Nasal Sensor Capnographic Differences in Major Traumatic Brain Injury Patients Receiving Non-rebreather Mask Versus Nasal Cannula Oxygen Delivery

Background: The advent of highly sensitive End-Tidal CO2 (ETCO2) sensors allows effective monitoring of intubated patients in EMS. Previous work has explored the use of ETCO2 monitoring in non-intubated patients with sensors placed in the nares. However, little is known about the effect of passive O2 delivery [nasal cannula (NC) or high-flow, non-rebreather mask (NRB)] on ETCO2 measurement. Objective: To compare ETCO2 measurements in non-intubated Traumatic Brain Injury (TBI) patients receiving O2 via NC vs. NRB in the field. Methods: A subset of cases from the EPIC EMS TBI Study (NIH-1R01NS071049) were evaluated (4/13-4/18). Non-intubated cases from 5 EMS agencies providing monitor data, including continuous ETCO2. Start and end segments were excluded to remove artifact from initiation (“ramp-up”) or termination of monitoring. Statistics: Wilcoxon rank-sum test, two-sample t-test, and Chi-squared test were used as appropriate. Linear regression compared continuous variables in adjusted analyses (α = 0.05). Results: Included were 151 cases [median age: 52 (range: 9-91; 66% male)]. Of those, 62 (41%) received NCO2 and 89 (59%) via NRB. Patient-level mean ETCO2 was slightly lower in the NC group (mean = 26.9 mmHg; SD 6.7) compared to NRB (mean 30.2; SD 8.1; p=0.007). Differences in the mean were: Unadjusted: 3.3 (95% CI 0.9-5.7); Adjusted 2.7 (0.2-5.2). There were no significant differences in means of the patient-level lowest or highest recorded values. Conclusion: While there was a statistically lower ETCO2 in the NC versus NRB-oxygenated patients, it was around 3 mmHg and, thus, not clinically significant. This is surprising since: 1) the O2 flow rates and 2) the open-air (NC) versus mask (NRB) delivery methods are so dramatically different. Future study is needed to identify the clinical implications of using noninvasive ETCO2 measurement as a tool for monitoring ventilatory status and changes in non-intubated TBI (and other) patients in emergency settings.