Abstract 326: Prehospital Use of Nasal Cannula End-Tidal CO 2 Monitoring in Non-Intubated Major Traumatic Brain Injury Patients

Abstract

Objective: Little is known about End-Tidal CO 2 monitoring using nasal cannula sensors (NC-CO 2 ) in non-intubated patients. Objective: To describe the patterns of NC-CO 2 seen during the EMS care of spontaneously breathing major Traumatic Brain Injury (TBI) patients. Methods: Continuous NC-CO 2 data (Philips MRx™ monitors) were evaluated from non-intubated, major (moderate, severe, critical) TBI cases (4/13-5/17) in the EPIC TBI Study (NIH 1R01NS071049). Descriptive statistics were used to evaluate case and NC-CO 2 attributes. Results: Included were 92 cases [median age = 50 (range 10-91; 66% male)]. Median respiratory rate (RR) was >15/min in 87% of cases and >20/min in 53%. The highest median RR was 39. Sixteen cases (17%) had a median NC-CO 2 <20 mmHg, 37% (34) were 20-29, 18% (17) were 30-34, 25% (23) were 35-45. Two cases (2%) were 45-50, which has not been noted in this population previously. No case had a median NC-CO 2 >50. Several common NC-CO 2 patterns emerged: 1) while the final level varied among patients, the vast majority of cases (79, 86%) attained a stable “plateau” with relatively small variation after that point; 2) ETCO 2 often “ramped up” from <10mmHg to the plateau during the initial few seconds of monitoring (36; 39%); 3) many patients (40; 43%) had near-normal (30-34 mmHg) or even normal (35-45) ETCO 2 plateaus. In 78% of the cases with normal CO 2 plateaus (35-45mmHg), these levels were maintained despite high RR and/or dramatic variations in RR. Conclusions: This initial work identifies that NC-CO 2 monitoring may provide useful information in non-intubated EMS patients. After initial “ramp up,” the vast majority achieved stable readings despite dramatic RR variations. Most patients (53%) were spontaneously hyperventilating at rates more than twice “normal.” Despite this, almost half of them (43%) had ETCO 2 plateaus that were normal/near normal throughout their course. It is unclear whether the “very low” readings (<30mmHg) represent true physiological hypocapnia or simply “washout” due to the sensors being in an open ventilatory space (the naris) with continuous ambient O 2 flow. Future studies comparing NC-CO 2 to measured arterial pCO 2 are needed to identify the correlation and accuracy of NC-CO 2 as a tool for evaluating ventilatory physiology.