use with an ICU ventilator. We evaluated a 60" version of the Vent F2 in the laboratory on a spontaneous breathing lung model.

Methods:
A two-chamber test lung (TTL) was modified to simulate spontaneous breathing with the addition of a lift bar. A Drager E4 was used to "drive" the lung model with two drive conditions: 300 ml VT @ 30 L/min inspiratory flow and 500 ml VT @ 60 L/min inspiratory flow using a constant inspiratory flow pattern. Test lung was set to a compliance of 50 ml/cmH2O and resistance of 5 cmH2O/L/sec. A T-Bird ventilator was used to ventilate the "patient lung" via the Vent F2 circuit in the CPAP mode with the following combinations of PEEP/Pressure Support: 0/0, 0/10, 5/0, and 5/10. Measurements included peak inspiratory and expiratory flow rate, imposed work of breathing (WOBi), VT, and peak negative pressure (PNP) during inspiration. Measurements were repeated with a 60" two-limb breathing circuit (Hudson) for comparison. Resistance (inspiratory, expiratory, and total) of both circuits was measured as pressure drop across the appropriate portion of the circuit at a constant flow of 1 L/sec. Compliance of each circuit was measured by injecting known volumes from a calibrated syringe into each circuit and measuring the internal pressure. Pressure was measured with a calibration analyzer (RT-200).

Results:
There were no differences between the two breathing circuits with respect to VT delivery, peak inspiratory flow rate, WOBi, and PNP at any test condition. Peak expiratory flow rate with the Vent F2 was generally 20% lower than the conventional circuit at all test conditions. Table 1 reveals the compliance and resistance characteristics of each breathing circuit.

Table 1. Resistance (cmH2O/L/sec) Compliance
Inspiratory Expiratory Total (cc/cmH2O)
Vent F2 3.1 3.2 6.0 1.33
Conventional 0.53 0.28 0.94 1.89

Conclusion: The Vent F2 coaxial breathing circuit is acceptable for use with spontaneous breathing patients with ICU ventilators in the post-operative period. Future studies should assess the potential financial savings, use of the Vent F2 with various humidification techniques, and use of the Vent F2 in patients with obstructive lung disease.

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