Abstract 156: Capnographic Differences in Out-of-hospital Overdose-related, Respiratory, and Cardiac Arrests

Abstract

Background: Little is known about the ventilatory aspects of overdose-related OHCA (OD-OHCA). We compared maximum ETCO2 (mETCO2; each patient’s highest CO2 level) and mean for each recorded minute of CPR in OD-OHCA to that of respiratory (R-OHCA) and cardiac (C-OHCA) arrests. Methods: Continuous CO2 data (Zoll E/X series monitors) were obtained from 3 Arizona EMS agencies. Cases had at least 3 min of recorded CO2 during CPR. Arrests were classified as OD-OHCA by EMS and/or hospital documentation. Any drug OD was included (e.g., opioids, mixed). C-OHCA and R-OHCA cases were randomly chosen for comparison. The groups were compared using Fisher’s exact test or Chi-squared for categorical and Kruskal-Wallis for continuous variables. Results: Included were 263 subjects (37 OD-OHCA, 157 C-OHCA and 69 R-OHCA; median age 61, 64% male, 1/10-12/18) with 10,271 min of data [median resuscitation interval 37 min (IQR 29, 47)]. Mean ETCO2 (SD): OD-OHCA [41 mmHg (24)]; R-OHCA [40 (23)], C-OHCA [30 (13); p<0.01]. Median mETCO2: OD-OHCA [57 mmHg (95CI: 50, 77)]; R-OHCA [61 (50, 73)], C-OHCA [48 (44, 50); p<0.001; Fig 1]. While mean ETCO2 and mETCO2 were similar for OD-OHCA and R-OHCA, they were both significantly higher than C-OHCA (p<0.01 for all comparisons). ETCO2 waveforms in OD-OHCA resembled the very high, full waveforms typical of R-OHCA while those in C-OHCA tended to be low and blunted. Conclusions: We believe this is the first report of continuous capnography during resuscitation of OD-OHCA. The mean ETCO2 and median of mETCO2 of OD-OHCA and R-OHCA imply similar physiology (hypoventilation and hypercapnia leading to arrest). Both etiologies had much higher ETCO2 values compared to C-OHCA, where low blood flow delivers minimal CO2 to the lungs and yields low, and morphologically different, waveforms. Future studies assessing OD arrest physiology and various approaches to resuscitation and pharmacological reversal are needed.