The Science Journal of the American Association for Respiratory Care

2010 OPEN FORUM Abstracts


Mark S. Siobal, Laura Martin; Anesthesia, SFGH/UCSF, San Francisco, CA

Background: CO2 rebreathing (RCO2) during NIV is influenced by the mechanical dead space added by the mask and the exhalation valve type. Use of a single limb circuit that lacks a true exhalation valve may cause RCO2 because a portion of the exhaled volume moves down the circuit limb during exhalation. If flow through the exhalation port and expiratory time are less than required to flush exhaled CO2 from the circuit, RCO2 occurs. RCO2 can also be affected by respiratory rate (RR). We tested the effects of RR on RCO2 using two single limb NIV devices. Method: A Michigan Instruments Test Lung with the two chambers locked together was powered on one side (muscle chamber) by a Drager XL ventilator. 100% CO2 was bled into the other side of the test lung (lung chamber) to simulate VCO2. End tidal CO2 (ETCO2) at the lung chamber was measured by the CO2 sensor from the XL ventilator. The muscle chamber was powered at Vt of 600 mL, RR of 20, 25, 30, and 35, I:E ratio of 1:1, and inspiratory flow rate of 100 L/min. CO2 bleed-in to the lung chamber was adjusted until an ETCO2 of 35-40 mm Hg was achieved at each setting. The Drager Carina using a single leak valve (DC1V) and two leak valves in series (DC2V) and a Respironics Vision using two exhalation port types, Plateau Exhalation Valve (VPEV) and Exhalation Port Adapter (VEPA) were tested. Following stabilization at each setting, the test device set to deliver a pressure support PIP of 15 and PEEP of 5 was attached to the lung chamber with a 12 inch section of aerosol tubing placed between the circuit and lung chamber to simulate the mechanical dead space volume of a face mask. The maximum change in ETCO2 from baseline at the lung chamber at each setting combination using each device was recorded. Results: The mean % increase ± STDV and range of ETCO2 changes at all settings was 3 ± 7%, -6% to 11% for the DC2V, 19 ± 10%, 8% to 31% for the VPEV, 26 ± 23%, 0% to 54% for the DC1V, and 64 ± 24%, 34% to 91% for the VEPA. Conclusion: RCO2 and an increase in ETCO2 occurred with all devices tested. RCO2 was greatest using the VEPA and lowest using the DC2V. The impact of RCO2 during the application and study of NIV can be device related and needs to be recognized. Sponsored Research - Received product support for this research project from Drager Medical