The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts


John W. Newhart, Richard M. Ford, Elsie Collado-Koman; Respiratory Care, UC San Diego Med Ctr, San Diego, CA John Newhart, Elsie Collado Koman, Richard M Ford, UC San Diego Medical Center San Diego CA.

Background: At our institution Bi-level or APRV are used as a lung protective strategy. Staff has noticed that when incorporating very short expiratory phases, the ETCO2 readings in many cases would decrease. While some changes may be attributed to the impact of respiratory physiology, we sought to examine breath mechanics as reasons for the decrease. We devised a bench top study to examine the impact of decreasing e-time on ETCO2 readings, while CO2 production was held constant. Methods: Test were performed using 4 different ETCO2 monitors: Phillips NICO, Oridion Microcap, Phillips Intelivue with an Oridion module, and a GE Datex S5 with gas module. We assembled a two chambered TTL with lift bar. One chamber was ventilated (master chamber) with 0% CO2 and the other (slave chamber) was being moved by the lift bar. CO2 production and ETCO2 was modeled by filling the slave chamber with a constant concentration of CO2 from a mechanical blender. The result being the different sampling lines and sensors were exposed to zero percent CO2 on inspiration and a fixed concentration of CO2 on expiration thus simulating a patient being mechanically ventilated. A Puritan Bennet 840 ventilator was set to drive the master chamber using Bi-level at pressure at a P-Low of 0 and a P-High of 15, at a RR of 14. The Expiratory Time or Time-Low was set at each of the following 2.16, 1, 0.5, and 0.25 seconds. Measures of ETCO2 were recorded on each setting. Results: The capnograms displayed on each device resembled that of typical respired CO2 pattern and ETCO2 readings displayed. As indicated in the table, all four monitors displayed a decrease in ETCO2 as Time Low was sequentially decreased, ranging from an average of 36 mmHg to that of 13 mmHg at the lowest expiratory time. Conclusion: In our bench model, very short expiratory (T low) times corresponded to decreased displayed ETCO2 readings in all devices. It does appear that shortened expiratory times in using Bi-Level breath patterns may either limit alveolar emptying or that there is some other property related to device sampling/response that limits CO2 readings. Further evaluation is necessary; however clinicians should be aware of this issue when evaluating ETCO2. Sponsored Research - None ETCO2