The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts


Richard Branson, RRT, Robert S. Campbell, RRT, Kenneth Davis Jr, MD. Department of Surgery, University of Cincinnati Medical Center, Cincinnati, Ohio

Introduction: Artificial noses (AN) are passive humidification devices used to condition inspired gases during mechanical ventilation. We evaluated the moisture output (MO), resistance (Raw), and deadspace (DS) of four AN's according to the ISO standard (ISO 9360:1992). Methods: A patient model consisting of a cascade humidifier, temperature controller, 2 test lungs and a series of tubing and one way valves to separate inspiratory and expiratory flows was constructed. This model was ventilated using compressed air (absolute humidity < 0.7 mg/L) at: 1) V_{T} = 500 mL and f = 20 b/min; 2) V_{T} = 1000 mL and f = 10 b/min; and 3) V_{T} = 1000 mL and f = 20 b/min. During ventilation gas exiting the patient model was controlled to maintain a temperature of 34±1°C. The ventilator used a square flow waveform and I:E of 1:2. The model was weighed and then ventilated for 3 hrs and weighed again to determine water loss (mg/L). Three of each AN were tested for three hours at each ventilation setting and the water loss determined (9 devices each were tested). Moisture output was determined by the ISO equation moisture output = 37.6 x (1- water loss with AN/mean moisture loss without AN). Resistance was determined by monitoring pressure drop across each device using a RT-200 calibration analyzer (Timeter) at a flow of 1 L/s. Results at V_{T} = 1000 mL and f = 10 b/min are shown. Moisture output = mg H_{2}O/L, resistance = cm H_{2}O/L/s and deadspace = mL:

Device Moisture Output Resistance Deadspace

Gibeck Compact 30.3 (1.1) 1.9 (0.1) 41 (2)

Pall BB100 25.1 (1.4) 2.1 (0.1) 90 (2)

King 1000 26.1 (1.0) 2.0 (0.1) 29 (1)

Nellcor PB HME 28.9 (1.6) 1.6 (0.2) 89 (3)

Conclusions: The AARC Consensus Conference on Mechanical Ventilators recommends a minimum absolute humidity of 25 mg H_{2}O/L. The devices tested demonstrate the ability to reach this value. Our results demonstrate that hygroscopic devices are able to deliver more moisture despite a smaller deadspace. This is important when these devices are used with spontaneously breathing patients. None of the devices exceeded the maximum resistance of 5 cm H_{2}O/L/s established by ISO. Practitioners should be aware of the performance of AN's prior to use.


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