The Science Journal of the American Association for Respiratory Care

2010 OPEN FORUM Abstracts


Joseph Orr1, Lara Brewer1, Michael Jaffe2; 1Anesthesiology, University of Utah, Salt Lake City, UT; 2Philips-Respironics, Wallingford, CT

Introduction: Respiration rate (RR) is often used as a simplistic indicator of ventilation adequacy when the patient is exhibiting spontaneous ventilation effort. The weakness of using RR as the indicator is that the tidal volume may differ greatly from one breath to the next. Currently, all breaths are counted in the RR. Depending on the clinical environment, the level of respiratory effort that should be counted as a breath can differ greatly. For example, when the goal of RR monitoring is to assess adequacy of gas exchange, it may be more physiologically relevant to only count breaths that are sufficiently large to clear the anatomic and apparatus dead volume. Breaths that are too small to clear the serial dead space do not facilitate gas exchange in the alveoli and should therefore not be counted as contributing to CO2 clearance and oxygenation. On the other hand, if the goal of RR monitoring is to assess respiratory effort or readiness for extubation, inclusion of shallow breaths in the reported RR may be more justified. The goal of this study was to investigate how frequently patients exhibit ventilation with very small tidal volume. Methods: We used a volumetric capnometry monitor (NICO2, Philips-Respironics, Wallingford, CT) to record the FowlerÂ’s airway dead space, apparatus dead space and tidal volumes for each breath in 134 patients during various respiratory monitoring conditions (adult intubated OR, adult intubated ICU, adult non-intubated and pediatric intubated OR). Using this data set we evaluated the fraction of breaths for which the tidal volume was too small to clear the serial dead volume (airway + apparatus) of the patient. Results: The table below shows the percent of breaths for which the tidal volume is smaller than serial dead volume in each of the patient types evaluated as well as the number of patients and breaths that were analyzed for each patient type. A total of 340,251 breaths from 134 patients were evaluated. The rate of breaths with insufficient volume was highest (17.3%) in spontaneously breathing, non-intubated patients during sedation. Breaths were least likely to be of insufficient volume in anesthetized, intubated adult and pediatric patients at 0.6% and 0.44% respectively. Conclusions: Monitoring algorithms that report breath rate or calculated indices based on a simple breath rate while not indicating the presence of very small breaths may fail to indicate the possibility of hypoventilation. Sponsored Research - Philips Frequency of Inadequate Breaths